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oceanographic cruise to the bering and chukchi seas,
summer 1949

PART IV: PHYSICAL OCEANOGRAPHIC STUDIES: VOL. 1. DESCRIPTIVE REPORT

J. F.T. SAUR, PROPAGATION DIVISION
J.P. TULLY, PACIFIC OCEANOGRAPHIC GROUP, CANADA
E.C. LaFOND, PROPAGATION DIVISION

U.S. NAVY ELECTRONICS LABORATORY, SAN DIEGO, CALIFORNIA
A BUREAU OF SHIPS LABORATORY

This report covers work to January 1954 and was approved for publication 27 May
1954. The work was done under IO 15401, NE 120221-3 (NEL L4-1, formerly 2A5).

statement of problem

Investigate problems in oceanography through suitably devised methods, means, and
equipments. This report presents the results of physical oceanographic measurements
made in the shallow eastern Bering and Chukchi Seas.

conclusions

1. The oceanographic structure — temperature and salinity — of the region exhibits
pronounced layering with each layer nearly uniform vertically. The temperature-salinity
relations were consistent allowing a classification of the water masses, or layers, thus
making it possible to follow the geographical continuity of the water.

2. The annual development of the water masses can be accounted for by (a) the
cooling effect of winter conditions and the freezing of the ice, (b) melting of the ice in
spring and summer, (c) drainage and run-off from the continental areas, (d) modification
by heating, and (e) modification by mechanical mixing.

3. Water masses found in both the eastern Bering and Chukchi Seas are: (a) Deep
Shelf Water: uniform cold high-salinity water derived from winter conditions and lying
along the bottom in the deeper regions of the Bering and Chukchi Sea shelves, but not
present in the Bering Strait in late summer; (b) Modified Shelf Water: Deep Shelf Water
which has retained its high salinity, but since it is near the surface has been heated
several degrees; (c) Alaskan Coastal Water: warm water along the coast with greatly
varying salinities caused by fresh water drainage from the west coast of Alaska; and
(d) Intermediate Water: a wedge of water lying between, and probably formed by
mixing between, Modified Shelf Water and Alaskan Coastal Water.

Additional water masses observed in the Chukchi Sea are: (a) Siberian Coastal Water:
a counterpart to the Alaskan Coastal Water but lower in temperature, resulting from
drainage on the north coast of Siberia; (b) Ice Melt: low-salinity water at the surface in
the immediate vicinity of and in temperature equilibrium with the melting ice; and (c)
Modified Ice Melt: surface water fringing the Ice Melt and having similar salinities but
modified by heating.

4. Summer currents in the eastern Bering Sea move slowly northward, increasing in
speed at Bering Strait due to the geographical constriction. Superimposed on this slow
drift is a faster northward coastal current confined primarily to the Alaskan Coastal
Water. The Siberian Coastal Current, the Alaskan Coastal Current, and the westward
drift along the southern margin of the ice pack combine to establish a broad counter-
clockwise circulation in the Chukchi Sea.

recommendations

1. Obtain observational data at other seasons of the year to establish conclusively
the annual cycle of oceanographic structure and currents.

2. Undertake a limited study of the region between Cape Lisburne and Pt. Barrow to
tie together the Bering and Chukchi Sea investigations with those in the Arctic and
Beaufort Seas.

work summary

During the two-month cruise in the summer of 1949, systematic measurements were
made during a survey from the vicinity of St. Lawrence Island to Bering Strait, several
surveys in Bering Strait, two surveys northward from the Strait, and the return survey
from Bering Strait to Unimak Pass. The temperature, salinity, and density of the water
were established, and the distribution, movements, and interaction of the water masses
investigated.

The scientific group aboard HMCS CEDARWOOD was made up of J.P. Tully, A. J.
Dodimead, and R. H. Herlinveaux of the Pacific Oceanographic Group of Canada, and
E. C. LaFond, R. M. Lesser, J.C. Roque, and J.F.T. Saur, of the U.S. Navy Electronics
Laboratory. F.G. Barber and G.L. Pickard of University of British Columbia, though
primarily participating in the shore station program at Wales, assisted with observations
while on board.

preface

During the months of July and August, 1949, the U.S. Navy Electronics Laboratory
and the Canadian Pacific Oceanographic Group collaborated in a varied program of
acoustical and oceanographic research, mainly in the Bering and Chukchi Seas. This
joint venture was made possible through the cooperation of agencies of the Canadian
and United States Navies who furnished the vessels and necessary funds for the cruise.

Oceanographic measurements aboard the United States vessels were taken
primarily for the valuation of experimental sound-transmission and sound-propagation
data. The collection of sound data took priority, and oceanographic data could be
collected only when no interference with sound experiments was assured. The time of
the Canadian vessel was devoted exclusively to oceanography, and the data collected
by this ship are intended to supplement our present knowledge of the physical and
chemical characteristics of Arctic waters.

The expedition was made by three ships which formed a small task group under
the military command of Commander John D. Mason, USN. Dr. Waldo K. Lyon of the
Navy Electronics Laboratory directed the entire acoustic and oceanographic program,
with Dr. J. P. Tully of the Pacific Oceanographic Group as senior scientist in charge of
the Canadian Group.

Participating ships were:

USS BAYA (AG(SS) 318), under the command of CDR John D. Mason, USN;

HMCS CEDARWOOD, under the command of LCDR J. E. Wolfenden, RCN(R);

USS EPCE(R) 857,* under the command of LCDR D. J. McMillan, USN.

The oceanographic program was divided into three major parts:

1. Physical oceanographic studies. These were carried on primarily aboard
HMCS CEDARWOOD and from a shore station at Cape Prince of Wales. Some supple-
mental data were collected aboard USS EPCE(R) 857 and USS BAYA.

2. Oceanographic measurements as adjuncts to, and in support of, sonar work.
These measurements were taken from USS BAYA and USS EPCE(R) 857.

3. Sea floor and biological studies. This work was primarily conducted aboard
USS EPCE(R) 857, with some additional work on HMCS CEDARWOOD.

