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THESIS

AN INVESTIGATION OF THE WATERS OF
THE EAST GREENLAND CURRENT

by

Mark D. Tunnicliffe

September 1985

Thesis Advisor

Robert H. Bourke

Approved for Public Release; Distribution Unlimited

Prepared for:

Director, Arctic Submarine Laboratory

Naval Ocean Systems Center,

San Diego, Ca . , 92152

T227863

NAVAL POSTGRADUATE SCHOOL
Monterey, California

Rear Admiral R. H. Schumaker D. A. Schrady

Superintendent Provost

This thesis prepared in conjunction with research sponsored by Arctic
Submarine Laboratory, Naval Ocean Systems Center, San Diego, California under
N66001-84-WR-00376. Reproduction of all or part of this report is authorized.

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1. REPORT NUMBER

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4. TITLE (and Subtitle)

AN INVESTIGATION OF THE WATERS OF THE
EAST GREENLAND CURRENT

S. TYPE OF REPORT & PERlOO COVEREO
FINAL

1 Aug. 1984 - 30 Sept. 1985

6. PERFORMING ORG. REPORT NUMBER

7. autmorc*;

Mark D. Tunnicliffe

in conjunction with R.H. Bourke and

R.G. Paquette

6 CONTRACT OR GRANT NUMBER(i)

N66001-84-WR-00 376

». PERFORMING ORGANIZATION NAME AND ADORESS

Naval Postgraduate School,
Monterey, California, 93943

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Arctic Submarine Laboratory,

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San Diego, California, 92152

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September 1985

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136

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18 SUPPLEMENTARY NOTES

'9 KEY WORDS 'Continue or. reverse eide It neceeeary end Identity by block number)

East Greenland Current MIZEX

Icebreaker East Greenland Polar Front
N3RTHWIND Marginal Ice Zone
Greenland Sea Continental Shelf

20 ABSTRACT 'Continue on reveree tide It neceeeary and Identity by block numbar)

A dense network of conductivity-temperature-depth (CTD) measurements made
over the eastern Greenland continental shelf and slope between 81 N and 75 N
privided new detail on the water properties and circulation on the shelf and
at the adjacent East Greenland Polar Front (EGPF) . Tne EGPF approaches the
shelf break rapidly between 80°N and 78°N remaining 20 to 30 km east of it
thereafter at least until 75°N. A filament of Atlantic Water (AW) was found
close to the eastern side of the front which became generally cooler with

DO ,:°nRM73 1473

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decreasing latitude, suggesting that the majority of the contribution of
the West Spitzbergen Current to the southward flowing Return Atlantic
Current occurs north of 78°N. The portion of the shelf investigated is cut
by several troughs generally oriented east-west; two of which are joined
by a north-south depression west of Belgica Bank. Dynamic topography,
water properties and ice movement suggest an anti-cyclonic surface circula-
tion over this system of troughs and banks with AIW advecting up the troughs
from the east.

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An Investigation of the Waters of the
East Greenland Current

by

Mark D. Tunnicliffe
LCDR, Canadian Forces
B.Sc, McMaster University, 1972

Submitted in partial fulfillment of the
requirements for the degree of

MASTER OF SCIENCE IN OCEANOGRAPHY
from the

NAVAL POSTGRADUATE SCHOOL
September 1985

ABSTRACT

A dense network of conductivity- temperature-depth (CTD)
measurements made over the eastern Greenland continental
shelf and slope between 81°N and 75°N provided new detail on
the water properties and circulation on the shelf and at the
adjacent East Greenland Polar Front (EGPF). The EGPF
approaches the shelf break rapidly between 80°N and 78°N
remaining 20 to 30 km east of it thereafter at least until
75°N. A filament of Atlantic Water (AW) was found close to
the eastern side of the front which became generally cooler
with decreasing latitude, suggesting that the majority of
the contribution of the West Spitzbergen Current to the
southward flowing Return Atlantic Current occurs north of
78°N. The portion of the shelf investigated is cut by
several troughs generally oriented east-west; two of which
are joined by a north-south depression west of Belgica Bank.
Dynamic topography, water properties and ice movement
suggest an anti- cyclonic surface circulation over this
system of troughs and banks with AIW advecting up the
troughs from the east.

TABLE OF CONTENTS

I. INTRODUCTION 12

A. PURPOSE 12

B. BACKGROUND 13

1. General 13

2. General Circulation 14

3. Water Masses 15

4. Current Velocities and Transports .... 17

5. The East Greenland Polar Front 18

6. Finestructure and Mesoscale Features

at the EGPF 18

C. APPROACH 19

II. METHODS AND MEASUREMENTS 21

A. MISSION SUMMARY 21

B. INSTRUMENTATION 21

1. CTD 21

2. Data Recording and Display 22

3. Navigation 24

C. DATA PROCESSING AND COMPUTATIONS 24

1. Data Processing 24

2. Resolution 25

3. Computations 25

D. BATHYMETRY 27

E. ICE COVERAGE 28

III. OBSERVATIONS AND RESULTS 33

A. INTRODUCTION 3 3

B. THE EAST GREENLAND POLAR FRONT 33

1. Water Characteristics 37

2. Proximity to the Shelf Break 41

3. The Return Atlantic Current 42

4. Displacement of the Surficial Front ... 46

5. Finestructure 47

6. Mesoscale Features 49

7. Frontal Variability 50

C. THE CONTINENTAL SHELF 64

1. Introduction 64

2 . Regional Hydrography 64

3. Shelf Water Masses 81

D. CIRCULATION AND TRANSPORT 90

1. Introduction 90

2. Dynamic Topography 93

3. Vertical Sections of Baroclinic

Velocity 99

4. Circulation 112

IV. CONCLUSIONS 118

APPENDIX A: MOLLOY DEEP 120

LIST OF REFERENCES 126

INITIAL DISTRIBUTION LIST 129

LIST OF TABLES

I Freezing Stress in the Northern Greenland Sea . . 29

II A Summary of Frontal Characteristics for
Transects Across the EGPF 36

III Frontal Geostrophic Current Sections 102

LIST OF FIGURES

1.1 General circulation and bathymetry of the

Greenland Sea 15

2.1 A map depicting the NORTHWIND 1984 cruise track

and CTD locations 23

2.2 Bathymetry of the northeast continental shelf

of Greenland 28

2.3 Observed ice conditions 31

2.4 A NOAA 7 visual image of the ice margin on 27

Aug 1984 32

3.1 Location of transects across the EGPF 34

3.2 A T/S plot of stations at the EGPF 38

3.3 A T/S plot of stations within the RAC 44

3.4 Transect 1 51

3.5 Transect 2 52

3.6 Transect 3 53

3.7 Transect 4 54

3.8 Transect 5 55

3.9 Transect 6 56

3.10 Transect 7 57

3.11 Transect 8 58

3.12 Transect 9a 59

3.13 Transect 10 60

3.14 Transect 11 61

3.15 Transect 12 62

3.16 Transect 13 63

3.17 Location of transects made on the shelf 65

3.18 Transect 9 70

3.19 Transect 14 71

3.20 Transect 15 72

3.21 Transect 16 73

3.22 Transect 17 74

3.23 Transect 18 75

3.24 Transect 19 76

3.25 Transect 20 77

3.26 Transect 21 78

3.27 Transect 22 79

3.28 Transect 23 80

3.29 A TS plot of typical shelf stations 82

3.30 Thickness of the -1.7°C layer 84

3.31 Surface temperature distribution 87

3.32 Surface temperature distribution - Deviation

from freezing 88

3.33 Surface salinity distribution 89

3.34 Bottom temperatures - deviation from the

freezing point 91

3.35 Distribution of bottom salinities 92

3.36 Dynamic height: surface referenced to 150 dbars . . 94

3.37 Dynamic height: surface referenced to 200 dbars . . 95

3.38 Dynamic height: surface referenced to 500 dbars . . 96

3.39 Dynamic height: 150 dbars referenced to 500

dbars 97

3.40 Location of vertical baroclinic current

sections 100

3.41 Sections 1-3 105

3.42 Sections 4-6 106

3.43 Sections 7-9 107

3.44 Sections 10-12 108

3.45 Sections 13a and 13b 109

3.46 Sections 14-16 110

3.47 Sections 17-19 112

3.48 Sections 20 and 21 113

3.49 General circulation over the shelf and at the
adjacent EGPF 116

3.50 Sea ice drift 1976 After Vinje (1977) 117

A.l Bathymetric and ice structure at Molloy Deep . . 123

A. 2 Transect across Molloy Deep 124

A. 3 Baroclinic velocity field near Molloy Deep . . . 125

10

ACKNOWLEDGEMENTS

Funding for the work described in this thesis was
provided by the Arctic Submarine Laboratory, Naval Ocean
Systems Center, San Diego, California under Work Order
N-66001-84-WR00376.

I wish to thank Dr. R.H. Bourke and Dr. R.G. Paquette
for their advice and guidance during the analysis of the
results and the preparation of this thesis. The assistance
from Dr. J.L. Newton is also gratefully acknowledged. The
success of the cruise and the large quantity of data
acquired is to a great extent a reflection of the enthusiasm
of the crew of the USCGC NORTHWIND, and in particular to the
personal interest of her Commanding Officer, Captain W.
Caster.

Finally, I wish to acknowledge the support of my wife,
Nancy, whom I deserted with two small children to cruise
amid the ice and who defended me from interruption while
this thesis was being written.

11

I. INTRODUCTION

A. PURPOSE

The cruise of the USCGC NORTHWIND to the north-east
coast of Greenland during the summer of 1984 provided, by
means of a relatively dense network of conductivity-
temperature-depth recorder (CTD) stations, a wealth of
information on the circulation, water masses, and hydro-
graphic structure of the major oceanographic feature in this
region, the East Greenland Current. This cruise, the third
in a series of hydrographic surveys designed to investigate
the East Greenland Current (EGC) north of 75°N, provided
information on the characteristics of the water overlying
the continental shelf and the area immediately east of the
shelf break between 75°45'N and 81°20'N. This thesis pres-
ents an analysis of the information collected during that
cruise .

The major purpose of the cruise was to investigate the
water masses and circulation over the troughs and banks of
the shelf. An additional objective was to make a series of
crossings of the boundary between the EGC and the warmer
Greenland Sea water to the east, and to determine what, if
any, interactions occurred between this deeper region and
the shelf waters. This boundary zone is characterized by a
sharp temperature and salinity gradient and will be referred
to as the East Greenland Polar Front (EGPF) after Wadhams et
al. (1979, p. 1325).

Because of the normally heavy ice concentrations
encountered on the shelf, even in summer, relatively little
information has been obtained concerning the oceanographic
features of this region. However, during the NORTHWIND 1984

12

cruise, ice conditions over the shelf and in the marginal
ice zone (MIZ) were unusually light, allowing the cruise
objectives to be largely met. Only a small portion of the
area of interest proved to be inaccessible.

The objective of the analysis of the CTD data presented
in this thesis will be to:

• characterize the north-south development of the EGPF
using temperature-salinity transects and contours of the
vertical baroclinic geostrophic current velocity field,

• describe the water masses found over the shelf region
and observe how bathymetry and other factors affect the
distribution of water characteristics, and

• make some inferences about the circulation over the
shelf and at the front by examining the distribution of
water characteristics and the dynamic topography.

B . BACKGROUND

1 . General

The EGC is the major outlet for Arctic Ocean surface
water into the Atlantic Ocean. The presence of this
current, which carries significant quantities of ice through
Fram Strait between Greenland and Svalbard and through the
Denmark Strait to Cap Farvel, has been known for some time.
Aagaard and Coachman (1968a) provide a comprehensive review
of studies of the EGC up to and including the 1964 and 1965
EDISTO expeditions. Some direct current measurements along
much of the north-south extent of the EGC were made during
the drift of the ice island ARLIS II during the winter of
1964/65, and another three were made over Belgica Bank by
EDISTO in the summer of 1965. An under-ice investigation of
the EGC was conducted by HMS/M SOVEREIGN in the fall of

13

1976 using a recording velocimeter (Wadhams et al.,1979).
Beginning with the summer 1979 WESTWIND expedition, a series
of Arctic Submarine Laboratory sponsored cruises commenced
high resolution CTD surveys of the northern portion of the
EGC. The WESTWIND 1979 cruise (Newton and Piper, 1981;
Newton, in preparation) penetrated the shelf at 77°N and
80°N, while the autumn 1981 NORTHWIND cruise (Perdue , 1981 ;
Paquette et al.,1985) executed a series of transects across
the EGPF east of the continental slope between 76°N and
78°N.

2 . General Circulation

The general bathymetry and circulation in the
Greenland Sea is presented in Fig. 1.1. This figure (taken
from Paquette et al.,1985) indicates the estimated circula-
tion pattern based on various sources up to and including
the results of the NORTHWIND 1981 cruise. The surface circu-
lation in the Greenland Sea is dominated by a large cyclonic
gyre bounded to the south by the Jan Mayen Current and to
the east by the Norwegian and West Spitzbergen Currents. In
the northern portion of the Greenland Sea, the West
Spitzbergen Current (WSC) splits, with a portion turning
westward and subsequently submerging and turning southward.
This branch of relatively warm water, called the Return
Atlantic Current (RAC), together with the EGC, accounts for
the flow of water in the western portion of the Greenland
Sea. The RAC consists of relatively warm and saline water
compared to the cold fresher surface waters of the EGC, and
the conjunction of the two provides the sharp east-west
gradient of water properties which comprise the EGPF.
Paquette et al. (1985) characterize the RAC as being less
than 100 km in breadth and submerged under the EGPF at
depths of 50 to 300 m.

