TR-221

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TECHNICAL REPORT
MAJOR CURRENTS
OFF THE WEST COASTS
OF NORTH AND SOUTH AMERICA
OCTOBER 1969
GC
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‘ R- NAVAL OCEANOGRAPHIC OFFICE
hb. 1K- 3 ‘| WASHINGTON, D. C. 20390
| Price 60 cents

ERRATA

TR-221, ''Major Currents off the West Coasts of North and South America!??

page v, Contents; for El Nino read El Nino

page 7, Table 1, Region F, last line; for MME read NNE

page 14, Table 3, left column; for 40° to 50°N read 40° to 48°N

MIN

In

Min

(NN

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FOREWORD

This report is intended to help meet a need for the identification
of the major currents off the west coasts of North and South America
and a comprehensive summary of their principal characteristics. The
information given herein is based on published reports and directly
measured data, as well as considerable unpublished data, of which a
large amount has recently been obtained. Much of these data has been
analyzed specifically for this report.

This is the second of a planned series of three reports. The

first includes descriptions of the currents of the North and South

L7-She

F. L. SLATTERY

Captain, U. S. N
Commander

Naval Oceanographic Office

Atlantic Oceans.

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Foreword . « e« »
List of Figures
List of Tables .
Introduction °
Alaska Current .

Bering Current .

e

California Current

Cape Horn Current

Davidson Current
El Nino . » « e«
Mentor Current .
Peru Current . »
Conclusions . »

References Sate

CONTENTS

LIST OF FIGURES

Surface currents north of 50°N. = 2 2 » « = ©. = = lsus
Schematic diagram of Alaska Current . »« « » » « « « «© « e
Subsurface current speeds in Bering Strait ...+.«»o»-.
Boundaries of California Current. . « « « » » » « «© «© «© &
Computed current speed profiles, Cape Horn Current . » «
Observed current profile, Cape Horn Current . « « « « » »
Boundaries of Davidson Current ..» « « e « © e « « « « »
Directions, speeds, and boundaries of Mentor Current ..
Surface and subsurface flow of Peru Current . » « » « e e

Upwelling and weakening of Peru Current . » « « « » « « »

LIST OF TABLES

Directions and speeds of Alaska Current in regions shown
abo Walfeee) DL 5G 5b OOO OOOO COO OC Oe

Surface and near-bottom currents off the coast of

INIA BH BODOG OOOO OO OO Oe ROO Oooo Oo
Directions and speeds of California Current . . . » » » e

Directions and speeds of Davidson and California
Currents Oo Bi we Oh Je a ei 8) eo Peete enue. 6) 6) (eumel ee rerien lane,

Offshore winds in the vicinity of }O°N ......s.se-s

Vi

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22

MAJOR CURRENTS OFF THE WEST COASTS OF
NORTH AND SOUTH AMERICA

Introduction

The descriptions of eight principal currents in this report are
based mainly on data obtained by direct methods in regions from the
Bering Sea to Cape Horn. Except for the Peru and Cape Horn Currents,
surface flows appear to be il] defined and exhibit characteristic
variability.

The usual graphic presentation of ocean currents is, at best,

a static picture. The surface of the ocean is in constant motion,

the movement being exceedingly variable in some regions and relatively
constant in others. The currents described in this report are those
where the movement within specified boundaries exhibits a permanent

or seasonal flow. The regions beyond the boundaries of the currents
are those where flows, frequently considered part of the prevailing
current, are less defined, described from insufficient data, mainly
tidal, under the influence of winds or river discharge, or variable
and turning. The boundaries indicate gradual change between zones of
more persistent flow and zones of less stable or weaker flow.

The approximate boundaries and the main body of each current
shown are based on ship drift observations and direct measurements
by instrument, which describe the two main features of the current,
namely, direction and speed. Dynamic topography presentations are
mentioned or shown only where they might prove of interest by

comparison with results of direct measurements.

ALASKA CURRENT

Surface current data in the Gulf of Alaska are scarce and
unevenly distributed; of almost 9,000 observations north of 50°N,
about 6,700 are located in regions A, B, and D of Figure l.
Inasmuch as the southern boundary of the Gulf of Alaska is north
of 55°N, regions A, B, and D may be considered outside the gulf,
and the persistence of the eastward flow through these regions is
due mainly to the influence of the Subarctic Current.