* Now designated USS PCER 857.

wi II WiHM NN

01 0072384 8

81

contents

INTRODUCTION

PREVIOUS INVESTIGATIONS
OBSERVATIONS
GEOGRAPHY

WATER STRUCTURE
General Character
Eastern Bering Sea
Bering Strait
Eastern Chukchi Sea

SURFACE CURRENTS
CONCLUSIONS
RECOMMENDATIONS ple

introduction

This report, the fourth of the series on the cruise, is concerned with the physical
oceanographic studies conducted in the shallow waters of the eastern Bering and
Chukchi Seas.* Results of the studies of the sea floor and currents, and oceanographic
investigations in the deep Bering Sea are covered in separate reports.':?:*

The dearth of oceanographic information in the Chukchi Sea and of coordinated
observations of the water structure to any distance on either side of the Bering Strait
has been brought out in previous reports. The program, therefore, was designed to
determine in more detail than had previously been accomplished the vertical and
horizontal temperature and salinity structure of the water in the approaches to Bering
Strait and especially in the Chukchi Sea region north of the Strait. The temperature,
salinity, and density of the water were to be established, and the distribution, move-
ments, and interaction of the water masses were to be investigated.

The objectives were obtained by a survey from the vicinity of St. Lawrence Island
to Bering Strait, several surveys in Bering Strait, two surveys northward from the Strait,
and the return survey from Bering Strait to Unimak Pass. Because of time and operational
considerations, the ice was reached on only one occasion for a period of 8 hours so
that the coverage north of 70°N latitude, especially in the region near the ice, was
not as complete as desired. The operation provided good data in the areas covered
and valuable experience on oceanographic operations in the Arctic regions.

previous investigations

The complicated physical oceanography of the Bering and Chukchi Seas has
been investigated by various organizations. The Norwegian ship Maud obtained con-
siderable oceanographic data in the western Chukchi Sea between Herald Shoal and
Wrangel Island, but occupied only two serial stations east of 170° W.*

Other principal pre-World War Il investigations were carried out by University
of Washington oceanographers in the summers of 1934, 1937, and 1938 aboard U.S.
Coast Guard vessels.®° On these cruises, comprehensive chemical and physical oceano-
graphic data were obtained at serial stations giving wide coverage in the eastern
Bering Sea and Bering Strait, and on one occasion data were obtained along the
Alaskan Coast nearly to Pt. Barrow. Recent translations of Russian documents’ furnish

*Volume 2 of this report contains the observational data.

1£.C. Buffington, et al. Oceanographic Cruise to the Bering and Chukchi Seas, Summer 1949,
Part I: Sea Floor Studies (Navy Electronics Laboratory, Report 204) 2 October 1950.

2R.M. Lesser and G.L. Pickard Oceanographic Cruise to the Bering and Chukchi Seas, Summer
1949, Part Il: Currents (Navy Electronics Laboratory, Report 211) 24 October 1950 (CONFIDENTIAL)

3 J.F.T. Saur, ef al. Oceanographic Cruise to the Bering and Chukchi Seas, Summer 1949,
Part Ill: Physical Observations and Sound Velocity in the Deep Bering Sea (Navy Electronics Laboratory,
Report 298) 6 June 1952 (CONFIDENTIAL)

4H.U. Sverdrup “The Waters on the North-Siberian Shelf” (In: The Norwegian North Polar
Expedition with the ‘Maud, 1918-1925 Scientific Results) J. Griegs, vol. 4, no. 2, 1929, pp. 34-40.

5 €. A. Barnes and T. G. Thompson Physical and Chemical Investigations in Bering Sea and Portions
of the North Pacific Ocean University of Washington, 1938. E

6 J.R. Goodman, ef al. Physical and Chemical Investigations: Bering Sea, Bering Strait, Chukchi
Sea, during the Summers of 1937 and 1938 University of Washington, 1942.

7G.E. Ratmanoff Explorations of the Seas of Russia (Hydrological Institute. Leningrad, Publication
no. 25) 1937, pp. 1-175.

additional chemical and physical data on the western Bering Sea and Bering Strait,
and some data are given in a Japanese publication® concerned primarily with the
oceanography along the Asiatic Coast.

During World War Il, the U.S. Navy collected large numbers of bathythermo-
grams in the southern Bering Sea. These data provide detailed temperature structures
of the upper layers,? but no concurrent salinity data are available.

Post-war investigations consist of bathythermograph sections and a few serial
stations obtained in 1946, 1948,1° and 19501! from icebreakers on runs through the
Bering and Chukchi Seas to Point Barrow. These observations were made by personnel
of the U.S. Coast Guard, U.S. Hydrographic Office, University of Washington, and
Scripps Institution of Oceanography. The Fish and Wildlife Service obtained surface and
bottom temperature data in eastern Bering Sea in June and July 1949,’? the same year
as the cruise reported here. In the summer of 1947 complete oceanographic stations
were occupied through the Bering and Chukchi Seas to a latitude of 72°N by personnel
from the Navy Electronics Laboratory and the Scripps Institution of Oceanography
aboard the USS NEREUS.!® The majority of these data were taken in the central and
eastern Chukchi Sea and comprise the major work in this region north of Bering Strait
previous to the presently reported cruise.

observations

HMCS CEDARWOOD occupied 192 serial stations, the locations of which are
shown in figure 1. During the first part of the cruise, in the southern area, a bathy-
thermograph and a C-T-D (conductivity-temperature-depth) instrument were used at
each station and a Nansen-bottle cast was made at about every fifth station. The use
of the C-T-D, which recorded the three variables simultaneously as the element was
lowered into the water, was discontinued because too great inaccuracies in conductivity
were caused by the slow rate of flushing of the cell. Reversing thermometers were
removed from the water sampling bottles after station 44 for two reasons, (1) a delay
in time was required for the thermometers to reach equilibrium, and (2) because of
the magnitude of short-period fluctuations and the ranges encountered, an accuracy of
better than -0.2°F (which could be obtained with a bathythermograph) was not
considered necessary.

8K. Hidaka Oceanographic Investigations in the West Pacific Ocean, Part I: The Northern Area
of the West Pacific Ocean, No. 1. Investigations from the Standpoint of Marine Physics (Eastern Asia
Research Institute) 1952.

9J.G. Pattullo, et al. Sea Temperature in the Aleutian Island Area (Scripps Institution of
Oceanography, Oceanographic Report no. 24) April 1950.

10 €.W. Thomas Physical and Zoological Investigations in Bering Sea and Portions of the Arctic
Ocean (Coast Guard) 1948 (CONFIDENTIAL).

11U.S.S. BURTON ISLAND (AGB-1) Beaufort Sea Oceanographic Expedition, Summer 1950
August 1950 (CONFIDENTIAL).