14

Figure 1 . 1

A map showing the general bathymetry and
circulation in the Greenland Sea (from Paquette
et al., 1985, p. 4867). Note that Belgica "Dyb*
in this figure is referred to as Belgica Trough
in this work.

15

3 . Water Masses

Aagaard and Coachman (1968a) have identified three
major water types found in the EGC. Their definitions,
which have been accepted by much of the succeeding
literature, are adopted here.

The Polar Water (PW) fraction extends from the
surface to 150 to 200 m and is colder than 0°C. This layer
increases rapidly in salinity with increasing depth. Surface
salinities often are less than 30.0 and increase to about
34.5 at the bottom of the layer. The PW fraction of the EGC
is generated in the Arctic Ocean but its characteristics are
modified somewhat by local processes such as ice melt and
freezing as well as insolation and mixing.

Atlantic Intermediate Water (AIW) is found both
under the PW and, at the EGPF , to the east of it. AIW
consists of water warmer than 0°C with salinities increasing
from the PW maximum to a value between 34.88 and 35.00 at
about 400 m, remaining relatively constant thereafter. The
Swift and Aagaard (1981, p. 1111) lower limits for Atlantic
Water (AW), temperature 3°C, salinity 34.9, set the upper
limits for AIW. Aagaard and Coachman (1968b, p. 282) state
that the AIW fraction of the EGC has its origin in the WSC,
deriving from a westward movement of warm Atlantic Water
(AW) beginning north of 75°N and continuing over a range of
latitudes to at least 80°N. Not all of the upper layer of
the AIW can be formed by simple mixing of PW with the AW
found in the WSC. Paquette et al. (1985, p. 4878) demon-
strate that the AIW overlain by PW contains a fraction which
is too cold to have been formed by mixing and suggest that
double diffusion, local freezing, or advection from the
north may be responsible.

Underlying the AIW at depths generally greater than
800 m is the Greenland Sea Deep Water (GSDW) . It is

16

comprised of water colder than 0°C and limited by a narrow
salinity range of 34.87 to 34.95.

4 . Current Velocities and Transports

The current velocity of the EGC shows considerable
spatial variation and probably large scale temporal varia-
tion as well. Aagaard and Coachman (1968a) summarized the
current meter measurements made during the diagonal passage
of the EGC by the ice island ARLIS II in the winter of 1965
as well as those by EDISTO over Belgica Bank in the same
year. They concluded that the surface current velocity
increases to the south from 0.04 m/s southeast of Belgica
Bank to 0.14 m/s at 70°N and decreases in speed over the
continental shelf. They also noted that there appeared to be
no large decrease in velocity with depth, at least to depths
of 340 m in winter, although they conceded that the baro-
clinic contribution to the current flow may be more signifi-
cant in summer. On the basis of these results they computed
a volume transport of 35 Sv , an order of magnitude higher
than previous estimates (e.g. Vowinckel and Orvig (1962),
Mosby (1962)).

Baroclinic estimates of current velocities north of
75°N vary somewhat from year to year, as may be expected,
but in general show highest values over the shelf break in
the region of the EGPF and decrease westward. Maximum values
of 0.23 m/s were reported by Aagaard and Coachman (1968b, p.
280) from the 1965 EDISTO Nansen bottle/reversing thermom-
eter data, and 0.15 to 0.20 m/s by Newton (in preparation)
from the 1979 WESTWIND results. Both of these calculations
were made with respect to a 200 dbar level of assumed no net
motion. Paquette et al. (1985) suggest that the frontal jet
may exhibit much higher velocities. The closer station
spacing across the front made during the NORTHWIND 1981
cruise and the use of a 500 dbar reference indicated speeds
up to 0.96 m/s at 77°25'N just inside the ice edge.

17

5 . The East Greenland Polar Front

The eastern edge of the EGC is characterized by a
strong east-west gradient in temperature and salinity which
marks the East Greenland Polar Front and which forms a
boundary between the PW of the EGC and the AIW and AW of
the central Greenland Sea to the east. At the EGPF , the
isotherms and isohalines characterizing the PW of the EGC
and the underlying AIW turn sharply upward toward the east.
The slope of the front appears to show considerable spatial
and temporal variability. For example, Aagaard and Coachman
(1968b) reported a mean slope of 1 m/km over a range of 120
km derived from a transect taken across the EGPF at 75°N in
1965. Newton and Piper (1981) report a mean slope of
3.3 m/km over 60 km at 78°N in 1979. Perdue (1982) noted
mean slopes of 1.5 m/km to 20 m/km between 78°N and 76°N.
In a subsequent transect conducted eight days later, this
latter value, which was derived from a transect conducted at
the mouth of Belgica Trough, was reduced to 8.5 m/km.

The EGPF is the location of the fastest currents in
the EGC. Paquette et al. (1985, p. 4877) present a section
showing baroclinic north-south components of current
velocity derived from the NORTHWIND 1981 data at 78°N which
shows a narrow, shallow jet (35 km wide, 100 m deep, as
defined by the 0.05 m/s isotach) at the EGPF.

6 . Finestructure and Mesoscale Features at the EGPF

The relatively high vertical-resolution sampling
provided by the CTD measurements made during the WESTWIND
1979, NORTHWIND 1981, and the present cruise has permitted
resolution of finestructure in the EGPF. During NORTHWIND
1981, lenses of alternating cool and warm water with peak-
to-peak temperature excursions of up to 1.0°C were noted in
the AIW between 75 and 300 m by Paquette et al. (1985). They

18

propose that this interleaving of water of different temper-
atures is the result of parcels of AIW or AW east of the
front, at or near the surface, which have undergone cooling
and slight dilution and have descended westward along the
sloping isopycnals of the front.

Another feature of the front is the presence of
meanders and eddies, usually in the AIW just east of the
EGPF. Paquette et al . (1985, p. 4874), compared the EDISTO
1965 and NORTHWIND 1981 cruises and noted a cyclonic eddy
in much the same location in both cases. This eddy, gener-
ally located at about 79°30'N, 001°E is quasi-permanent and
appears to be associated with the 5570 m Molloy Deep.
Further discussion on this phenomenon is provided in
Appendix A.

Newton (in preparation) noted a front configuration
at 79°N during the WESTWIND 1979 cruise which was consistent
with the cyclonic circulation associated with the Molloy
Deep feature together with appeared to be a parcel of PW
detached from the EGC east of the front. He observed that
the density structure of this 30 km feature was consistent
with an anticyclonic eddy with a Rossby radius of
deformation of about 10km.

C. APPROACH

The succeeding chapters present an analysis of the
results of the NORTHWIND 1984 data making comparisons with
previous work. One of the most significant features of this
cruise, compared with previous ones, was the large amount of
high resolution data collected on the continental shelf
between 76°N and 81°N. Since previous bathymetries of part
of this region have been somewhat sparse or inaccurate, a
new plot of the bottom topography with adequate resolution
for the purposes of this work was developed based on depth

19

observations made at each CTD station. Supplemental depth
data obtained from the CTD stations of the WESTWIND 1979 and
NORTHWIND 1981 cruises was incorporated as well. This bath-
ymetry, along with a review of the method and instruments
employed, and a synopsis of the ice conditions encountered
is presented in Chapter 2.

Results of the data analyses are included in Chapter 3.
The water masses, structure and development of the EGPF are
presented using temperature- salinity cross- sect ions across
the front as well as temperature-salinity (T/S) plots of the
water structure at individual stations in the frontal
region. A similar approach is used to examine the hydrog-
raphy of the shelf. Additionally, an analysis of the circu-
lation pattern at the front and on the shelf is presented
using dynamic topography, distribution of water properties
and, in one instance, ice drift.

20

II. METHODS AND MEASUREMENTS

A. MISSION SUMMARY

Between 22 August and 16 September 1985, the USCGC
NORTHWIND conducted an extensive hydrographic survey of the
waters of the East Greenland Current including the shelf
waters of the northeast Greenland coast. In the course of
this cruise, NORTHWIND made a series of crossings of the
continental shelf break between 80°N and 75°30'N, many of
which extended inward close to the Greenland coast.
Detailed transects were conducted over prominent shelf
features such as Ob' and Belgica Banks, Belgica Trough and
Westwind Trough (see Fig. 2.2 for the location of the place
names listed) . The ship approached the coast closely enough
to conduct surveys in Ingolf's Fjord and Dijmphna Sund in
the north, and along the east and south coasts of lie de
France further south. NORTHWIND covered almost 6500 km in
the course of conducting 333 CTD stations. Operations were
augmented and assisted with the use of the ship's Arctic
Survey Boat in shallow water and by the NORTHWIND' s two
helicopters which conducted some 45 sorties in ice recon-
naissance. The cruise track and location of CTD stations are
shown in Fig. 2.1.

B. INSTRUMENTATION
1. CTD

The Neil Brown Instrument Systems (NBIS) Mark III
CTD was the primary instrument used to make the oceano-
graphic observations. A wire cage, supported by a metal
frame, was appended to the base of the instrument to protect

21

the sensors against impact with ice and with the ocean
floor. No significant deterioration of sensor response due
to this adaptation has been observed (see also Paquette et
al. 1985, p. 4876). The CTD was fitted with a calibrated
3200 decibar pressure sensor which provided adequate depth
resolution for the purposes of the cruise and facilitated
making deeper casts off the shelf.

The temperature and conductivity sensors were cali-
brated before and after the cruise. Because of a possible
error in one or the other measurement, a comparison of pre-
and post-cruise conductivity calibrations was inconclusive
for accuracy levels better than 0.5 S (0.005 ohm-lcm-1).
Evidence of long-term stability in both temperature and
conductivity was provided by a comparison of salinity meas-
urements taken at two adjacent stations - one made at the
beginning of the cruise and one towards the end - which
suggested that a difference no greater than 0.001 ppt was
likely to have occurred. This comparison was made at depths
below 600 m where the salinity profile is quite stable.

None of the difficulties noted by Perdue (1982, p.
62) with water freezing in the sensors between casts was
experienced during this cruise since the ambient air temper-
ature was greater than -2°C for much of the time. The CTD
sensors were conditioned prior to each recording by repeated
flushing to 50 m. The lack of any notable or consistent
differences in the near-surface measurements made during the
up and down traverses of the CTD showed that this technique
was adequate.

2 . Data Recording and Display

The data were passed from the CTD via the NBIS deck
unit to a Hewlett-Packard 9835B computer where it was stored
on magnetic tape cassettes. For flexibility in storing data,
and to economize on tape usage, the computer and tapes were

22

5 W

Figure 2.1 A map showing the NORTHWTND 1984 cruise track
and CTD station locations. The location of the
EGPF and the 300 m isobath are also shown.

23

formatted to accept either 3500, 2625, 1750, or 875 binary
data records. This allowed tapes to store data to approxi-
mately 1200, 900, 600, or 300 m, respectively. When it
became clear that the supply of tapes was going to be
limiting, only the data from the down casts were recorded.
However, the 10 kHz modulated audio signal from the CTD for
both up and down casts was recorded on a back-up Sony audio
tape recorder. Additionally, in water of less than 150 m
depth, both up and down casts were recorded in digital
format since both sets of data would then fit on the minimum
length file.

Data for both up and down casts at all stations were
immediately plotted on a Hewlett-Packard 9872A X-Y flat bed
plotter and later, on the back-up H-P 9225B plotter.
Temperature and salinity plots of the up casts were plotted
on the same graph as the down casts (offset by half a scale
unit) to permit comparison.

3 . Navigation

The primary navigation aid was the Magnavox MX 1107
Satellite Navigation System, which provided an average of
two fixes per hour with a mean accuracy of 0.5 km.

C. DATA PROCESSING AND COMPUTATIONS

1 . Data Processing

A number of spikes in the CTD data were noted as
temperature and salinity profiles were generated on the X-Y
plotter. The causes of such spikes are not certain but are
possibly due to a combination of plankton or ice particles
passing through the conductivity cell, power surges, slip-
ring noise, or instrument peculiarities. The spikes were
occasionally serious enough to cause the plotting routine to
fail completely. This problem was solved by modifying the

24

H-P computer program to ignore out-of-range single data
points .

Upon conclusion of the cruise, the data were trans-
ferred to a tape format more suitable for processing by the
NPS IBM 3033 computer. At this point the data were edited to
remove single spurious data points and data mis- sequenced in
terms of depth (caused by the roll of the ship during a
cast). The temperature and conductivity were corrected for
dynamic response errors, thus compensating for the salinity
spikes produced by the mismatch of response time in conduc-
tivity and temperature, empirically found to be 23 and 110
ms , respectively. The resulting despiked salinities were
smoothed with a five point centered running mean.

2 . Resolution

The data sampling rate was set to provide for one
conductivity/ temperature/pressure recording every 36 cm
based on a CTD lowering rate of 1 m/s, providing a vertical
resolution in the data of about three points per meter. To
monitor the lowering/raising rate of the CTD, the H-P
computer was programmed to display the actual depth and the
ideal depth, based on the 1 m/s lowering rate, of the CTD
continuously throughout the cast.

A subset of this data was constructed consisting of
one point every 5 m. This subset was used for various ancil-
lary purposes not requiring the full resolution of the orig-
inal data set such as in the construction of vertical
baroclinic velocity profiles and the calculation of volume
transports .