The Alaska Current actually originates from the part of the
Subarctic Current that is diverted north in the vicinity of Queen
Charlotte Islands, and is a slow, wide, counterclockwise flow
along the coast to about 170°W. The current appears to be somewhat
faster in regions G and H (Figure 1) than elsewhere.

Figure 1 and Table 1 indicate the general flows in the gulf;
significant frequencies of flow in other directions also are shown
in Figure 1. The shaded outlines show that the Alaska Current is
weak, with little seasonal change in mean speeds, so that it is
easily influenced by strong winds associated with frequent storms
through the gulf, particularly from September through May.

The data in Figure 1 and Table 1 are based on surface ship
drift observations and show a very close directional relationship
with the computed surface flow and with the schematic shown in

Figure 2.

LEGEND
THE SHADED PART OF ROSE SHOWS DISTRIBUTION OF DATA INTERPOLATED
BETWEEN EIGHT COMPASS POINTS; ITS SHAPE INDICATES GRAPHICALLY THE
VARIABILITY OF FLOW.

EACH DIVISION ON A DIRECTION ARM INDICATES 2 PERCENT FREQUENCY AND
0.1 KNOT

THE ARROW SHOWS PREVAILING DIRECTION AND MEAN SPEED

NUMBER AT LOWER RIGHT OF ROSE SHOWS NUMBER OF OBSERVATIONS.

APR. MAY JUNE JULY AUG SEPT. OcT. NOV. DEC. JAN. THROUGH DEC.

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FIGURE 1 SURFACE CURRENTS NORTH OF 50°N
3

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‘ ocr 1) P< fh Te .

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Spine 204

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AUG. . JAN, THROUGH DEC.

FIGURE 1 SURFACE CURRENTS NORTH OF 50°N, CONTINUED
5

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INGuunNd VASVIV JO WVUDVIC OILVNYHOS ¢ qHHNSIA

oO0El oOVl OSI 091 oOLI oO8l

BERING CURRENT

Sparse available data indicate a general north-flowing current
through the eastern half of Bering Sea, through Bering Strait, and
in eastern Chukchi Sea. The current originates mainly from the
North Pacific Current, and its speed in the Bering Sea is estimated
to be usually 0.5 knot or less but at times as high as 1.0 knot.

In Bering Strait current speeds frequently reach 2 knots;
however, in the eastern half of the strait currents are even
stronger and usually range between 1.0 and 2.5 knots. The volume
transport of the prevailing northward flow in the strait during
August was computed to be about 120 km3 per day. Strong southerly
winds may increase current speeds in the strait to 3 knots, and
up to 4 knots in the eastern part; persistent strong northerly
winds during autumn may cause the current to reverse for short
periods. During winter a southward flow at times may occur in
the western part of the strait.

After flowing through Bering Strait, the current widens, and
part continues toward Point Barrow, where it turns northwest.
Table 2 shows prevailing directions and speeds at the surface and
near the bottom observed in August at 22 locations in the eastern
part of the shallow Chukchi Sea, where 31 current meter stations
were occupied. Along the Alaska coast, current speeds have been
observed to range between 0.1 and 1.5 knots and increase to 2.0
or 2.5 knots with southerly winds. In the western part of the
Chukchi Sea, currents are considerably weaker and do not usually

exceed 0.5 knot.

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10

Figure 3A is a composite of 15 current stations in August in
the eastern part of Bering Strait; the flow ranges between
west-northwest and north-northeast and indicates persistent speeds
ranging between 0.2 and 2.1 knots. Figure 3B is a composite of eight
current stations in the western part of the strait; the flow there
is weaker but still persists between west-northwest and north between
O.4 and 1.4 kmots. The current in the Chukchi Sea is augmented by the
Hast Siberian Coastal Current, which joins the north-setting Bering
Current north of East Cape.

Northeast of Wrangel Island, in the vicinity of 72°N, 175°W,
five current meter stations showed the current to be outside the
limit of the northeast flow. The current near the surface appeared
to be mainly tidal, changing direction periodically; the tidal
effect lessens considerably to a depth of 40 meters and disappears

near the bottom.