12 J. G. Ellson, et al. Exploratory Fishing Expedition to the Northern Bering Sea in June and July,
1949 (Fish and Wildlife Service, Fishery Leaflet no. 369) March 1950.

13 £.C. LaFond, et al. Oceanographic Measurements from the USS NEREUS on a Cruise to the
Bering and Chukchi Seas, 1947; interim report (Navy Electronics Laboratory, Report 91) 25 February 1949.

167° 30!

@ OCEANOGRAPHIC STATION
© BT's ONLY

Figure 1. Location of stations, summer 1949: (a) eastern Bering
and eastern Chukchi Seas; (b) Bering Strait.

Thereafter, a standard procedure was adopted for all stations. When the ship
had stopped, a bathythermograph was first lowered to the bottom. The slide thus
obtained was placed with its grid in a photographic enlarger and projected to show
the thermal structure. From this trace, the depths of water sampling were selected. They
usually included at least the surface, a depth just above the thermocline, one below the
thermocline, and one near the bottom. The number of samples taken depended upon
the complexity of the thermal structure and the depth to the bottom, but usually ranged
from five to seven.

Nansen bottles without attached thermometers were placed appropriately on
the line to take water samples at the selected depths. A record of the temperature was
obtained from the bathythermograph secured to the end of the same line. The complete
operation took about 15 minutes and was repeated about every two hours if the ship
remained at the same location.

A single 180-foot-maximum-depth (Bristol 20120) bathythermograph was used
for 554 lowerings and a 450-foot instrument was used for 27 lowerings in the area of
the southeastern Bering Sea. Additional observations (such as plankton-net hauls,
bottom samples, surface-current and bottom-current measurements) were made at
selected stations and have been reported separately.'1*

Salinity analyses and preliminary analysis of bathythermograms were performed
aboard ship for several reasons. They made it possible to evaluate and modify the
over-all program in the field, to determine and obtain the most pertinent information
in the time available, to determine the proper operation of gear, and to avoid accumula-
tion of water samples.

The BT slides were placed in a grid, adjusted for preliminary temperature
corrections, and projected and traced on mimeographed grid prints which had been
prepared in advance. The water samples were titrated on shipboard and the salinity
calculated to an accuracy of +0.05°/o9. The salinity was then plotted on the grid
with the temperature trace. Density values (o;) were calculated by means of a nomogram
and also plotted on the grid. From these vertical traces preliminary geographic sections
of temperature, salinity, and density were prepared. This procedure of shipboard
preliminary processing proved to be highly satisfactory.

Detailed processing and analysis were carried out ashore. The serial data are
tabulated and horizontal and vertical sections of temperature, salinity, and density
distributions are given in volume 2 of this report.

geography

The eastern Bering and Chukchi Seas lie on the broad continental shelf of Alaska.
The continental shelf is remarkably flat, varies in depth primarily between 20 and 30
fathoms, and has a mud and sand bottom shoaling gradually and regularly toward
the coastline. Detailed descriptions of the topography and sediments of the region are
given in the first report of this series! and a report of the NEREUS cruise in 1947.

The shallow coastal seawater system is bounded on the southwest and south by
the deep Bering Sea and the Aleutian Islands, on the east by the coast of Alaska, on
the west by Siberia, and on the north by the Arctic Ocean. The system is divided into
two distinct regions by the Bering Strait which separates the Bering Sea from the Chukchi
Sea. Oceanic water is supplied to the southern part of the system by the flow northward
through the eastern Aleutian Islands and perhaps also by a weak northeastward flow

14 Navy Electronics Laboratory, Report 148 Oceanographic Cruise to the Bering and Chukchi
Seas, Summer 1949; Interim Summary Report 19 October 1949 (CONFIDENTIAL).

across the deep Bering Sea.?:® Fresh water is contributed to the eastern Bering Sea by
two large Alaskan rivers, the Kuskokwin and the Yukon. A third large river, the Anadyr
in Siberia, also empties into the general region but its effects are felt southwestward
along the Siberian coast. In the Chukchi Sea region three rivers flowing into Kotzebue
Sound also contribute a large amount of fresh water. Additional details of the geography
are brought out in the excellent descriptions of the area by Barnes and Thompson? and
by Goodman, Lincoln, Thompson, and Zeusler.®

water structure
GENERAL CHARACTER

Vertical distributions of temperature and salinity in nearly the whole region
exhibited a pronounced layering effect typicel of coastal systems involving large
quantities of run-off. Relatively sharp boundaries separated these layers which in them-
selves could be considered virtually uniform with depth (fig. 2). Frequently in horizontal
distributions, distinct boundaries also separate water of different characteristics. These
geographic distributions will be discussed after first establishing the characteristics of
the water masses in the region.

The temperature-salinity (T-S) relation (correlation of temperature with salinity)
was investigated to determine if it could be used to identify the water masses of the
region. This procedure has been used frequently in oceanic studies to classify and identify
water masses and to trace their movement. It has been used less frequently in coastal
or shallow water studies because of the effect of changes at the atmospheric and the
coastal boundaries. The temperature and corresponding salinity of each water sample
is plotted on a graph using temperature as the ordinate and salinity as the abscissa, as
shown for selected stations in figure 8.* These points with the depth indicated are joined
by a smooth curve. If the relation is consistent between various stations in shape and
location on the diagram, the curve for any individual station can then be used to identify
the water mass or masses present.

The T-S relations in the Bering and Chukchi Seas were consistent. Such consistency
in this shallow-water region was maintained because the surface boundary effect was
minimized by a constant stratus overcast and high relative humidity during this time of
year. At any given staticn, except those close to the coast, the points for depths above
the thermocline were closely grouped, as were those for depths below the thermocline
(fig. 8). A wider scatter of points occurs as a result of geographic variation when the
points for all the stations are plotted (fig. 2a). Nevertheless, a general grouping of
points occurs so that water masses can be identified and the geographic continuity of a
given water mass can be followed.

The water masses used here should not be confused with the deep-sea water-
mass classifications of Helland-Hansen!® and Sverdrup.!° The water masses defined
here are purely local and apply only to the shallow Bering and Chukchi Seas and are
used as tools to trace the continuity and development of the system. Certain of these
masses may be only transient and not even in existence throughout the whole year.
They also may vary somewhat from year to year, but the general structure of the system
as indicated by these water masses appears consistent with previous data.°»°:".")18

* Figures 8 through 13 appear as foldouts at the end of the report.