3 . Computations

Dynamic heights, based on the geostrophic approxima-
tion were calculated with reference primarily to the 500
dbar level. Additional computations were made with reference

25

to the 200 and 150 dbar levels which provided an opportunity
to compare the differences resulting from the selection of
different reference levels as well as providing an appro-
priate basis for comparison with earlier work (for example,
Paquette et al., 1985; Newton, in preparation) in which
different reference levels are used.

Over portions of the shelf where the bottom was
often shallower than the reference level selected for
dynamic height computations, the reference level and the
isosteres from the nearest adjacent deep-water station were
projected horizontally into the sea bottom, following the
technique of Helland-Hansen (1934). As pointed out by Fomin
(1964, p. 153), this method assumes that the velocity of the
gradient current at the bottom is zero and therefore that
the horizontal pressure gradient is zero. Since this latter
assumption is probably not true, the use of this technique
introduces some error into the calculations. As pointed out
by Paquette et al. (1985), the regions of greatest velocity
are over deeper water and are therefore not subject to this
inconsistency. The use of a 150 dbar reference level (Fig.
3.36) avoids much of this difficulty since relatively few
such extrapolations were needed. However, use of this refer-
ence level neglects the information inherent in deeper
waters .

The vertical baroclinic velocity cross- sect ions
developed are also normally referenced to 500 dbar with a
300 dbar reference level used when necessary. Reference
levels are noted with the appropriate figures. The
Helland-Hansen (1934) technique was also applied to these
sections when required.

Volume transports were calculated for baroclinic
current velocities referenced to 500 dbar or 300 dbar as
indicated above. They were obtained from vertical trape-
zoidal integration of the baroclinic velocity curve between
each pair of stations in a section with a 5 m vertical grid.

26

D . BATHYMETRY

In order to relate some of the observed oceanographic
phenomena to the shelf topography (where appropriate), and
since older charts were not sufficiently accurate, a bathy-
metric map of the shelf between 75°N and 82°N was
constructed (Fig. 2.2). Bottom contours were constructed
based upon the water depth at CTD stations occupied during
the WESTWIND 1979 and NORTHWIND 1981 and 1984 cruises to
this region. Required details not available from these data
were obtained from using older charts (Perry et al . , 1980).

The eastern continental shelf of Greenland between 77°N
and 81°N is transversely cut by a number of troughs and
depressions. The most notable of these, Belgica Trough
(which may also be referred to elsewhere as Belgica Dyb or
Belgica Strath), cuts the shelf from the shelf break at 77°N
westward to just north of lie de France at 78°N. The mean
depth of this trough is somewhat greater than 300 m but
deeper depressions, in excess of 500 m at the shoreward end,
were noted during the cruise.

Contiguous to Belgica Trough, and running northward
parallel to the coast, is another deep depression tenta-
tively named Norske Trough after the island nearby. Depths
in excess of 600 m were noted near its southern end but much
of it, particularly the portion closest to the shore, could
not be investigated due to the presence of fast ice covering
much of the area.

Norske Trough is connected at its northern end to
Westwind Trough which extends southeasterly from Ingolf's
Fjord. Westwind Trough is somewhat shallower than Belgica
Trough, the axial depth being about 300 m.

Less well defined and running almost north/south is a
depression east of the shallowest portion of Belgica Bank.
This depression lies between Belgica and Westwind Troughs
and parallels the coastline.

27

20*w

15»W

IO*W

5*W

Figure 2.2

A map showing the bathymetry of the north-east
continental shelf of Greenland. This map was
produced by contouring depths measured at CTD
stations during the 1979 WESTWIND and 1981 and
1984 NORTHWIND cruises.

28

E. ICE COVERAGE

During this cruise NORTHWIND was able to penetrate many
areas on the shelf not accessible on previous cruises
because of the relatively low ice concentrations encoun-
tered. This variation in ice coverage is due ultimately to
variations in seasonal weather. Some indication of the rela-
tive mildness of the 1983/84 winter season can be gained
from the freezing degree days in the general area during the
freezing season. Table I indicates the Celsius freezing
degree days experienced at three meteorological stations:
Damatshaven at 76°48'N on the east Greenland coast,
Barentsberg on Svalbard and Malye Karmakuly on the southern
end of Novaya Zemlya. The data suggest that over a wide
range in the area north of the Greenland and Norwegian Seas
that the winter of 1983/84 was relatively mild.

TABLE I
Freezing Stress in the Northern Greenland Sea

Station/Year

Freezing Degree Days (°C)
1979 1981 1984

Damatshaven 4583 4871 4558

Barentsberg N/A 3268 2234

Malye Karmakuly 3342 2793 1788

Ice coverage is a function of local climatic conditions
(as indicated by the number of freezing and warming degree
days) as well as wind and circulation. It is also, to some
extent a function of the climatic conditions in the regions
from which ice might advect . According to Wadhams (1983,
p. 110), ice in Fram Strait is derived from two sources.

29

The ice within 100 km of the MIZ has advected from north of
the Barents and Kara Seas westward across the north of
Svalbard into the Strait. The ice in the western part of
Fram Strait from 79°N - 84°N has advected across the North
Pole region and is comprised of a greater fraction of multi-
year ice. Therefore presumably, climatic conditions in the
Soviet arctic will also have a significant impact on the ice
coverage in the Greenland Sea MIZ.

The ice conditions encountered by NORTHWIND throughout
the 1984 cruise are indicated in Fig. 2.3. Concentrations
are taken from ice density observations made in the local
area during each CTD cast. It is not a fully accurate indi-
cator of the actual ice conditions in the region not only
because of its non-synoptic nature but also because the ship
occasionally had to skirt some of the densest concentrations
which are therefore not recorded. However, it does best
indicate the local ice conditions at the time of each CTD
cast. A photographic view of the ice conditions as recorded
by the NOAA 7 meteorological satellite (visual band) on 27
August is shown in Fig. 2.4 It is representative of NOAA 7
photographs taken throughout the period of the cruise.

Despite differences in their derivations, both Figs. 2.3
and 2.4 show many similar features, including:

• low ice concentration to the north (80°N) especially
near the coast ,

• a somewhat less well developed marginal ice zone (MIZ)
north of 78°N, and

• the presence of a solid mass of fast ice covering much
of the inshore portion of Norske Trough.

30

2C W

15 W

10 w

Figure 2.3

Distribution of ice coverage. This non-synoptic
representation of the ice coverage, indicated in
tenths, is based on the ice concentration noted
at each CTD station. The ice margin on 27
August as determined from a NOAA 7 photograph on
that date is also indicated for comparison.

31

80°N

75°N

Figure 2.4 A NOAA 7 visual image of the ice margin on 27
August 1984. This photograph, typical of the
tuation in August / September 1984, shows little

ice coverage at
somewhat by /5° N.

80'

N with ice increasing

32

III. OBSERVATIONS AND RESULTS

A. INTRODUCTION

The distribution of water properties over the north-
east Greenland shelf and in the East Greenland Current is
primarily depicted in this chapter using temperature and
salinity transects. The area has been divided into two
regions for consideration: the front, located east of the
shelf break, and the shelf proper and its associated banks
and troughs. Sequences of transects in each region were
produced showing the development of the EGC and its water
properties with respect to bathymetry, latitude, or prox-
imity to the coast, as appropriate.

The circulation of water on the shelf is inferred from
dynamic topographies, the horizontal advection of water
properties as well as by examining the geostrophic baro-
clinic current velocity in vertical cross-section over a
series of sections made at various latitudes. Results from
this analysis could be confirmed in one instance using
satellite photographs indicating ice motion.

B. THE EAST GREENLAND POLAR FRONT

NORTHWIND crossed the shelf break seventeen times
between 80°N and 75°45'N during this cruise, but not all of
these crossings included the East Greenland Polar Front
(EGPF). The locations of thirteen temperature- salinity tran-
sects made in the vicinity of the front is indicated in Fig.
3.1. They are numbered sequentially from north to south,
not necessarily in the order in which they were conducted.
Each of the transects was reasonably synoptic being
completed over time spans of 5 to 25 hours during the 25

33

\b w

10 W

Figure 3.1 A map showing the location of transects made
across the continental shelf break.

34

August - 16 September period. One (Transect 9a) was repeated
three days later (as Transect 10); otherwise transects are
separated by 15 to 30 minutes of latitude and run perpendic-
ular to the direction of the front with the exception of
Transect 12 which crosses the front at about 45°.

Transects 1 to 13 are shown in Figs. 3.4 to 3.16 at the
end of this section. To facilitate the observation of the
north-south evolution of the front as shown in these tran-
sects, a number of characteristics were quantified using
consistent though somewhat arbitrary criteria. The mean
slope of the front is derived by noting the depth of the 0°C
isotherm at the point where it clearly turns upward and the
location of its intersection with the surface (or the upper
boundary of the lower front in the case of a split front)
and then determining the horizontal distance over which
this vertical displacement takes place. While this determi-
nation is clearly somewhat arbitrary, particularly in the
case of the more northerly transects, where the front was
split into upper and lower parts horizontally displaced from
each other, it could be made with reasonable consistency in
most cases. Additionally, since the shape of the front
(again as defined by the behaviour of the 0°C isotherm) is
concave with respect to the PW, instantaneous slopes of the
front at its eastern extremity were considerably greater
than the mean values calculated. The west-east horizontal
thermal gradient was calculated by noting the distance
between the -1.5°C and 2.0°C isotherms at 50 m. Distances
from the shelf were measured from the 400 m isobath to the
point at which the 0°C isotherm intersects 50 m depth. A
summary of the frontal transects and the results of these
calculations is provided in Table II.

A detailed description of the water masses and processes
occurring along the EGPF at the onset of the freezing season
and over a lesser range of latitudes has already been made

35

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36

(Paquette et al., 1985; Perdue, 1982). However, the present
sequence of transects show more clearly the development of a
number of characteristics of the EGPF as the EGC moves
southward. In the following sections, the location of the
front with respect to the shelf, frontal water masses, the
nature of the RAC associated with the EGPF, f inestructure ,
and mesoscale features are discussed.

1. Water Characterist

1CS

A characteristic of the PW close to the EGPF
appears to be a cold (<-1.5°C), relatively saline (about
34.0) fraction which lies close to the bottom of the PW
layer at about 100 m. Another temperature minimum occurs at
a salinity of about 32.3 to 32.8 in many, but not, all
frontal stations. This "double minimum" feature, shown in
Fig. 3.2, persists down the length of the EGPF although the
temperature of the high salinity minimum rises somewhat from
less than -1.7°C (Station 24) at 79°55'N to -1.58°C at
75°35'N (Station 330). There is also a reduction in salinity
from 34.0 to 33.6 of the high salinity temperature minimum
over this latitude range. Cold waters of such high salini-
ties were generally not noted at stations on the shelf
(Station 137 in Fig. 3.2 is a typical example) nor in waters
east of the front (for example, Station 18 in Fig. 3.2).
Another way of observing this feature is to note the behav-
iour of the lower -1.5°C isotherm in the longer frontal
transects (for example Fig. 3.4, 3.6 or 3.7). Over the
shelf, the lower -1.5°C isotherm is almost contiguous with
the 33.0 isohaline but close to the EGPF, this isotherm
changes to the depth at which the 34.0 isohaline is found.
Typically, this happens 20 - 30 km west of the front. In
Transect 1 (Fig. 3.4), where the EGPF lies 120 km east of
the shelf break, this cold saline fraction is spread over an
east-west distance of 75 km. Transect 1 also provides a

37

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38

typical example of the superposition of two cold water
masses of different salinities in the proximity of the
front .

The formation of the cold, saline fraction has led
to some speculation. Kiilerich (1945, p. 28) discussed the
temperature-salinity characteristics of the water in Fram
Strait as observed by the BELGICA 1905 expedition. He postu-
lated that the characteristics of the water were defined by
the mixing of "AW" (2.1°C, 34.97), and "PW" (-1.85°C, 34.00)
which he stated was formed beneath the ice of the polar sea.
Paquette et al. (1985, p. 4878) defined a cold temperature
source for mixing as locally available PW of lowest
salinity (-1.5°C, 30.5). They observed that simple mixing
between this PW and AW (3.5°C, 35.1) would not account for
the "knee" structure they observed in temperature- salinity
diagrams constructed from NORTHWIND 1981 observations made
at 78°N. Their knee at -1.2°C and 34.1 appears similar to
the apex observed at about -1.5°C and 34.0 in Fig. 3.2. They
suggest that the knee is primarily formed by the advection
of AIW from the east under the upper layers of Arctic Ocean
water at which interface some modification, possibly by
double diffusion , occurs.

If one assumes that the cold saline fraction has
advected into the area of the EGC covered by this study, the
question of its origin is raised. Certainly Kiilerich' s
assumption of origin appears somewhat general in light of
more recent data on Arctic Ocean water properties. For
example, in none of the winter 1964/65 stations occupied by
the ice island ARLIS II in the western Arctic Ocean was
water which was more more saline than 34.00, colder than
-1.5°C (Tripp and Kusunoki, 1967). Water approximating
Kiilerich' s "PW" was only noted by Tripp and Kusunoki
further south (72°N - 78°N) off the east Greenland coast
where water with temperatures less than -1.8°C with

39

salinities in the range 33.4 - 34.4 were found in the upper
100 m. This suggests that a source in the western and
central Arctic Ocean is not responsible for the cold saline
fraction.