15 B. Helland-Hansen “Nogen Hydrografiske Metoder’ Skandinaviske Naturforsker Mote 1916.

16 H.U. Sverdrup, et al. The Oceans, Their Physics, Chemistry, and General Biology Prentice-
Hall, 1942.

TEMPERATURE (°F)

TEMPERATURE (°F)

8
22.5

Figure 2a. Frequenc
60, 80, 100, 125, 150 feet. Figures

24.0

y of T-S relationships in

Sete (°/00)

show number of observations in

Figure

2b. T-S relationships us

26.0 28.0

SALINITY (°/o0)

ed to designate water masses

of the ea

30.0

stern

it
Hi
nn I
a a
Hh

»
THA
dnt

Il i

an

<y =

the Chukchi Sea from interpolated depths of 0, 20, 40,

unit of diagram 1°F by 0.25 9/0, salinity.

33.5

DEEP SHELF WATER

32.0

Bering and Chukchi Seas.

33:9

Figure 2a shows the frequency scatter diagram for the samples at given depths
at all of the stations occupied in the Chukchi Sea. In the upper part of the diagram, a
relationship exists in which the salinity changes over a wide range from around 20 97/00
to 30°/o9 while the temperature varies only between 50° and 46°F. This grouping of
points identifies the surface water near the coast of Alaska and will be called Alaskan
Coastal Water (ACW) (fig. 2b).

Around 45°F and 30.5 °/o9, the slope of the relationship changes and remains
constant to about 40°F and 32.0°/o 9. Observed values which cluster about the line
joining these points are characteristic of a second water mass designated as Intermediate
Water (IW). A further grouping occurs in the region approximately bounded by 34°
to 40°F and 32.00 to 33.00 °/o9. This relationship is typical of the water lying on the
bottom throughout most of the area during late summer and will be labeled Modified
Shelf Water (MSW). The water mass defined by the group of observed values around
30°F and between 31.50 and 33.00 °/o9 will be designated as Deep Shelf Water (DSW).
The above four water masses include the majority of the observations and are applicable
also to the T-S relation found in the northern part of the eastern Bering Sea. Southward
from St. Matthew and Nunivak Islands the slightly higher salinities, about 31.0 to
32.0 °/o9, obtained in the warm surface water, 46° to 50°F, were due to the influence
of surface water from the Pacific filtering through the passes of the eastern Aleutian
Islands.

In the Chukchi Sea three additional water masses are present. Fewer points for
these masses are shown in figure 2a as each covered only a small geographic area
and was thus sampled less often. One of them exhibits a wide range of low salinity,
26 to 29.5 /o, similar to the Alaskan Coastal Water but with lower temperatures, 38°
to 43°F. This is Siberian Coastal Water (SCW) originating north of Bering Strait. Siberian
Coastal Water from south of Bering Strait was not encountered. The water mass having
a temperature of near 30°F and salinity between 28.75 and 30.50°/ 9 is found only
in the region of the melting ice and is called Ice Melt (IM). The last water mass
occurs in the diagram (fig. 2a) around 38°F and 30°/ oo. It is a surface water mass
separating the Ice Melt and the Intermediate Water and will be designated Modified
Ice Melt (MIM).

The above designations are made for convenience in the following discussion
of the distribution of the water masses in the eastern Bering Sea, Bering Strait, and
eastern Chukchi Sea.

EASTERN BERING SEA

Temperature and salinity distributions at the surface in the eastern Bering Sea
from the present data are shown in figure 3. These should be considered as “smoothed”
representations for the period of the survey, as definite fluctuations and development
of the distributions with time were observed, particularly just to the north of St. Lawrence
Island. In figure 4, similar representations are shown for a depth of 80 feet (approxi-
mately 25 meters). The close relation between the temperature and salinity distributions
in the eastern Bering Sea is very striking. In general, warm low-salinity water lies close
to the coast grading to cold high-salinity water at a distance from the coastline, both at
the surface and at depths. Alaskan Coastal Water lies close to the shore and has the
highest temperatures and lowest salinities observed in this region. The Modified Shelf
Water appears farther from the coast and just northward from St. Lawrence Island as
an area of cold high-salinity water widening to the northwest. Due to the time differences
and spacing of the lines of observation, the data could be interpreted in two ways, that
shown in figures 3 and 4 is believed representative of conditions in July and early

°
ae ag

As Ss
ive

NA

SERREPS”
cee Me a
P2ESRRBBE
(ae eae

or
GRADS 322 naa

ese BARES AREAUAY
TOSS ee
EUBG Eman “MELLEL EER

Figure 3. Distributions of (a) surface temperature (°F) and (b) surface salinity (0/9) in the eastern
Bering Sea.

eh iG
a Be haa

oe

gh ee :
a ee Oe eee et ae ane

Figure 4. Distributions of (a) temperature (°F) and (b) salinity (970) at 80 feet in the eastern Bering Sea.

12

August. The other interpretation would be representative of mid-August when the flow
of warmer water around the west tip of St. Lawrence Island and westward: from the
north side of Norton Sound leaves an isolated cold spot to the north of the east tip
of St. Lawrence Island. This situation is shown in the analysis by Hidaka® and the
late-summer data of University of Washington,”*® and can be seen occurring at the
80-foot level in our data. Further observations in this region are required to determine
the details of the development.

The Intermediate Water separates the Alaskan Coastal Water and the Modified
Shelf Water. The Intermediate Water appears to originate in the region of Nunivak
Island and Cape Romanzof where the water is almost homogeneous from top to bottom.
The mechanism which brings about the pronounced uniformity is not definitely known
at the present. To the north of this region the Intermediate Water is maintained as a
transitional zone between the Alaskan Coastal Water and the Modified Shelf Water.
It nevertheless exhibits boundaries in the vertical profile with the other water masses.

A schematic presentation of the water masses along a section from Wales south-
westward through the Strait of Anadyr, and the vertical distributions and the T-S
relationship at several stations along the section are shown in figure 9 (foldout). The
separation of the shaded water-mass types in the schematic diagram represents the
boundary between the water masses. In most cases this change is abrupt, but in some
cases the change takes place over a fairly broad region of transition as indicated by the
wider separation.