Aagaard et al. (1981) discussed the formation of
such cold saline water in the Arctic Ocean and suggest two
mechanisms: salinization of cold surface waters by brine
rejection during freezing, and the cooling of AW. The latter
mechanism, they proposed, might occur when AW upwells from a
deep position and is cooled and freshened. The second mecha-
nism, which they explored in some detail, involves the
salinization of shallow shelf water by brine rejection
during winter freezing. In particular, they noted that the
region between Spitzbergen and Franz Joseph Land requires
relatively little ice growth to raise the upper 50 m to a
salinity of 34.5. Cold saline water produced in this loca-
tion or similar regions in the Kara and Barents seas farther
east advecting into the eastern portion of Fram Strait could
account for the cold saline fraction noted in the frontal
station in Fig. 3.2.

The question of the path of such advection is then
raised since the near-surface circulation appears to be
predominantly eastward in these locations. Water formed on
these shelf areas might be postulated to move off the shelf
region and subsequently follow the same path as the first
year ice within the eastern 100 km of the MIZ in Fram Strait
which Wadhams (1983, p. 110) suggests originates north of
the Barents and Kara Seas. Such a speculated flow might be
resolved by the conduct of several zonal transects in the
northern portion of Fram Strait and a comparison of the
water properties in the northeastern portion of the Strait
with those north of the Barents and Kara Seas.

In summer, as the cold saline fraction moves south
in the EGC, some local modifications would occur. Warming by

40

diffusion of heat from underlying AIW could account for the
slight erosion, with decreasing latitude, of the apex in the
T-S properties in Fig. 3.2. The lack of such a sharp knee in
the T-S diagram at 34.0 for stations west of the frontal
region may result from a longer period of erosion in the
slower moving portions of the current over the shelf or
perhaps because the PW over the shelf originates from a
different portion of the Arctic Ocean than that in the
frontal region. This latter suggestion appears to be consis-
tent with the hypothesis of Wadhams (1983, p. 110) that the
ice in this portion of the current was derived from deep
within the Arctic Ocean. It is also supported by the obser-
vations of Tripp and Kusunoki (1967) of temperatures greater
than -1.5°C for water more saline than 34.00 in the central
Arctic .

2 . Proximity to the Shelf Break

Transect 1 (Fig. 3.4) at 79°55'N is the only tran-
sect in which the front is displaced any significant
distance (123 km) from the shelf break (here defined as the
400 m isobath). The front appears to have moved signifi-
cantly closer to the shelf by 79°12'N (Transect 2; Fig. 3.5)
and at Transect 3 (Fig. 3.6), the front is about 20 km from
the shelf. From here southward (at least until 75°55'N),
the front remains within 15 to 40 km of the shelf break.

The front south of 79°N appears to be steered by
bathymetry. Aagaard and Coachman (1968b, p. 269) note that
the front and the shelf break coincide as far south as 73°N,
at which point PW extends eastward again, associated with
the flow of the Jan Mayen Polar Current.

The location of the front north of 78°N varies some-
what from year to year as can be seen by interannual compar-
isons along 79°N. As indicated above, in 1984 the front at
79°N was about 20 km from the shelf break, while Newton and

41

Piper (1981, p. 35) observed it at a distance of 120 km in
1979. Paquette et al . (1985, p. 4874) show the front in
1981 split into an upper and lower portion 45 to 90 km from
the shelf break. The EDISTO 1965 data does not provide
sufficient spatial resolution for satisfactory comparison
but Aagaard and Coachman (1968b, p. 268) show the front at
that time generally departing from the shelf north of
77°30'N and approximately 150 km west of it by 80°N.

Since the position of the EGPF appears to be
controlled by bathymetry for much of its extent north of
73°N, its behaviour above 78°N leads to some speculation. By
about 80°N the position of the front, as indicated by the
location of the ice edge, has changed orientation from
essentially meridianal as it is further south, to to a zonal
configuration near 81°N (see, for example, Fig. 2.4). The
location of the ice edge in summer is largely controlled by
the position of the EGPF although closer to Svalbard the WSC
may be more influential in determining the ice cover in that
area. As will be discussed in the next section, the
majority of the warm water which marks the EGPF turns into
the southward flowing EGC from the east between 79°N to 81°N
causing the front to veer west in this region. Since this
warm water is derived from the WSC it is reasonable to
assume that the postion of the front north of 78°N will vary
somewhat with the strength of the WSC. Aagaard and Coachman
(1968a, p. 197), citing the work of Soviet oceanographers ,
note that there are strong seasonal fluctuations in the
strength of the WSC and such fluctuations are probably
reflected in the behaviour of the EGC (although the nature
of the coupling between the two is open to debate).

3 . The Return Atlantic Current

In most of the frontal transects, a warm filament of
dilute AW (i.e. >3.0°C, <34.9) is found close to the main

42

thermal expression of the front between 100 m and 25 m.
Transects 1 (Fig. 3.4) and 3 (Fig. 3.6) show good examples
of this. In Fig. 3.6a filament of AW is separated by AIW
from AW of similar characteristics lying some 30 km farther
east. The filaments are often substantial in size - up to
200 m in thickness and 20 km in horizontal extent - as
defined by the 3°C isotherm. The north-south dimensions of
the filaments are undefined. These filaments appear to be
embedded in the core of RAC water described by Paquette et
al (1985, p. 4869) from the NORTHWIND early winter 1981 data
although in none of the transects from that cruise were
temperatures found as high as those noted in the present
cruise. A temperature-salinity (T/S) plot (Fig. 3.3) of
some of the stations at which this feature was noted, from
79°55N (Station 23) southward along the front to 77°15N
(Station 280), shows that the water characteristics of this
core vary somewhat with latitude. The salinity of the core
generally decreases with latitude and, after an initial
increase in temperature at Station 23, the temperature
maximum also decreases with latitude. However, there is no
indication whether the core is continuous or fragmented over
this range.

The variation in maximum temperature of this core is
also indicated in Table II. The maximum temperature of the
core initially rises from 4.9°C at 80°N to 5.8°C at 78°10'N
after which it decreases to 3.9°C at 75°44'N. Not surpris-
ingly, the east-west thermal gradient at the front, measured
at 50 m, also follows this trend with maximum values noted
between 78°48N and 77°15'N and thereafter decreasing south-
ward. The initially lower temperature at 80°N might be
expected if one assumes that the westward flowing arm of the
WSC has a north- south temperature gradient with maximum
temperatures close to the zonal ice edge in Fram Strait. At
80°N, the westward flowing water comes from under the ice

43

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44

while at 79°N - 78°N it comes from the warmest portion of
this westward flow.

The warm core of RAC water, found close to the front
in most of the frontal transects presented here, was also
observed during other cruises. Data from NORTHWIND 1981
showed the core cooling from >3°C at 78°N to >2.5°N at 76°N
and fragmented farther southward. A 79°N frontal transect
from the 1979 WESTWIND cruise (Newton and Piper, 1981) shows
a large (>2°C) core extending from 150 m to the surface
lying close to the eastern side of the EGPF. The core
temperature was reduced considerably in the 78°N frontal
transect conducted later in the cruise.

The variation in temperature with latitude of this
warm core is consistent with the hypothesis that the
majority of the input of AW into the RAC comes from the
westward turning arm of the WSC above 78°N. If this is so,
then presumably this input water is subjected to atmospheric
cooling and mixing along the frontal region, thus reducing
the size of the high temperature core and its maximum
temperature, as observed. If, on the other hand, the west-
ward turning of the WSC occurred to a significant degree
over a broader range of latitudes, say from 75°N (at which
latitude, one would expect surface temperatures in the WSC
to be about 10°C), as suggested by Aagaard and Coachman
(1968b, p283), the temperature of the water immediately to
the east of the EGPF should increase with decreasing
latitude, a feature generally not observed.

To summarize, it is hypothesized that the WSC splits
into two sections near Svalbard, one of which turns westward
between about 78°N and 80°N, north of the dome of cooler
water which characterizes the central Greenland Sea. This
westward turning arm interacts with the southward moving
polar waters of the EGC influencing the position of the EGPF
and the ice margin in the region. Such an interaction may be

45

reflected in the slightly cooler maximum temperature of the
RAC noted in Transect 1 at 79°55'N than in transects immedi-
ately southward. This picture might be resolved by
conducting a transect north along the 5°E meridian through
Fram Strait on a future cruise.

4. Displacement of the Surf icial Front

The front north of 77°30'N is divided between a
lower portion from 200 to 25 m and a shallower surface
front. In Transects 1 (Fig. 3.4) and 3 (Fig. 3.6), the
surface front was not encountered and was displaced at least
30 km east of the subsurface position. Transect 6 (Fig. 3.9)
clearly shows the separate upper and lower fronts. South of
this transect, the surface expression of the front is either
weak or continuous with the subsurface portion.

This division of the front is probably due to the
large area of dilute surface water formed by the melting of
sea ice. At 77°30'N and southward, the ice edge becomes
considerably better defined and it closely follows the shelf
break contours. To the north, the melting of sea ice has
been more extensive, possibly as a result of the advection
of warm AW from the WSC onto the northern shelf, resulting
in an expanse of cool dilute surface water.

The location of the surface expression of the EGPF
is probably primarily influenced by the growth or retreat of
the ice margin. An example of such a process might be the
action of offshore winds which blow substantial quantities
of ice seaward into warmer water, causing the ice to melt,
cooling and diluting a large expanse of surface water.
Since the ice edge can move faster than the front due to the
inertia of the water, the effect is seen as a shallow
surface front displaced seaward of the subsurface front.
This same type of displacement can occur in a region of
rapid ice growth. Perdue (1981, p. 38) shows several

46

transects in the region of 76°30'N to 78°N from the
NORTHWIND autumn 1981 cruise in which the surface expression
of the front was extended 20 - 40 km seaward of the lower
part. He ascribed this extension of the front to the rapid
expansion of the ice margin followed by a retreat, leaving a
layer of PW to the east. Presumably this PW was initially
AIW which had been conditioned by the melting process.

5 . Fine structure

Some notable examples of f inestructure can be seen
in a few of the transects from the NORTHWIND 1984 cruise.
Transect 12 (Fig. 3.15) at 76°N is an example of a frontal
crossing in which the f inestructure is so highly developed
that the precise location of the front is obscured.
Generally the f inestructure observed was limited to the
frontal region and usually became more developed in the
southern transects (little or none was noted in Transects 1
through 4, for example). Finestructure primarily consisted
of an interleaving of AIW and PW, generally in the upper
100 m immediately east of the EGPF. Considerable temperature
fluctuations over a short vertical distance were noted in
some instances. For example, near the 60 m depth at Station
320 in Transect 12 (Fig. 3.15), the temperature varied from
-1.5°C to 2.0°C and back again over 24 m. Presumably fine-
structure of this nature could be formed by AIW at or near
the surface being cooled east of the EGPF and descending
westward along an isopycnal into the region of the front.
The finestructure was more developed to the south where the
ice in the MIZ was more dense. The patchwork of open water
and floes of melting ice in this region could generate
parcels of water near the front with different salinity and
temperature characteristics but similar densities.

Paquette et al. (1985, p. 4879) present a descrip-
tion of finestructure along the EGPF as noted during the

47

autumn 1981 NORTHWIND cruise. Based on an analysis of the
fluxes and dynamics involved, they estimated the lifetimes
and mean sizes of the f inestructure elements. Finestructure
observed during that cruise consisted of elements with peak
to peak temperatures in excess of 1.0°C associated with the
AIW along the front at depths just below the temperature
maximum. Temperature- salinity cross- sect ions from the 1981
data show finestructure generally located between 70 and
300 m in the AIW sandwiched between lines of constant
salinity. They proposed that finestructure consists of fila-
ments of anomalously warm or cool water with a mean length
of 27 km in the along front direction. Given this, it is
understandable that the 45° orientation of Transect 12 in
1984 with respect to the front would exaggerate the appear-
ance of the finestructure elements compared to the other
transects in the region which are positioned normal to the
front .

Finestructure noted during the 1984 cruise generally
followed this pattern. Transects 7 (Fig. 3.10) and 6
(Fig. 3.9) provide examples of interleaving layers of AIW
between 50 and 300 m, generally confined between the 34.7
and 34.9 isohalines. However, the horizontal extent of the
development of this finestructure is not as great as that
noted in the transects presented for the 1981 cruise in
which lenses of AIW warmer than 1.5°C were noted under the
PW up to 90 km west of the front.

In none of the transects published from the 1981
NORTHWIND cruise (Paquette et al . , 1985; Perdue 1982) is
there any notable finestructure development consisting of
AIW in the PW fraction immediately to the west of the front.
This, however is noted fairly frequently in several of the
frontal transects developed from the 1984 data. For example,
a lens of AIW at 60 m depth located 20 km west of the front
is imbedded in the PW layer in Transect 11 (Fig. 3.14),

48

while in Transect 12 (Fig. 3.15), the PW fraction near the
front contains AIW f inestructure lenses up to 50 km west of
the front. Finestructure in the PW layer was observed in
several stations taken near the EGPF at the mouth of Belgica
Trough in the early fall of 1979 (Newton and Piper, 1981).
These show significant AIW interleaving with the PW layer
between 75 and 20 m.