The Alaskan Coastal Water is confined to a narrow region very near the coast.
The Modified Shelf Water lies along the bottom over most of the section and appears
at the surface in the center of the section near the Siberian Coast. At the surface, a
moderate sized area of Intermediate Water exists between the Alaskan Coastal Water
and the Modified Shelf Water, but at depths the Modified Shelf Water intrudes close
to the coast. Intermediate Water passing around the western end of St. Lawrence Island
is found near the surface near the southwestern end of the section.

Deep Shelf Water is found on the bottom intruding from the southwest into the
Strait of Anadyr west of St. Lawrence Island. This water has approximately the same
salinity as the Modified Shelf Water but is colder and is separated from it by a marked
thermal boundary. The Deep Shelf Water is found also at stations 32 through 34 on
the south side of St. Lawrence Island. It is a persistent type and was found in this region
in both investigations conducted by the University of Washington (see NORTHLAND
station N-363, fig. 9). Both past and present data indicate that the Deep Shelf Water
intrudes from the southwest into the Strait of Anadyr, but during late summer does not
extend to the Bering Strait. Thus it appears that although there may be northward
movement of water along the bottom in this region, it is so slow that it is warmed
several degrees as it rises into the shoaler area north of St. Lawrence Island. In fact,
data from earlier sources indicate that this temperature boundary between Deep Shelf
Water and Modified Shelf Water recedes southward from the region of Bering Strait
as the summer season progresses.

The whole system of water increases in density with distance from the Alaskan
Coast, except where the surface flow is interrupted by the barrier created by St.
Lawrence Island. From the density distribution and from the direct current observations
made in Bering Strait,*:° it appears that the water masses are flowing slowly north-
ward throughout the area, converging toward Bering Strait with a rapid flow being
concentrated near the coast in the Alaskan Coastal Water and at the boundary between
it and the Intermediate Water.

BERING STRAIT

Bering Strait, some 47 miles in width at its narrowest portion and averaging
about 27 fathoms in depth, is the only connection between the waters of the Bering
Sea and the Chukchi Sea. A schematic section showing the water masses flowing
through the east side of Bering Strait is given in figure 10 (foldout).

Three water masses are found passing through Bering Strait: Alaskan Coastal
Water, Intermediate Water, and Modified Shelf Water. The boundaries’ between the
water masses are very sharp, in fact, they. are often visible as marked convergence
lines at the surface. The geographical position of the convergences exhibited a tendency
to shift about a mean position, probably because of changes in wind conditions and
variations in the fresh water supply. Secondary convergence lines indicated cellular
circulation with the axes parallel to the direction of the currents within the Alaskan
Coastal Water.

The Alaskan Coastal Water extends westward on the surface for about 4 to 8
miles from the Cape Prince of Wales. Modified Shelf Water occurs from the surface
to the bottom near Little Diomede Island, and, according to University of Washington
data, this same phenomenon occurs throughout the western half of the Strait (see
NORTHLAND station N-333, fig. 10). On the Alaskan side, the Alaskan Coastal Water
intrudes along the bottom close to the coast beneath the Intermediate Water, which
occurs only as a narrow separating wedge. Thus, the Deep Shelf Water of the Bering
Sea shows no continuity through the Strait. The other three water masses found in the
southern approaches, Alaskan Coastal Water, Intermediate Water, and Modified Shelf
Water, are continuous through the Strait into the Chukchi Sea. The flow is to the north
through the entire width of the Strait, and a concentrated flow exists near the boundary
between the Alaskan Coastal Water and Intermediate Water on the eastern side.

In the observations in the published data (limited to summer conditions), on one
occasion, in 1933,’ the current was observed to flow south in Bering Strait. This occurred
only very near Cape Deshneva on the Siberian Coast, with a speed of about 30
centimeters per second at the surface and at 15 meters depth, decreasing to about
10 centimeters per second at the bottom. This flow, however, did not continue southward
along the coast but was swept northward again by the dominant north-flowing currents.'“
Although this south-flowing current is of slightly lower salinity than the Modified Shelf
Water, there. is no reason to believe that the over-all water-mass distribution is ma-
terially affected by limited and sporadic reversals of current on the extreme western
side of the Strait.

EASTERN CHUKCHI SEA

Distributions of temperature and salinity in the eastern Chukchi Sea for the surface
are shown in figure 5, and for 80 feet (approximately 25 meters) in figure 6. Again
the presentations for the surface show an average condition for the two series of
observations made about two weeks apart during August. A definite increase in the

17 Chelyuskin Expedition, 1933-1934 The Voyage of the Chelyuskin, by Members of the Expedition
Macmillan, 1935. Professor Otto J. Schmidt writes in this narrative report: ‘“After making a number of
loops [near Cape Serdzekamen] the Chelyuskin took a southeasterly direction and on November 3 we
entered Bering Strait. We entered the drifting ice-pack together, but not under our own power. All the
same, in one voyage there we were, arrived at Bering Strait. On November 5 we were already half-way
through, near St. Diomede Island. . . . Though the distance to clear water was not great (about 20
kilometers), the ice was extremely solid ....

“. . Then suddenly our ice-pack began a rapid northerly drift. It was clear that we were in

the course of a powerful current from the Pacific into the Arctic Ocean towards Herald Island . . ..”

13

ne Bee

Figure 5. Distributions of (a) surface temperature (°F) and (b) surface salinity (9/00) in the eastern
Chukchi Sea.

14

Ki MW
AN
\

GHUKCH! SEA
i ' Wa Ne \
a
ANWAR
\ AN
NAN
AN

i \\
a
WY
BERING SEA \ u any BERING SEA t
a
a \ \ 4 {-
i y

eA 165° 760°

Figure 6. Distributions of (a) temperature (°F) and (b) salinity (9/9) at 80 feet in the eastern Chukchi
Sea. ‘ :

15

16

amount of low-salinity water along the coast, especially north of Pt. Hope, was observed
between the two series. Little change was observed at the 80-foot level except a
slight salinity decrease very near the coast.

In the Kotzebue Sound region the warmer low-salinity Alaskan Coastal Water can
easily be followed flowing around the Sound parallel to and near the coastline. However,
as the distance from the shore is increased the temperature and salinity patterns dis-
sociate, a phenomenon not observed in the shallow Bering Sea. The surface temperature
west from Kotzebue Sound decreases continuously to the westward while the salinity
increases until it reaches a maximum of about 31.50°/ 9 and then decreases sharply
to less than 30.00 °/o0. The latter salinity occurs directly north of the Bering Strait
and is caused by the cold Siberian Coastal Water which flows southeastward along
the Siberian Coast but is turned northward near East Cape by the strong flow through
the Strait. This turning point must fluctuate with the strength of the flow along the
Siberian Coast and would account for the rare observations of a southerly current
at Cape Deshneva. At the 80-foot level, both the horizontal temperature and salinity
gradients are more pronounced than at the surface. The salinity distribution, in par-
ticular, shows that the shelf waters persist over the greater part of the shelf at the
bottom even in late summer. Thus, large seasonal variations occur only very near
the coast and in the surface waters.

Figure 11 (foldout) presents schematically the distribution of the water masses
along a section extending from Shishmaref Inlet (C) to the northwest into the central
part of Kotzebue Sound (C’) and back northeastward to Pt. Hope (C”). Alaskan
Coastal Water extends at the surface some 40 miles seaward near Shishmaref Inlet.
A large region of Intermediate Water is associated with the maximum salinity in
the surface distribution, and the Siberian Coastal Water intrudes as a shallow layer
in the western apex of the section. Modified Shelf Water occupies most of the deeper
region.

The second part of the section (C’ to C”) northeastward to Pt. Hope shows
that the Alaskan Coastal Water is concentrated within less than 10 miles of the coast
and the zone of the Intermediate Water tends to be narrower than in the first part.
Both the Siberian Coastal Water and the Modified Shelf Water water masses intrude
much closer to Pt. Hope than to Shishmaref Inlet. It will be recalled that a similar tendency
for the Intermediate Water zone to become narrow on the south side of a point of
land was observed in the section running southwestward from Cape Prince of Wales
(fig. 9).

Figure 12 (foldout) presents schematically the distribution of the water masses
along a section northwestward from near Cape Lisburne. The Alaskan Coastal Water
occupies an extensive region at the surface. The Intermediate Water is associated
with a weak salinity maximum at the surface and beneath it lies Modified Shelf Water.
At the seaward limit of the section Modified Ice Melt appears as a shallow surface layer.
This location suggests that the boundary of the ice lies southwestward from station 90,
although the boundary of the ice may have moved south in the two weeks since the
ice was actually reached at station 90.

Figure 13 (foldout) shows the distribution of the water masses from Cape
Lisburne northward to 73° N where the ice pack was encountered on this survey. The
sections in this figure were taken following a period of high southerly winds, Beaufort
force 5 to 7, and while the winds still remained at about force 4. The drift ice had
moved northward with the wind and very little ice was encountered prior to reaching
the definite boundary of closely packed drift ice into which the wooden-hulled vessel
could not penetrate.

The same water masses exist along this section as along the previous one, but
to a greater extent. Intermediate Water at the surface is associated with the center
of high salinity (31.50 °/o9) and a tendency for cyclonic circulation. At this distance
from the coast there has occurred less mixing with Alaskan Coastal Water so that
the central part of this Intermediate Water region still contains a high percentage of
the Modified Shelf Water.

A water mass having the same characteristics as, but not geographically con-
nected with, the Deep Shelf Water of the Bering Sea appears along the bottom at
the seaward end of the section. The nomenclature is retained because we believe that
the two masses have the same general origin (see discussion in Conclusions).

In the region of the drifting ice along the periphery of the ice pack is cold
low-salinity Ice Melt. This water has the same salinity characteristics as the previously
defined Modified Ice Melt (fig. 2) and thus is differentiated from it only by temperature,
indicating that it warms rapidly as soon as it is isolated from the melting ice pack.
On the other hand, the Ice Melt water has the same temperature characteristic as the
Deep Shelf Water and is differentiated from that mass only by salinity.

In summary, the three water masses, Alaskan Coastal} Intermediate, and Modified
Shelf Waters, are continuous from the Bering Sea through the Chukchi Sea. Deep Shelf
Water occurs in both seas but has no continuity through the Strait at this season. The
Siberian Coastal Water, Modified Ice Melt, and Ice Melt are found in the Chukchi but
not in the eastern Bering Sea.

surface currents

Movements of the water masses are generally determined by dynamic compu-
tations, by direct current observations, or qualitatively by the temperature and salinity
distributions.

The dynamic topography of the surface, computed over a selected reference
level, indicates the speed and direction of the current at the surface relative to that
of the reference level.1® The relative current was computed over a reference level of
130 feet to determine if this method would agree with the few observed current measure-
ments and thus give a valid picture of the surface-current pattern throughout the area.
In most instances, except in Bering Strait where the relative current was large, the
computed current was only a small fraction of that observed. It was evident that the
movement at the reference level was usually much greater than the relative current
computed between the 130-foot level and the surface.

Another means of determining the speed of the current is by the geographic
displacement of water of a given type during a limited time. This method was used
to determine the speed of the coastal current from Kotzebue Sound around Pt. Hope.
Low-salinity water of less than 29°/o9 was found at station 67 on 10 August 1949,
0405Z, but did not appear northward along the coast. Similar low-salinity water was
found at station 149 on 22 August 1949, 1735Z. These measurements imply a progress
of about 200 miles (a minimum value because of the mixing) along the coast in 1242
days, an average speed of between 0.5 and 0.9 knot depending on the course traveled.

18 J. W. Sandstrom and B. Helland-Hansen ‘Uber die Berechung von Meeresstromungen” Nor-
wegian Fishery and Marine Investigations, vol. 2, no. 4, 1903.

17

18

The general pattern of the surface currents can be inferred from the distribution
of the water masses taken together with the dynamic topography and direct current
measurements. The currents obtained in this manner are shown in figure 7 for the north-
eastern Bering Sea and eastern Chukchi Sea during the late summer of 1949.

The flow is predominantly northward from the region between St. Matthew and
St. Lawrence Islands to as far north as 70° N. The flow of the Alaskan Coastal Water
close to the coast is very pronounced. In the Bering Sea, the current passing around the
east end of St. Lawrence Island and north to Bering Strait is somewhat strengthened
by outflow from Norton Sound and the Yukon River. The major current through Bering
Strait appears in the eastern half of the strait.