6 . Mesoscale Features

A striking example of a larger scale interleaving of
PW and AIW was noted in Transect 5 (Fig. 3.8) along 77°54'N.
The front, as defined at Transects 4 and 6, lies close to
the 5°W meridian which runs between Stations 206 and 205 in
Transect 5. The extrusion of cold water seen in this tran-
sect extends some 20 km beyond the presumed location of the
front and is sandwiched between the 33.5 and 34.5 isoha-
lines. The form of this extrusion is reminiscent of an eddy
about to be detached. But because the isopycnals in the
upper 150 m rise monotonically from west to east (and are
almost horizontal across the extrusion itself), the mass
distribution is not indicative of an eddy-like rotation (see
also Section 8 in Fig. 3.43).

A significant displacement of isotherms and isoha-
lines appears to have occurred in the AIW layer at Station
28 in Transect 1 (Fig. 3.4). As indicated in the vertical
contours of baroclinic velocity shown in Section 1 of
Fig. 3.41, the distortion in the mass field at this location
may be suggestive of a weak eddy-like rotation. If this
feature does represent an eddy, it would be an anticyclonic
one with a radius of about 15 km, comparable to a typical
Rossby radius of deformation at this latitude. Similar
features were also noted during the WESTWIND 1979 (Newton,
in preparation) and NORTHWIND 1981 (Paquettte et al., 1985,
p. 4870) cruises.

49

7 . Frontal Variability

Two transects, 9a (Fig. 3.12) and 10 (Fig. 3.13),
were made three days apart across the same section of the
front adjacent to the entrance to Belgica Trough. These
transects were separated by no more than 3 km and provided
an opportunity to observe the temporal variability of the
EGPF in this area. A comparison of these two transects
indicates that the surface expression of the front and the
region of its initial upward development at 150 m are coin-
cident in each crossing. However, between 11 and 14
September, the front itself changed shape from concave to
convex, the portion at 50 m bowing eastward some 25 km. Also
at 200 m, the 2°C isotherm has been displaced westward some-
what and its vertical development shortened. Additionally,
cold (<0°C), saline (34.88) water, characteristic of GSDW is
observed as shallow as 300 m at Station 266 in 11 September
but is absent in the 14 September transect.

The EGPF has been frequently noted to vary in posi-
tion over relatively short periods of time. Aagaard and
Coachman (1968b, p. 272), reviewing a sequence of stations
occupied by EDISTO in 1965 at 73°N, noted a lateral fluctua-
tion in excess of 90 km in the position of the front. They
speculated that large scale eddies or a variation in inten-
sity of the circulation in the Greenland Sea may be
responsible .

50

STA HO

K>0

DISTANCE (Kn

Figure 3 . A

Transect 1 along 79 55'N. In this transect, the
front is shown displaced about 120 km east of
the shelf break. In this figure and in all
succeeding transects, isotherms are shown as
solid lines and isohalines as dashed lines. The
vertical scale of this figure is compressed to
show the water properties below 500 m.

51

141 140
_ STA No . ,
0 i — — ' *r

147 146 149

100 120

DISTANCE (Km)

Figure 3.5 Transect

The EGPF was not

2 along 79°12'N.
included in this transect but the upward turning
of the isopleths at Station 151 suggest that the

ront is probably located within 50 km of the

helf break at this latitude.

52

170 171 17?

100 120 140

DISTANCE (Kn>)

Figure 3 . 6

Transect 3 along 78°46'N. The subsurface
expression of the EGPF is located 18 km east of
the shelf break. A warm filament of AW.
separated by more than 20 km from water of
similar properties, lies close to the east side
of the EGPF.

53

X

c

oj

PQ

cOPn

OCX,

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OOJ

rH

0J OJ

PQ.fi

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m

o co

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lH

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54

^'°l\

20 30

DISTANCE (Kn

Figure 3.8

Transect 5 along 77°50'N. This transect shows
the horizontal extrusion of PW some 20 km east
of the EGPF possibly developing into an eddy.
The horizontal scale of this figure has been
expanded for clarity.

55

200
1

40 60

DISTANCE (Km)

Figure 3.9 Transect 6 along 77°30'N. In this transect the
EGPF is split into an upper and lower front.

56

279 280 281

40 60
DISTANCE (Km)

Figure 3.10 Transect 7 along 77°15'N

57

292 293 29* 295 296 297

40 60

DISTANCE (Km)

Figure 3.11 Transect 8 along 76°50'N

26' 262 263

264 265 266

40 60 80

DISTANCE (Km)

Figure 3 . 12

Transect 9a at 76°30'N at the mouth of Belgica
Trough. Compare this transect with Transect 10
(Figure 3.13) made 3 days later. Cold saline
water is evident at depths below 300 m at
Station 266 .

59

308 307 306 303 309 304

20 40

DISTANCE (Km)

Figure 3.13 Transect 10 at the mouth of Belgica Trough. The
shape of the EGPF has changed and the cold deep
water noted in Figure 3.12 is not evident here.

60

20 40

DISTANCE (Km I

Figure 3.14 Transect 11 at 76°15'N. Some f inestructure
consisting of AIW in the PW layer is evident.

61

„.W. 525 524 525 522 521 520 519 518 517 516 515

STA No , , ■ ■ ' ' , ' I ' ' *

,<-\T >

0 ov^>-

J_- '-' 0' > 2 0*

?^i5T^^s^^^oTV^^> 5 0.

--■I V ^r^\^^FsH^^^'
55 0%.--- _ ^?^o3S^5^^

55 5%. >I0*^^^^2 0»"

,^

~ 15-

0 °'^y//'/y^ « 2 0- • ,
54 7%. / //

2 0*

Figure 3.15 Transect 12 along 76°00'N. In this transect,

oriented 45

development is extensive

to the EGPF, f inestructure

62

NW SE

_,. . 323 326 327 328 329 330 331 332 333

STA "" I I J 1 1__J I

20 40

DISTANCE ( Km )

Figure 3.16 Transect 13 at 75°42'N

63

C. THE CONTINENTAL SHELF

1 . Introduction

NORTHWIND completed ten transects of the shelf in
the vicinity of Belgica Bank as well as several transverse
crossings of Belgica Trough, Norske Trough, and Westwind
Trough. Transects were also constructed from stations taken
along the axes of these troughs. The location of transects
made on the shelf is shown in Fig. 3.1; those made in the
troughs are shown in Fig. 3.17.

The waters of the continental shelf consist prima-
rily of PW more or less conditioned by local processes.
These include sea ice melting and freezing, surface radia-
tion cooling and insolation, and dilution by continental
run-off and the melting of glacial ice, particularly near
the northern fjords. The lower boundary of the PW on the
shelf remains, for the most part at about 200 m, thinning to
about 150 m near the shelf break at 76°N.

This next sub-section will first present a brief
description of the oceanographic features of the major areas
on the northern shelf, i.e., the above named troughs and
bank. Following sub-sections provide an expanded description
of shelf water properties using a T/S diagram and horizontal
plots of water characteristic distributions.

2 . Regional Hydrography

a. Belgica Bank

Crossings which covered Belgica Bank are included
in Transects 2 to 5 in Section B of this chapter (Figs. 3.5
- 3.8). The bank extends eastward from a crest (which at
Northwind Shoal becomes as shallow as 15 m) to the shelf
break some 180 km further east. PW is the dominant water
over the bank occupying the upper 200 to 225 m in the west
(where the bottom is deep enough) shoaling to about 150 m at
the shelf break.

64

20 w L

5 E

lb w

10 w

5 W

Figure 3.17 A map showing the location of transects
conducted over the troughs which cut across the
northeast Greenland shelf.

65

Underlying the PW, in areas where the shelf is
deep enough to accommodate it, is the AIW layer. The latter
extends as far inland as 50 km west of the shelf break in
the north and 100 km farther south. AIW is also found in
pockets at the bottom of the trough east of the crest of
Belgica Bank. The maximum temperature and salinity of this
layer occurs close to the bottom on the bank so that AIW
with the highest salinities and temperatures (generally not
more than 34.8 and 1°C, respectively) are found over the
deepest portions of the bank (see, for example, Figs. 3.34
and 3.35 compared to Fig. 2.2).

b. Belgica Trough

NORTHWIND made a series of four transverse cross-
ings of Belgica Trough about 50 km apart (Transects 14 - 17
in Figs. 3.19 - 3.22). However, the development of water
properties in this trough can best be seen in an axial tran-
sect (Transect 9, Fig. 3.18) constructed from stations
occupied over a 3.5 day period.

Generally, temperature and salinity isopleths
deepen to the west. This is, to some extent, more noticeable
in the water below 100 m and is not inconsistent with what
might be expected from a westward movement of AIW from the
frontal region up the trough. The PW layer thickens from
less than 150 m at the entrance of the trough to 220 m at
its western end. Between Station 258 and 259 (Fig. 3.18) the
salinity of the lower -1.5°C isotherm changes sharply from
almost 34.0 to less than 33.5, suggesting that the cold
saline fraction of PW discussed in Section B of this chapter
has penetrated 60 km down the trough compared to its rela-
tively minimal invasion onto Belgica Bank (see Transect 3,
Fig. 3.6 for a comparative example). Pockets of this cold
fraction can also be seen farther into the trough at
Stations 245 and 231. Another feature of the PW layer is a

66

lens of water warmer than -1.0°C centered at 25 m imbedded
in cooler water and which extends throughout much of the
length and breadth of the trough (see Figs. 3.18 and 3.21).
This lens might be a remnant of summer warming and fresh-
ening by ice melt with the waters above being cooled some-
what due to the onset of fall or cooling by the passage of a
melting ice floe. However, with the exception of Westwind
Trough, this feature was observed nowhere else to such a
degree on the shelf.

About half way along the trough, the PW at 65 m
cools to -1.7°C in a 15 m thick band generally centered over
the deepest areas. Within this band, the temperature
decreased to -1.81°C at Station 257 (located 24 km south of
Station 258 in Fig. 3.18), the coldest water encountered
anywhere during this cruise. Further comments on the distri-
bution and nature of this band of water are made in Section
C of this chapter in conjunction with Fig. 3.30.

About half of the water mass in the trough
consists of AIW which becomes cooler and less saline towards
the northwest. Water with temperatures greater than 1°C and
salinities exceeding 34.9 lie close to the bottom along
almost the entire length of the trough.

c. Norske Trough

At its western end, Belgica Trough merges with
Norske Trough which parallels the coast northward. Complete
transverse sections of much of Norske Trough could not be
completed due to the presence of fast ice which covered its
western boundary. A partial crossing of the southern portion
of the trough can be seen in the western part of Transect 4
(Fig. 3.7) and a complete crossing of the northern part in
Transect 19 (Fig. 3.24). A non-synoptic axial transect
(Transect 18, Fig. 3.23) presents some idea of the character
of the water in this deep coastal depression.

67

The PW layer extends to 200 m at the southern
extremity of Norske Trough becoming somewhat thinner (175 m)
at its northern end. A temperature minimum is also present
in this trough with values less than -1.7°C centered at
about 75 m in the south. This water has similar salinity
characteristics to the temperature minimum described earlier
in Belgica Trough - about 32.3 to 32.5 (see, for example
Fig. 3.29). In the northern end of Norske Trough the -1.7°C
layer band is found at about 60 m. It is comprised of some-
what less saline water, lying almost exclusively between the
32.1 and 32.3 isohalines, and is thicker than the -1.7°C
band at the southern end. At Station 120 in Fig. 3.23 the
two layers of cold water can be seen to overlap.

The AIW layer decreases in salinity and tempera-
ture towards the north. The maximum temperature and salinity
in the water column is found near the bottom. With the
exception of the extreme southern end, it is cooler than 1°C
and fresher than 34.9.

d. Westwind Trough

At 80°30'N Norske Trough connects with Westwind
Trough, an apparent extension of Ingolf's Fjord. As seen in
the axial transect of Westwind Trough (Transect 23, Fig.
3.28), the 180 m thick PW layer has the same characteristics
as in the northern portion of Norske Trough with the excep-
tion that the near-surface "warm" layer, described in
connection with the Belgica Trough PW, is also present here.
The -1.7°C layer is defined by the 32.1 and 32.3 isohalines
similar to that in the northern portion of Norske Trough.

The AIW layer is relatively cool and fresh
compared to its properties in Belgica Trough. Compare, for
example, Transect 23, Fig. 3.28 with Transect 9, Fig. 3.18
or the reflection of the properties of the AIW at the bottom
as presented in Figs. 3.34 and 3.35. Maximum temperatures

68

are about 0.5°C and salinities are about 34.8. Given that
the 34.8 isohalines in Westwind Trough and Belgica Trough
are generally at the same depth (about 240 m) , the differ-
ence in bottom characteristics is probably, in part, a
reflection of the greater depth of Belgica Trough. However,
as Fig. 3.4 shows, stations immediately seaward of Westwind
Trough (e.g. , 31, 32) did not show any salinities in excess
of 34.9, even at depths in excess of 800 m. The somewhat
cooler and more dilute AIW in Westwind Trough compared to
that found at the bottom of Belgica Trough may also, there-
fore, be a reflection of the fact that the RAC , which is
probably the source of warm (>1°C), saline water in both
troughs, is located some 100 km farther seaward of the
entrance to Westwind Trough than it is at the entrance to
Belgica Trough.

69

00
3
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.-t
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70

SW

200

256 255 254 253

-1 1 I L_

NE

40 60

OISTANCE (Km)

Figure 3 . 19

Transect 14 across Belgica
transect is located about 65
entrance to Belgica Trough.