In the Chukchi Sea, in addition to the coastal current a moderate flow entering
from the southwest appears along the northern side of the tongue of Siberian Coastal
Water. This flow probably contributes to the split in current occurring west of Pt. Hope
and Cape Lisburne. In this region one branch of the split current appears to proceed
northwest toward Herald Shoal and the other follows northeast along the Alaskan
Coast. North of 70°N, the predominant feature in the area surveyed is the eddy
between the coastal current and the Arctic drift with an indication of a weak south-
westward return of lower-salinity surface water in the northwestern part of the area.

conclusions

In the preceding sections the identification, distribution, and movements of the
water masses have been discussed with only slight reference made to their origin.
From the present available data, an hypothesis of development of the system is pro-
posed for consideration and further investigation.

During the winter months the ice boundary progresses southward, not by current
drift or wind effect but because of the atmospheric cooling. Because of the high winds,
lack of run-off, and the freezing of the ice, a vertically uniform water mass probably
exists in late winter from the Chukchi Sea through Bering Strait and over the greater
part of the shallow Bering Sea. This water mass is then in equilibrium with the freezing
ice, which for water of salinity of 33:00 °/oo is a temperature of 28.8° F.* This is the
origin of the Deep Shelf Water. /

As the ice recedes in the spring, the winds continue mixing so that Ice Melt water
is dissipated except at the immediate ice boundary. However, the effects of surface
heating and solar radiation as spring progresses warm the surface layers of the water
mass, developing the Modified Shelf Water.

At the same time the warmer coastal drainage progressively creates the Alaskan
Coastal Water near shore. The outflow from several rivers renews the water mass
downstream so that the identity or characteristics are maintained at least as far north-
ward along the Alaskan Coast as Cape Lisburne. The stations northeast of Cape
Lisburne indicated some deterioration of the Alaskan Coastal Water.

The Intermediate Water appears to be largely a broad zone of mixing which
develops between the Modified Shelf Water and the Coastal Water. It first occurs
south of St. Lawrence Island off Cape Romanzof where it extends over a wide area,

* An expedition aboard the USS BURTON ISLAND (AGB-1) in February 1951 observed vertically
uniform conditions in the region of the ice in the northeastern Bering Sea northward to the latitude of
64° 50’. Observed temperature was 28.9°F and salinity ranged from 31.89/ 9 to 33.49/99 depending
upon location.

homogeneous from top to bottom. It may have its
origin in mechanical mixing over the bottom rise in
that area. It further appears to be renewed by
mixing between Alaskan Coastal Water and Modi-
fied Shelf Water.

In the Chukchi Sea region it would be antici-
pated that the run-off of the rivers along the north
Siberian coast would create a coastal current moving
southward along the western side of Bering Strait
as a counterpart to the northward flow of Alaskan
Coastal Water. Such a current was not found in the
Bering Strait, nor was it indicated by the observa-
tions of USCGC CHELAN in 1934° or the NORTH-
LAND in 1937 or 1938.° Thus, it appears that the
low-salinity cool water found directly north of Bering
Strait to the west of Kotzebue Sound is the Siberian
coastal current which has been diverted by the
strong flow through Bering Strait and is carried
northeastward away from the coast. This mass of
Siberian Coastal Water, which moves out of the
surveyed area, with time and displacement would
tend to lose its identity because of mixing. The Modi-
fied Ice Melt water also moves west and southwest
out of the area surveyed. It is possible that some of
this water moves southward in the region of Wrangel
Island and combines with the flow of Siberian
Coastal Water to set up a weak cyclonic gyral
between Wrangel Island, the Siberian Coast, and
the region near Herald Shoal.

The shallow Bering and Chukchi Seas thus form
a coastal system with a general structure which is
consistent from year to year. The water masses are
derived from four distinct sources, Alaskan coastal
drainage, Siberian coastal drainage, freezing of
the ice in winter, and melting of the ice in summer.
The other water masses are modifications of these,
two arising from heating effects and the third from
a mixing between water masses.

Figure 7. Surface currents in the eastern Bering Sea and the
eastern Chukchi Sea. Surface current arrows indicate only ap-
proximate strength and persistency of current.

7\ }
fi Molitegte li 7i Zab
cl | A j
| y,

2
|HERALD SHOAL 4

* i EAT ev yay
itt, Auta eA

y N
EARN Nee
Fi

rt 4!
eS Gn ete

20

recommendations

Our knowledge of the American waters of the Bering Sea, Chukchi Sea, and
Arctic regions has been increasing at a relatively rapid pace since 1947. Subsequent
to the presently reported cruise, unpublished oceanographic surveys have been carried
out in the navigable regions of the Beaufort Sea in conjunction with BAREX Operations
of 1950, 1951 and 1952. SKIJUMP Operations!®:*° have furnished spot data on oceano-
graphic conditions under the icepack, and a major effort is being applied in extending
the boundaries of the surveyed areas. There still remain, however, several problems
in the Bering and Chukchi Sea regions for which more data would be desirable.

Observational data are needed in these areas at other seasons of the year
to supplement the summer data and the sparse amount of winter data. Such information,
including year-around current measurements at Bering Strait, would assist in answering
the long-standing question of the driving force behind the persistent northerly flow
through Bering Strait in summer. Although it has been generally assumed that there
is a difference in level between the Pacific and Arctic Oceans® which results in the
northerly current year around, this theory has not been satisfactorily substantiated.
It is possible, however, that a change in level may take place locally within the Bering
and Chukchi Seas due primarily to the difference between wind stress exerted in the
summer and in the winter, and secondarily to the run-off of fresh water from the western
Alaskan Coast during the summer months. (Unpublished data at NEL on currents in the
eastern side of the Bering Strait indicate that even in summer months the current through
the Strait can be reversed by several days of strong northerly winds.)

The mechanism which results in the large area of nearly homogeneous water
in the Nunivak Island, St. Matthew Island, Cape Romanzof area is still unknown, as are
the relative amounts of water supplied to the region by flow from the southwest across
the deep Bering Sea and by flow from the south through the eastern Aleutian passes.

Present data on the circulation around St. Lawrence Island which forms a
partial block to Bering Strait are somewhat contradictory, particularly regarding struc-
ture to the north of the island. The main body of data supports the existence of a warm
region centered north of the island, while other data indicate an area of cold high-
salinity upwelling. A knowledge of the seasonal development of the water structure in
this area and its relation to the local wind conditions might resolve this apparent conflict.