Trough. This
km west of the

71

sw

J I 0%
12 0*.

245

1

NE

40 60 80

DISTANCE (Km)

Figure 3.20

Transect 15 across Belgica Trough. This
transect is located about 125 km west of the
entrance to Belgica Trough.

72

40 60 BO

DISTANCE (Kn>)

Figure 3.21

Transect 16 across Belgica Trough. This
transect is located about 190 km west of the
entrance to Belgica Trough.

73

300

400

40 60

OISTANCE (Km)

Figure 3.22

Transect 17 across Belgica Trough. This
transect is located about 250 km west of the
entrance to Belgica Trough.

74

u

o

V •

o

4-1 CN

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Ol-H

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80 100

DISTANCE (Km)

140 160

Figure 3.24 Transect 19 across the northern end of Norske
Trough.

76

81 80

200
?

300 \-

30 «0 50

DISTANCE (Km]

Figure 3 . 25

Transect 20 extending eastward from Ingolf's
Fjord to Westwind Trough.

77

10 20

DISTANCE (Km)

Figure 3 . 26

Transect 21 across Westwind Trough. This
transect is located 150 km west of the entrance
to Westwind Trough. In the northern portion of
the shelf, the -1.7° C water was confined to
the troughs .

78

SO 40 30

DISTANCE ( Km )

Figure 3.27

Transect
transect
Westwind
trough .

22 across Westwind Trough. This

located 95 km west of the entrance to

Trough, does not completely cross the

79

XX

\^'<^^

60 80

distance: (««

Figure 3.28

Transect 23 along the axis of Westwind Trough.
The -1.7° C water at Station 32 is slightly
more saline than that farther east. Surface
waters here are warmer than at more southerly
locations on the shelf.

80

3 . Shelf Water Masses

A comparative look at the relationship of water
properties on the shelf is presented in the T/S plot shown
in Fig. 3.29. Two stations (24 and 307) located east of the
shelf and just west of the EGPF are also included for
comparison. The figure includes Station 245 from the middle
of Belgica Trough, Station 184 at the southern end of Norske
Trough, Station 182 in the middle of Norske Trough, Station
120 at the northern end of Norske Trough and Station 37 in
Westwind Trough. (Transects containing these stations may be
found in Figs. 3.18, 3.23, and 3.28). Station 137, a
typical shelf station taken over the middle of Belgica Bank
is also included.

This temperature- salinity plot presents a consistent
picture of the evolution of water properties in meridional
and zonal directions. In general, cold low-salinity water is
present everywhere with a temperature minimum located at
about 75 m. A cold high- salinity (34.0) fraction is present
only at the EGPF with the exception of Station 245. As
noted previously, and in Fig. 3. 18, water of this character
extends westward into much of Belgica Trough. All stations
at which the depth is sufficient show some admixture of
AIW/AW as indicated by a rise toward the T-S peak. This peak
is best developed in the front itself and decreases in
maximum temperature toward the south. Such a maximum is not
reached in shallower stations. The near-surface temperature
maximum is scattered but is generally associated with
relatively warm water, both above and below.

a. Polar Water

An interesting feature of the shelf PW is that
despite the greater source of heat inherent in the rela-
tively large volume of AIW in the trough areas as compared
to the shallow bank waters, the coldest temperature water

81

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82

west of the shelf break is almost exclusively found in the
troughs. This is evident in a number of the transects
presented previously for the shelf (see for example, Figs.
3.20, 3.24 and 3.26) where water colder than -1.7°C is found
only over the trough areas. Generally, this cold water
layer does not seem to have advected onto the adjacent banks
in the north, despite the fact that this layer is located
shallower than the bottom of the bank. This feature is most
evident in Fig. 3.30 where the thickness of the <-1.7°C
layer has been contoured in 15 m intervals. The -1.7°C water
is particularly clearly associated with deeper water in the
northern portion of Norske Trough and in Westwind Trough
where, as previously noted, it is bounded almost precisely
by the 32.1 and 32.3 isohalines. Farther south, over Belgica
Trough and the surrounding bank waters, the cold layer is
somewhat more saline (32.3 - 32.5) while to the east, in the
frontal region, the -1.7°C water had variable salinities
from 32.3 to 32.9. At the front near 80°N, the more saline
water discussed earlier achieved temperatures lower than
-1.7°C and is contoured in Fig. 3.30 as an underlying
layer.

The basic structure of the PW has been described
and accounted for by other authors. For example, Aagaard and
Coachman (1968b, p. 277) describe the temperature minimum
found in the summer PW layer at 50 m as a result of the
warming and freshening of the surface layer above by insola-
tion and ice melt and present an example of it from the 1965
EDISTO results. Newton and Piper (1981, p. 22), in
discussing the WESTWIND 1979 results, noted that except for
warming at the top by insolation and the bottom by the AIW
layer, respectively, the PW consisted of a cold water mass
of fairly uniform salinity. They noted a relatively large
amount of water concentrated in a salinity range of 33.2 to
33.4 at the temperature minimum, a considerably greater

83

20 W

\t w

5 W

a i%.-32 j%.

52 5%. -5! 6 %,

52 5%.- 52 »%.

55 e*.. -54 0%.

Figure 3.30

A plot contouring the thickness of the -1.7° C
layer in 15 m intervals. Over the shelf, water
of this temperature is generally confined to
the deeper areas, particularly in the north.
Salinity ranges are shown by the contour line
pattern as indicated.

84

value than the 32.1 - 32.5 noted for the <-1.7°C water on
the shelf observed in 1984. This appears to be a result of
the greater freezing stress experienced in 1979 or perhaps
to the presence of warmer, more dilute waters during the
1983/84 freezing cycle and reflected in the lower degree of
ice coverage during the summer of 1984.

The surface properties of the shelf and frontal
waters may also serve as useful indicators of local
processes and advection. In general, the distribution of
various water properties on and adjacent to the shelf
appears to be primarily affected by proximity to the coast
and the EGPF, bathymetry, circulation and, in the case of
surface properties, reflects the ice concentration. For
example, a plot of surface temperatures (Fig. 3.31) and a
plot of the surface temperature as a function of the
freezing point (Fig. 3.32) both clearly show the location of
the EGPF. Isotherms are particularly densly packed near the
mouth of Belgica Trough, a region where the gradient of ice
concentration (Fig. 2.3) is also particularly steep. Surface
temperatures in the northern portion of the shelf are
slightly warmer than they are in the region near Belgica
Trough, consistent with the lower ice concentrations in the
north.

The surface salinity distribution (Fig. 3.33)
shows the effect of coastal fresh water input and reflects
some bathymetric features. For example, the surface water
overlying Belgica Trough, Westwind Trough and possibly most
of Norske Trough is, at <30.0, fresher than the surface
water overlying the adjacent banks to the east. The shape of
the 30.0 isohaline over Westwind Trough is suggestive of an
eastward advection of low salinity water there. A local
surface salinity high overlies the shallowest portion of
Belgica Bank while a region of low salinity overlies the
central portion of the bank. Isohalines are packed

85

relatively closely at the shelf break, reflecting the posi-
tion of the EGPF.

A comparison of the above plots of surface prop-
erties with those developed from the WESTWIND 1979 cruise,
shows some interesting similarities and differences. The
plot of surface temperatures referenced to the freezing
point (Newton, in preparation) from the 1979 data, also
shows warmer surface temperatures over the northern shelf
compared to the southern portion. Overall surface tempera-
ture values were lower than those in Fig. 3.32, while
surface salinity values were about 1 ppt higher - reflecting
the lighter ice concentrations in 1984. However, the
isopleths of surface temperatures and salinities for the
1979 data which parallel the EGPF show a significant west-
ward turning at about 77°N, just north of the entrance to
Belgica Trough. This feature is not evident in Figs. 3.32 or
3.33 and may reflect a fluctuation in circulation in this
region.

b. AIW

As pointed out with reference to the shelf
temperature- salinity transects presented earlier, AIW is
found in all trough areas and over the deeper parts of the
shelf. The distribution of bottom temperatures (as devia-
tions from freezing) and salinities are shown in Figs. 3.34
and 3.35. Values were available only for the shelf areas
(since no CTD casts were made to the bottom east of the
shelf break) and generally reflect near maximum temperatures
and salinities for the AIW on the shelf. The warmest and
most saline waters on the shelf are found along the axis of
Belgica Trough, the southern part of Norske Trough and, to a
lesser extent, along the axis of Westwind Trough. Where
bottom topographic features extend up into the PW layer,
both salinities and temperatures decrease, particularly over

86

20 W

M W

Figure 3.31

Temperature
clearly show
temperatures

of the surface layer. Isotherms
the position of the EGPF. (Warmest
over the shelf are near Ob' Bank.

87

\b w

10 W

b W

Figure 3.34

Temperature deviation from freezing at the
bottom. Values reflect bathymetry and suggest
that the warm water in Belgica Trough, Norske
Trough, and Westwind Trough probably advected
from the east .

88

20 W

15 W

10 w

5 W

Figure 3.33

Salinity of the surface layer. Salinities over
the central shelf are low. The configuration of
the 30.0 isohaline over Westwind Trough
suggests a westward flow.

89

the crest of Belgica Bank. The distribution of bottom water
properties suggests that AIW is intruding under the PW up
the troughs from the east, both at Westwind Trough and
Belgica Trough since there is no apparent source of such
warm saline water on the shelf.

D. CIRCULATION AND TRANSPORT
1 . Introduction

Without reliable long-term current meter data, it is
difficult to make definitive statements about the absolute
movement of water, particularly over such a relatively wide,
shallow-water regime with rapidly varying bathymetry such as
exists on the northeast Greenland shelf. It is difficult to
make a good approximation of the barotropic component of the
current and indeed, frictional and boundary influences may
be significant, raising the question as to how geostrophic
the current in fact is.

The question of validity of dynamic heights obtained
by extrapolation in shallow water was considered by Reid and
Mantyla (1976). These authors extrapolated the slopes of
dynamic heights into shallow water regions rather than
projecting them horizontally as has been done here. In
comparing dynamic heights for coastal stations in relatively
shallow water with tide gauges and current measurements in
the North Pacific periphery, they found good agreement
between the tide gage measurements and dynamic heights and
between geostrophic currents and current measurements. This
appeared to be valid for time scales long enough for quasi-
geostrophic equilibrium to be achieved. In the area of their
study, this period was on the order of several days to
several weeks. For this reason, considerable reality is
expected from the baroclinic geostrophic currents computed
in the present work. Therefore, in the following sections,

90

2C w

it w

IU w

b W

Figure 3 . 32

Temperature departures from

in the surface layer. Minimum values are

over the southern shelf where the
concentration is high.

the freezing point

round

ice

91

20 W

lu W

5 W

Figure 3.35 Bottom salinity. High salinity water at the
bottom of the troughs has probably advected
from the east .

9?

the circulation of the EGC in the region of the EGPF and
over the shelf will be estimated, using the dynamic topog-
raphy, vertical baroclinic velocity cross- sections and the
distribution of water properties as a guide.

2 . Dynamic Topography

Surface dynamic heights were computed using the
methods outlined in Chapter 2 with reference to the 150 dbar
(Fig. 3.36), 200 dbar (Fig. 3.37), and the 500 dbar (Fig.
3.38) levels to assess the contribution that different
levels of assumed no net motion would make to the dynamic
height fields and to facilitate comparison with similar
profiles produced by previous authors. A plot of the 150
dbar surface relative to 500 dbar was also constructed (Fig.
3.39).

The surface dynamic height topographies show a
number of features in common. The obvious one is the high
gradient region representing the EGPF. In all three surface
plots, the maximum value of the gradient across the front
remains relatively constant between 81°N to 77°30'N,
suggesting baroclinic surface flows of 0.35 to 0.50 m/s. A
westward turning of the isobars occurs at 77°15'N, north of
the entrance to Belgica Trough, followed by a southward turn
indicative of southwesterly surface flow over the trough
itself. This is well developed in Figs. 3.36 and 3.37 but
is less evident in Fig. 3.38. At this point, the frontal
dynamic height gradient decreases to that which would
support a 0.25 m/s baroclinic flow.

In the region of the front, changing the level of no
net motion from 150 dbar or 200 dbar to 500 dbar made little
difference to the spacing of the isobars (compare Figs.
3.36, 3.37 and 3.38) and thus, implicitly, in the baroclinic
current flow. This suggests that little contribution to the
pressure gradient is made by the AIW found below 150 m, at
least in summer.

93

-» —

h

— v-

*»^

■»• Cl.C 10.0 20.0 30. t iO.O

CM/SCC

15 w

10 w

5 W

Figure 3.36

Surface dynamic topography referenced to 150
dbar in dynamic meters. A dynamic "hill" over
the center of the shelf suggests anticyclonic
circu lat ion.

94

\

—

—

O.C 20.0 30.0 10.0

CM/ sec

lC W

15 W

10 W

5 w

Figure 3.37 Surface dynamic topography referenced to 200
dbar in dynamic meters.

95

3:

U.O 10.0 10.0 30. C 40.0

Cfl/SEC

20 W

15 W

10 w

Figure 3.38 Surface dynamic topography referenced to 500
dbar in dynamic meters. The isobars over
Westwind Trough suggests eastward flow there.

96

. .._,

\

\

\

XI

1- —

—

_j— .

—

.0 SO 10.0 ISO 20.0 2S.0

HM/5EC

2C W

10 W

5 w

Figure 3.39 150 dbar dynamic topography referenced to 500
dbar. Hatched areas indicate bottom depths
less than 150 m.

97

Another dominant feature is the dynamic "hill" over
the central portion of Belgica Bank, which reflects the low
salinities in the water column in that area (See Figs. 3.33
and 3.35). This feature suggests an anticyclonic geostrophic
surface flow around and over the shallowest parts of the
shelf. A secondary high region, over Ob' Bank evident in
Figs. 3.36 and 3.37, implies a small region of anticyclonic
flow centered there too, but the main sense of the current
around 80°30'N, as implied by the dynamic topography, is
eastward along Westwind Trough.

Generally, the dynamic topography at 150 dbar, as
presented in Fig. 3.39 and contoured in 0.01 dynamic meter
intervals, mirrors that of the surface (Fig. 3.38). The
front is observed in the 150 dbar surface by a gradient
which would support a baroclinic current of 0.05 to
0.07 m/s, a seven-fold reduction from the surface values.
Over the shelf there is a generally southerly flow with
perhaps a few meanders. However, one can have little faith
in the large number of irregularities in the topography of
this surface, especially over the shelf, because a
contouring with a 0.01 dynamic meter spacing is approaching
the "noise" level of the technique.

Dynamic topographies developed from previous cruises
to the area show significant similarities to the features
shown in Figs. 3.36 - 3.39. The baroclinic features devel-
oped from the the EDISTO summer 1964 and 1965 cruises
(Aagaard and Coachman, 1968b, p. 279) show a strong gradient
at the EGPF indicating baroclinic geostrophic currents of up
to 0.23 m/s. Newton (in preparation), constructed a surface
dynamic topography chart, relative to 200 dbar of the front
and shelf regions based on the WESTWIND summer 1979 data. It
shows a significant gradient corresponding to a geostrophic
flow of about 0.3 m/s in the region of the EGPF and a
dynamic "hill" over the center of Belgica Bank (although the

98

WESTWIND 1979 data were sparse there and some interpolations
were indicated).

Paquette et al . (1985, p. 4876) developed dynamic
height contours in the region of the front for the surface
and the 150 dbar levels relative to 500 dbar from the
NORTHWIND autumn 1981 data, thus including the effects of
density gradients at greater depths than the two previous
analyses. Additionally, they showed that with closer station
spacing across the front, and a deeper reference level,
geostrophic baroclinic current velocities up to 0.96 m/s
(near 77°25'N) in the EGPF were evident. Their dynamic
topographies show isobars turning westward between 76°30'N
and 77°n at both the surface and 150 dbar levels suggesting
a bathymetrically steered flow towards the entrance to
Belgica Trough. This westward inflection of the isobars was
also evident in the 1979 dynamic topography (Newton, in
preparation) and is reflected in the westward turning of
isopleths of water properties at the entrance to Belgica
Trough also presented by Newton from the 1979 data. The
westward turning at the entrance to Belgica Trough, however,
is muted or non existant in Figs. 3.36 - 3.39. Instead, the
westward turning appears to take place north of the trough
entrance. Thus considerable fluctuation in the current flow
around the mouth of Belgica Trough can be expected (as
previously suggested by the comparison made in Figs. 3.12
and 3. 13) .

3 . Vertical Sections of Baroc linic Velocity

To further investigate the geostrophic current
velocity and volume transport along the front and over the
shelf, a sequence of vertical baroclinic current velocity
sections was constructed. Seventeen sections cover the shelf
break and, to varying degrees, the shelf; three were across
Belgica Trough and two across Westwind Trough. The location
of these sections is shown in Fig. 3.40.

99

15 rt

10 w

5 W

Figure 3.40 Location of vertical baroclinic current
velocity sections.

100

As indicated in Chapter 2, a reference level of 500
dbar was selected for Sections 1 to 16 with horizontal
extrapolation made for lesser bottom depths. Results of the
geostrophic and transport calculations are shown in Table
III.

Sections 1-16 are presented in Figs. 3.41 - 3.46.
Most sections were made along a line of latitude and are
arranged so that stations have the appropriate lateral
reference to the 10°W and 5°W meridians. Some sections
(those to the south where the EGC turns southwest) were made
at a 30° - 45° angle to the parallels making the vertical
stacking in the figures somewhat less accurate. Sections 1,
6, 7, 8, 9, and 11 covered significant portions of the front
and shelf, Sections 2-5 do not include the front, while
the remainder cover the frontal region only.

A sequential comparison of the sections reveals
several aspects of the flow over the front and the shelf:

• As indicated in Table III, there is only a moderate
variation in the maximum baroclinic current speed at the
front which is consistent with the relatively uniform
spacing of isobars of dynamic height noted in Figs. 3.36
- 3.38. Values varied from 0.30 to 0.47 m/s. The maximum
values were at the surface except in the two northern-
most frontal crossings (Sections 1 and 6) where peak
speeds occurred at 15 to 20 m below the surface.
However the salinity and density of the upper 5 m is
affected by the adventitious presence or absence of
melting ice which introduce anomalies on so short a time
scale that they are not geostrophically balanced. Thus,
baroclinic velocities in the upper 5 - 10 m of the
profiles may be suspect.

• A core representing a high speed jet was present in all
sections which crossed the EGPF. This core, as defined

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102

by a high velocity gradient, was typically less than 50
km in breadth and was confined generally to the upper
100 m in the region of the front. The core is occasion-
ally split into two (or possibly more) portions (Section
11, Fig. 3.44, is an example), up to 30 km apart,
indicating the filamental nature of the front.

• For those sections covering all or most of the front and
shelf (Sections 1, 6, 7, 9, 11), the southward baro-
clinic volume transport (defined as positive transport
in Table III) was about 1.6 Sv . A comparison of the
contribution of the total southward transport over the
shelf to the total transport (the difference between the
total southward transport and the off -shelf transport)
indicates that about 30 percent of the southerly trans-
port in Section 1 is carried by water west of the 400 m
isobath. In Sections 6, 7, 8, 9, and 11, this contribu-
tion rises to 40 - 60 percent. Such comparisons are
tenuous, however, because of the uncertainties inherent
in applying the Helland-Hansen technique over a wide
shelf such as this. In deep water the contribution of
layers deeper than 500 m to the baroclinicity has been
ignored. While this might create only a small error in
the computed surface velocities, the error in transports
could be substantial. Additionally, errors are intro-
duced because of the lack of ability to predict the
barotropic component, especially in shallow water. Thus
the figures given for surface velocities near the shelf
break are probably a bit low and the sign of the errors
in current velocities over portions of the shelf
considerably westward of the EGPF is indeterminate.

• Sections 13A and 13B (Fig. 3.45) were constructed from
the two lines of stations made three days apart and
oriented axially through the mouth of Belgica Trough in

103

Transects 9 and 10. In Section 13A, the core of the jet
has a considerably greater vertical development than in
Section 13B.

• In several sections which extended far enough west to
include it (Sections 1-6, 9), the northward flow of
water in the westward parts of the shelf can be seen.
Baroclinic current speeds here are up to 0.12 m/s with
maxima occurring 25 - 100 m below the surface. The
northerly transports, if accurate, are substantial - up
to 0.5 Sv - suggesting that a significant portion of
water in the northern part of the EGC recirculates
northward over the shelf, at least in summer.

In 1984 maximum baroclinic current speeds along the
front were reasonably constant with latitude, ranging from
0.30 to 0.47 m/s (Table III). No particular trend is obvious
and variations are probably reflections of instabilities
along the front. This fairly uniform behavior of the front
from 80°N to 75°45'N is consistent with the suggestion of
Paquette et al (1985, p. 4877) that the jet would probably
be observed at a high velocity all along the EGPF if the CTD
station density were high enough everywhere to resolve it.
The maximum current speeds in 1984 are intermediate between
the 0.80 to 0.96 m/s values computed from the autumn 1981
NORTHWIND cruise and the earlier EDISTO and WESTWIND values
quoted previously.

The total southward volume transport calculated from
the 1984 baroclinic measurements and integrated from the
front to as close to the coast as possible, varied from 1.25
to 1.86 Sv. Based on the NORTHWIND 1981 data, Paquette et
al., (1985, p. 4877) computed a transport of 1.2 Sv in the
region of the front. They also estimated a total southward
transport of 2 Sv from the ice edge to the coast by assuming
that the current velocity decreased linearly to zero towards

104

StoUon Number

SECTION 1

SECTION 2

SECTION 3

10°W

5°W

Figure 3.41

Sections 1-3. Solid isotachs indicate
southerly movement, dashed isotachs indicate
northerly movement. The high speed jet of the
EGPF is at Station 23 in Section 1. Northward
flowing water over the western portion of the
shelf can be seen at Station 121 in Section 2.
Sections 2 and 3 do not include the EGPF.
Section locations are shown in Fig. 3.40

105

SECTION 4

SECTION 5

SECTION 6

Station

Number

l« iU |4 IM ISO

a-

8-

■o 3

4-^/^o^>«*

> « -0.03 ^.

~~ ll>a-Ls' /^

S-

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= ?:

s

i

a

\

8-

\

a-
8

\

:00 £25 250

I

10°W

5°W

Figure 3.42 Sections 4
the EGPF.

6. Sections 4 and 5 do not include

106

StQtLOn Nombor

9 m n ZD

SECTION 7

SECTION 8

SECTION 9

10°W

5'W

Figure 3.43 Sections 7-9

107

Stetson Numbe

SECTION 10

SECTION 11

SECTION 12

10°W

5°W

Figure 3.44 Sections 10 - 12. The high speed iet is broken
into several filaments in Section 11.

108

SECTION 13A

SECTION 13B

10'W

5'W

Figure 3.45 Sections 13A and 13B at the mouth of Belgica
Trough. Note the change in vertical development
of the jet over 3 days.

109

Slal. or N.,nt,er

SECTION 14

SECTION 15

SECTION 16

-

/ -

I

i h

j

31

'* i

t. y^j

10'W

5'W

Figure 3.46 Sections 14 - 16. Meridional markings are
accurate for Section 15 only.

110

the land. Given that there is probably a significant north-
ward flow over the western half of the shelf , as implied by
Figs. 3.36 - 3.38, this assumption appears to be invalid.

The motion of AIW up the bottom of Belgica Trough is
not reflected in the dynamic topography or in vertical
sections of baroclinic velocity. The latter, shown in Fig.
3.47 in which stations on the axis of the trough (Stations
335, 245, and 252/253) are superposed, appear to reflect
local vortices such as that indicated by the "dynamic hill"
in the center of the trough indicated in Fig. 3.37. As
implied in this figure, the general sense of the baroclinic
circulation in the eastern portion of the Belgica Trough
area is southwesterly, although there may be some modifica-
tions to the flow producing some axial components in some
parts of the trough. Presumably then, the shoreward advec-
tion of AIW as suggested by the modification of water prop-
erties in Belgica Trough is too slow to be reflected in the
dynamic topography developed from the 1984 data or in winter
ice drift and reflects water movement on a longer time
scale .

Sections 20 and 21 (Fig. 3.48) are two transverse
sections across Westwind Trough about 50 km apart and devel-
oped with reference to 300 dbar. They are characterized by a
strong easterly baroclinic flow of water perpendicular to
the sections: 0.37 m/s at the surface near Ob' Bank in
Section 20 decreasing to 0.25 m/s at 40 m over the deepest
portion of Westwind Trough in Section 21. Transports of
about 0.5 Sv were calculated, suggesting that much of the
northward moving water in the western part of the shelf is
exhausted through Westwind Trough. This may contribute to
the injection of shelf - conditioned PW into the EGPF and also
contribute to the sightly lower salinities and temperatures
of the AIW immediately west of the shelf break at the
entrance to Westwind Trough compared to the AIW at the mouth
of Belgica Trough.

Ill

StalLO--. timber

SECTION 19

SECTION 18

• Hi :- \ .-le

SECTION 17

Figure 3.47

Sections 17 - 19 across Belgica Trough. The
solid isotachs indicate eastward flow. These
sections are are arranged so that the stations
on the axis of the trough are superposed.
Velocities in this figure are referenced to 300
dbar .

112

SECTION 20

-J

SECTION 21

Figure 3.48

Sections 20 - 21 across Westwind Trough. The
solid isotachs indicate eastward flow. These
sections are are arranged so that the stations
on the axis of the trough are superposed.

113

.4. Circulation

A map showing the circulation pattern inferred from
the information obtained during the NORTHWIND 1984 cruise is
presented in Fig. 3.49. As suggested by Newton (in prepara-
tion) , the surface circulation implied by the dynamic height
fields over the northern shelf is anticyclonic . A northward
flow in Norske Trough resulting from a clockwise turning of
the current around the southwest corner of Belgica Bank was
postulated by Kiilerich (1945, p. 32) based on a few
stations near lie de France and the southern portion of
Belgica Bank from the 1905 BELGICA expedition. He assumed
that this turning of the current in this region was respon-
sible for the ice-free water frequently observed near lie de
France (and also observed during NORTHWIND 1984) and for the
transport of driftwood northward.