Lastly, a gap exists in the data along the Alaskan Coast between Cape Lisburne
and Pt. Barrow. Although this region appears to have a simple coastal circulation,
a study of this area would be of value to tie in the Chukchi Sea work with that done
in the Beaufort Sea.

19 J. F, Holmes and L. V. Worthington Project SKIJUMP Conducted during the Period February-May
1951 (Woods Hole Oceanographic Institution, Reference no. 51-67) September 1951.

20 J. F. Holmes and L. V. Worthington Oceanographic Studies on Project SKIJUMP II (Woods Hole
Oceanographic Institution, Reference no. 53-23) April 1953.

TEMPERATURE (“F)

SALINITY (°/n).

7 @

SALINITY (°/o0)

230 25

aren

SALINITY (on)

3.3 7 Ww

SALINIT: ("/e0)

3 36 7 2 3

Bs 4S OD BD Os

Figure 8. Typical vertical distributions of temperature and salinity and T-S relation-

ships for selected stations.

TEMPERATURE (°F) TEMPERATURE (°F) TEMPERATURE ("F)
STATION 90 STATION 160, ‘STATION 108 STATION 51 STATION 194, STATION 201 STATION 708
ai * Tejera 3 To cy Jago) 5 Taal
ee ES SSS) Te ee Se
a ie Ht {
peeeeere HES SS a H Eee
gi ama | si] || EEN io} Aeenooe ig) <t Por
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qgaeeer far souseezeei ceseezece7e(Msetecer.eueMMatesaersess@lszerees, ze
7 1 2
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(Vert psu x BBP pica aes na pv» KH RDB (eee oes ae agen Teer 2 ar SOT aE SL a Sp 2 oD ee
SALINITY ("/) SALINITY (‘/e) SAUINITY ("/e) ‘SAUNITY ["/.) SAUNITY ("/.) SALINITY (/e)

21

SALINITY (°/co) SALINITY (°/oo) SALINITY (°/o) SALINITY (°/m) SALINITY (°/c)
23025 ee 27 aT eS 2a es 270 SY 33 23) 25 27 (29 (a1 33 223 2527 ast sa) eel ery Fae EVN ES

ae

SALINITY (°/00)
£2325 a7 eg es a

DEPTH IN FEET

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TEMPERATURE (*F) TEMPERATURE ("F) TEMPERATURE (*F) TEMPERATURE ("F) TEMPERATURE ("F) TEMPERATURE ("F)
STATION 35 NORTHLAND STATION 353 STATION 36 STATION 37 STATION 53 STATION 54
0 0 —— Oe E a Taal +— 0) T
15 L
re m { “ EE 4 Jt “ q,
= one ony ee . 1
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SALINITY (7a) SALINITY ("/a) SALINITY ("/a) SALINITY (Va) SAUNITY (Ya) SALINITY ('/=)

STATION

Figure 9. Woater-mass structure along a section from Wales fo Strait of Anadyr with
vertical temperature and salinity distributions and T-S relationships for selected stations.

8

c
=
=
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tH
a

g

30 MILES

a!

STRUCTURE

23

SALINITY (°/co) SALINITY (°/00) SALINITY (°/00), SALINITY (°/e0) SALINITY (°/co)
2237 29 NN 33 aesemwmeye HN 3 3236 7 2 HN 33 anasoeu#speenwis is aa vu pans

wD
1
Cae
wo
iv
&
Z 1
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iT y
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TEMPERATURE ("F)
’
NORTHLAND STATION 333 STATION 40 STATION 4 ‘ STATION 59 STATION 7
.

0 al 0 B That wD 2 ry T -
. lia “6 “4 {eed | 6 “4 et |
ra iP - -+ oa r)
5 a 0 Al a | TF a Si | a [I
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: | ; i SES CI ESBS i
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a r) nan a n E<) B Ba n =) n xn a nn x» z n J % D B ap » n n zB D 3B ed a» nu 2 zB
SAUNITY (/e) SALINITY (‘/-). SALINITY (*/) SALINITY ("/=) SAUNITY (/a)

Figure 10. Water-moss structure in eastern Bering Strait with vertical temperature and
salinity distributions and T-S relationships fer selected stations.

DEPTH IN FEET
8

ao so 7
STATION

25

TEMPERATURE (°F)

SALINITY (°/cn)

SALINITY (?/on)

SALINITY ("/on),

SALINITY (°"/o0) SALINITY (°/c)

nasoawywe2sei3s na 32.235 27 @ SH (3 3367 ww 8 33 23025 «27 2 31 KK} 3a 3s 7 2 33
0 0
~ el =
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Zw - t+
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eee W-
EEE EHH
190 {t 16g 190} i
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105 n 3 0 a“ a 15 n » 40 “a cy Ls n ey 0
TEMPERATURE (°F) TEMPERATURE ("F) TEMPERATURE ("F)
STATION 133, STATION 135 STATION 137 STATION 140, STATION 142
as a5 ou a | > el i) ia a [=ES=t=E ETS
oe] el Nat ae | a al jaan iH tet amt faye
A 9.
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SALINITY ("/a) SALINITY C/a) SALINITY ("/a)

Figure 11. Water-mass structure in the Kotzebue Sound region with vertical tempercture
‘and salinity distributions and T-S relationships for selected stations.

SALINITY ("/s)

STATION

27

Ppp ni imate

Seth

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aS
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eee! sp tien. <
SALINITY (°/0) SALINITY (°/on)
94° 28 a7) 39) 21 a3. 23) 2s ah 9 aN ad

TEMPERATURE (°F)

STATION 169 STATION 100 STATION 1 STATION 156
ja f I ° al
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Figure 12, Water-mass structure along a section northwestward from Cape Lisburne with
vertical temperature and salinity distributions and T-S relationships for selected stations.

STRUCTURE
70° N, 167° 25'W

IW)

DEPTH IN FEET

STATION

29

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B30 2502729 ts) 33 AS 25 a7 20d ss Fey fH Fy tre cht eS PY PL eh ED Ef ES 73252729 eS SS
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— 3 2 » “0 “4 es B n » “0 a“ a 3B 2 % «0 “a a
TEMPERATURE (°F) 3 TEMPERATURE (°F) TEMPERATURE (°F)

STATION 91 ‘STATION 67 STATION 162 STATION 160, ‘STATION 158
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vertical temperature and salinity distributions and T-S relationships for selected stations,

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NAVY — NEL San Diego, Calif.