That there is a significant northward component to
the surface current flow over the portion of the shelf
nearest the coast between 76°N and 80°N was confirmed by
observations of ice behaviour. The movement of several
large, readily identifiable ice floes during the period 22
August to 14 September 1985, in the vicinity of the fast ice
shelf from 77°30N to 79°30'N, was observed from a sequence
of NOAA 7 visual image photographs. During this period (in
which winds were generally light and variable) the ice moved
northward at about 2 km/day. This drift is consistent with
the direction and magnitude of the flow provided by dynamic
topographies .

Other observations of ice movement are consistent
with the circulation pattern discussed in this section.
Vinje (1978) tracked a number of buoys located on ice flows
from the Nimbus 7 satellite in 1976. The tracks of these
buoys are shown in the upper map in Fig. 3.50. The western-
most buoy appears to closely follow the course of Westwind

114

Trough; its average velocity from 31 August to 16 September
is about 0.12 m/s. Vinje (1977) also observed the movement
of ice from LANDSAT imagery in May and June 1976 (lower map
Fig. 3.50). He suggested that this ice movement, during a
period of relatively calm weather, probably reflects the
local oceanographic circulation, consistent with the anticy-
clonic circulation pattern observed in this area by previous
authors (Riis-Cristensen, 1938; Laktionov et al., 1960)

Kiilerich (1945, p. 27) also indicated a northward
flow along the shore of water derived from the westward
turning of a portion of the EGC up a trough south of Belgica
Trough at 76°N. If this additional shorebound current
exists, it might join the northward flow of water over
Norkse Trough, reinforcing it.

Some interannual fluctuations in the circulation
pattern are evident. As previously indicated, dynamic
topography from the 1981 and 1979 NORTHWIND cruises and
distribution of surface water characteristics from the 1979
data suggest a westward inflection of the EGC at the
northern entrance to Belgica Dyb , while the 1984 data indi-
cate that such a turning occurs farther north and farther
westward. Certainly the presence of relatively warm AIW at
the bottom of Belgica Trough and the intrusion of the cold
saline fraction normally noted only at the front some
distance down the trough (Fig. 3.18) indicated some sort of
axial flow but its strength and consistency are not well
established here.

115

Figure 3.49 Estimated circulation pattern over the shelf
and at the adjacent EGPF.

116

. \ . 1 . . -

Figure 3.50 Two maps (after Vinje, 1977) indicating ice
movement in 1976. The upper map indicates
movement of buoys located on ice floes in
August /September and tracked by the NIMBUS 7
satellite. The lower shows ice movement in May
and June deduced from LANDAT imagery.

117

IV. CONCLUSIONS

The waters of the East Greenland Current both in the
region of the front and over the adjacent continental shelf
from 75°45'N to 81°20'N have been examined using a rela-
tively dense network of CTD stations taken during the
NORTHWIND 1984 cruise. Baroclinic geostrophic transport and
current flow based on the distribution of water properties
and dynamic topography were developed with the following
major conclusions drawn:

• A number of characteristics of the EGPF observed by
previous authors were also noted during the 1984 cruise.
The front consisted of a marked east-west gradient in
salinity and temperature giving rise to a baroclinic
frontal jet with velocities of 0.30 to 0.47 m/s.
Considerable f inestructure development was noted in the
southern portions of the front often consisting of
parcels of AIW imbedded in the PW of the EGC surface
layer. A warm core of the RAC was found pressed close
against the eastern boundary of the front which often
included filaments of slightly dilute AW.

• The EGPF approached the continental shelf break from a
distance of 120 km at 80°N to 20 km at 78°48'N, after
which it paralleled the 400 m isobath south to at least
75°45'N. The latitude at which the EGPF closes the
shelf varies somewhat from year to year and may be a
function of fluctuations in the WSC as well as
interannual climatic variations.

• The warm core of RAC water found close to the east side
of the EGPF cools significantly at latitudes below 78°N,

118

suggesting that the majority of the input from the west-
ward turning arm of the WSC is made north of that
latitude .

• Southward volume transports were about 1.6 Sv . This
figure is, no doubt, a minimum since there is presumably
a significant contribution to the mass transport made by
the large volume of more slowly moving water below the
500 dbar reference level used.

• Circulation on the shelf between 76°N and 80°N is domi-
nated by a large anticyclonic gyre centered over the
shallowest portions of the shelf. Transports within this
gyre can be significant, with up to 0.5 Sv (or more) of
water moving northward on the western portion of the
shelf.

• The surface and bottom water characteristics and dynamic
height topographies developed suggest that water advects
westward at the bottom of the entrances to Belgica and
Westwind Troughs. Flow at the surface of Belgica Trough
is generally southward, perhaps with local modifica-
tions, while in Westwind Trough the surface flow is
eastward and southeastward.

119

APPENDIX A
MOLLOY DEEP

A large (60 km diameter) cyclonic ice and water eddy has
frequently been noted on the eastern edge of the East
Greenland Current at about 79°40'N, 001°E and described by
various authors (Vinje, 1977; Wadhams , 1979; Wadhams and
Squire, 1983). This eddy, which consists of relatively warm
near-surface water at its center, is marked by a character-
istic ice feature characterized by Wadhams and Squire (1983,
p. 2770) as a "backward breaking wave shape". The feature is
shown in Fig. A.l (after Smith et al . , 1984) which depicts
the ice edge observed in August 1980 (Wadhams and Squire,
1983) and May 1976 (Vinje, 1977) superimposed on a map of
local bathymetry (Perry et al., 1980).

The mechanism for the formation of this eddy has been
the subject of some speculation. Wadhams and Squire (1983,
p. 2776) argued that the East Greenland Current is baroclin-
ically unstable and presented a two layer model for the
generation of an eddy by such a mechanism. They established
that wavelengths of 50 km would have the highest growth
rates (which is similar to the observed diameter of the
eddy) but that such disturbances should travel slowly down-
stream. Such propagation has not yet been observed and the
repeated observations of the eddy in the same position led
Wadhams and Squire to speculate on the possiblity of a local
triggering mechanism - possibly the Molloy Deep, a 5770 m
depression located nearby at 79°10'N, 002°50'E.

Smith et al. (1984), in arguing that the principle of
conservation of vorticity could explain the generation of an
eddy in this region, developed a two layer model in a 2500 m
rectangular ocean basin centered on a 3500 m Gaussian shaped

120

depression and driven by a 0.1 m/s jet from the north-east.
The model generated a cyclonic eddy with a barotropic and
subsequently a baroclinic component. They suggest that their
results indicate that an eddy generated under the conditions
of their model should remain trapped in the vicinity of the
depression.

Over a 24 hour period on 24/25 August 1984, NORTHWIND
occupied a sequence of CTD stations from 79°N - 80°N adja-
cent to the Molloy Deep and through an ice edge feature
similar to that described above. The position of the
stations is shown in Fig. A.l. A narrow band (5 - 10 km) of
ice oriented generally east-west and comprised of densely
spaced small fragments of ice was observed in the vicinity
of Station 14. Ice concentrations at Stations 16 - 18 were
less than one tenth and an ice edge was encountered between
Stations 18 and 19 at which latter station a concentration
of six tenths was observed.

A temperature and salinity transect summarizing the
results of the CTD measurements made through this feature is
shown in Fig. A. 2. The location of the band of ice at
Station 14 is reflected in the sharply cooler near-surface
water which, as indicated by Bourke (1984), has a horizontal
gradient of temperature of 4°C in 5 km. The ice edge north
of Station 18 is marked by a surface layer of water less
than 0°C.

The center of the eddy is characterized by a layer of
>4°C water 100 m thick and 65 km in diameter near the
surface. Below 200 m, isohalines and isotherms at the center
are depressed at least 100 m deeper than their positions at
the apparent edges of the eddy. As Bourke (1984) points out,
such depression of the isotherms continues to at least
900 m, suggesting that the eddy exists to at least that
depth .

121

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80oN

79*N

Figure A.l The bathymetry and ice edge features in the
vicinity of Molloy Deep (after Smith et al. ,
1984). The position of the NORTHWIND 1984 CTD
Stations (underlined figures) is also shown.

123

400
I

40 50

DISTANCE

Figure A. 2

A temperature and salinity transect across the
Molloy Deep eddy feature. A band of brash ice
was located in the vicinity of Station 14 and
the ice margin was again encountered between
Stations 18 and 19.

124

Station Number

0.0

25.0

50.0

DISTANCE (KM)

75.0

99.2

Figure A. 3 The baroclinic velocity field relative to 1000
dbar near Molloy Deep. Westward flow is
indicated by positive isotachs.

125

LIST OF REFERENCES

Aagaard, K., and L.K. Coachman, The East Greenland Current
north of the Denmark Strait, I, Arctic, 2JL(3) , 181-200,
1968a

Aagaard, K., and L.K. Coachman, The East Greenland Current
north of the Denmark Strait, II, Arctic 21(4), 267-290,
1968b.

Aagaard, K., L.K. Coachman, and E. Carmack, On the halocline
of the Arctic Ocean, Deep-Sea Research, 28A(6) , 529-545,
1981.

Bourke, R.H., Preliminary results of the oceanographic
cruise of the USCGC Northwind to the Greenland Sea:
August - September, 1984, Tech. Rep. NPS 69-84-019,
Dept . of Oceanography, Naval Postgraduate School,
Monterey, Calif., 1984.

Fomin, L.M. , The Dynamic Method in Oceanography , Elsevier
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Helland-Hansen, B., The Sognefjord Section - oceanographic
observations in the northernmost part of the North Sea
and the southern part of the Norwegian Sea, James
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Liverpool, 1934.

Kiilerich, A.B., On the hydrography of the Greenland Sea,
Meddelser qm Gronland , 144(2), 6 3 pp., 1945.

Laktionov, V.A et al., Okeanograf icheskii ocherk severnoi
chast Grenlandskogo morya, Sovietskie Ribokh. Issled. y
Moryakh Evropeiskogo Severa, Moskva: Vniro-Pinro, 1960.

126

Mosby, H. , Water, salt, and heat balance of the North Polar
Sea and of the Norwegian Sea, Geofysiske Publikajoner ,
24, 289-313, 1962.

Newton, J.L., Hydrographic structure of the northeast
Greenland shelf; Fall 1979, in preparation.

Newton, J.L., and L.E. Piper, Oceanographic data from the
northwest Greenland Sea: Arctic East 1979 survey of the
USCGC Westwind, Rep. SAI-202-81-003- lj , Sci. Appl, Inc.,
San Diego, Calif., 1981.

Paquette, R.G., R.H. Bourke, J.L. Newton, and W.F. Perdue,
The East Greenland Polar Front in Autumn, J. Geophys .
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Perdue, W.F., Oceanographic investigation of the East
Greenland Polar Front, Master's Thesis, Naval
Postgraduate school, Monterey, California, 1982.

Perry, R.K., H.S. Flemming, N.Z. Cherkis , R.H. Feden, and
P.R. Vogt , Bathymetry of the Norwegian- Greenland and
w^J^tzyj}: Barents Seas , U.S. Naval Research Laboratory -
Acoustics Division, Environmental Sciences Group, William
and Heintz Map Corporation, Washington, D.C. 1980.

Reid, J.L., and A.W. Mantyla, The effect of the geostrophic
flow upon coastal sea elevations in the northern North
Pacific Ocean, J. Geophys. Res, 81(L8 ) , 3100-3110, 1976.

Riis - Carstensen , E., Fremsettelse av et dynamisk-
topographisk kort over Ostgronlandsstrommen Mellom 74° og
79° N.Br, paa grundlagaf hidtidige gjorte undersogelser i
disse egne, Geografisk Tidsskrift 41(1), 19 38.

Smith, D.C., J.H. Morison, J. A. Johannessen, and N.
Untersteiner , Topographic generation of an eddy at the

127

edge of the East Greenland Current, J. Geophys . Res . , 89
(C5), 8205-8208, 1984.

Swift, J.H., and K. Aagaard, Seasonal transitions and water
mass formation in the Iceland and Greenland Seas, Deep
Sea Res. , 28A (10), 1107-1129, 1981.

Tripp, R.B. and K. Kusunoki , Physical, chemical and current
data from Arlis II Eastern Arctic Ocean, Greenland Sea
and Denmark Strait area February 1964 - May 1965, Tech.
Rep. 185 Vols. 1 and 2, Ref. M07-29 Dept . of Oceanogr.,
Univ. Wash., Seattle, 1967.

Vinje, T.E. Landsat Rep. E77-10206, National Technical
Information Service, Springfield, 1977.

Vinje, T.E., On the use of data buoys in sea ice studies,
paper presented at WMO Workshop on Remote Sensing of Sea
Ice, World Meteorological Organization, Washington, D.C.,
Oct 16-20, 1978.

Wadhams , P'. , A.E. Gill, and P.F. Linden, Transect by subma-
rine of the East Greenland Polar Front, Deep Sea Res . , 26
(12A), 1311-1328, 1979.

Wadhams, p., Sea ice thickness distribution in Fram Strait,
Nature, 30J3 (3_930), 108-111, 1983.

Wadhams, P., and V.A. Squire, An ice-water vortex at the
edge of the East Greenland Current, J. Geophys . Res . , 88
(C5), 2770-2780, 1983.

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Ln? iqn

Thesis

T9343

c.l

218975

Tunniclif fe

An investigation of °f
the waters of the
East Greenland cur-

rent.
5 OCT

5 ;

8 0 4 5 1
~ ^ 5 1

Thesis

T9343

c.l

-"C375

Tunniclif fe

An investigation of
the waters of the
East Greenland cur-
rent .

feftrf