DEPTH (METERS)

DEPTH (METERS)

SPEED (KNOTS)

0.0 : ; ‘ : TOL 2g 4 : f ‘ ; 2.4
0
25
50 Y
65.7°N , 168.5°W AUGUST 1955, 1960, 1964
0)
25
50
7 BOTTOM Y
65.7°N , 169.6°W AUGUST 1964

FIGURE 3 SUBSURFACE CURRENT SPEEDS IN BERING STRAIT

CALIFORNIA CURRENT

Usually described as a permanent ocean current, the California
Current is actually a poorly defined and variable southerly flow
easily influenced by the wind. Figure } shows the boundaries
within which the southward flow is observed, particularly during
March through September when the current extends to the coast and
includes the region usually occupied by the Davidson Current during
winter. Table 3 indicates the variability of flow of the California
Current by season in regions A and B, and for the months when the
current is observed in coastal regions C and D. Part of the
south=-setting California Current is observed within the near-coastal
Davidson Current during winter.

It is evident from these data that even during summer, when
the California Current is most constant, it tends to be variable.
In region A the current sets directly south 23 percent of the time;
all other directions average about 10 percent. In region B the
current sets generally southeast through south to southwest 58
percent of the time; other directions average 8 percent.

During winter in region A the current sets directly south only
about 19 percent of the time; it has little stability as
significant percentages of observations indicate north, east,
southeast, and west flows. In region B the current sets generally
southeast through south to southwest about 48 percent of the time;
other directions average 10 percent, with no significant secondary
flow.

The minimum flow of 19 percent southward in region A during

winter coincides with the winds in the vicinity of 40°N, which

13

Prevailing current [Secondary current [ |
Knots Knots
Dir
bea [oe bs eee

Region A

Dec.-Mar. Variable

Apr.-Sept. Variable

Region C

Mar.
Apr.
May
June
July
Auge
Sept.

Region B
Dec.-Mare

Apr e-Septe Variable

Variable
Variable

s
s
Ss
s
s
iS}
s
5
s
s
Ss
Ss
8

UNITED| STATES

FIGURE 4 BOUNDARIES OF CALIFORNIA CURRENT

14

dominate from southeast through southwest during December and
January only; winds prevail from northwest and north-northwest
in all other months.

In region C the flow is definitely south from March through
September; flow is more constant, percent frequencies are higher,
and speeds are stronger than in region D, where flow is more
variable. The southward flow is most constant in region D during
July, although the frequency is only 25 percent compared to less

than 13 percent in any of the other seven directions.

CAPE HORN CURRENT

The Cape Horn Current sets continuously eastward close to the
tip of South America and enters Drake Passage at about 7O°W ina
150-mile-wide band, with surface speeds up to 2.4 knots. The set
veers north-northeast, and when it crosses longitude 65°W the
eurrent has narrowed to a width of about 85 miles and its speed
has decreased considerably.

The profiles of computed speeds in Figure 5 show the
well-defined limits of the current. Available data indicate a
fairly high rate of transport for this current, averaging about
370 x 107 m3/hr in the western part and 22h x 109 m3/hr in the
eastern part.

The current profile shown in Figure 6 indicates the usual

range of speed and the set that can be expected in Drake Passage.

16

820

Y
Z

1,640
a 7) Y 2460
ch to Z 3,280 im
Z SoG a0
= = Y 4920 ~
x 36 Y a
E E Y, 6560 @&
So ra) Y 8,200 0
) 9,840
7 11,480
NOTE CHANGE NOTE CHANGE
IN INTERVAL. IN INTERVAL.

LEGEND

STATION LOCATION

» APPROXIMATE BOUNDARY
OF CAPE HORN CURRENT

LIMITS OF CROSS SECTION
CURRENT SPEED (CM/SEC )

FIGURE 5 COMPUTED CURRENT SPEED PROFILES, CAPE HORN CURRENT

DEPTH (METERS)

SPEED (KNOTS)
hee 0:2) .OFAP 06 058 EO 12 A eOmn eS euere Once 2%

25 82

50 164

100 328

200 656

400 1312

800 LEGEND -
RANGE OF OBSERVED SPEED
PREVAILING DIRECTION

: DEPTH OF OBSERVATION
nes : MEAN POSITION:
y LAT. 56°43’S, LONG. 66°09’W

MARCH 1963-64
MEASURED BY BUOYANT FLOATS

3200 DEPTH OF BOTTOM 3780 M 10496

UMMM

5248

6400 20992
FIGURE 6 OBSERVED CURRENT PROFILE, CAPE HORN CURRENT

18

DEPTH (FEET)

DAVIDSON CURRENT (Winter Coastal Countercurrent)

The Davidson Current is not a permanent ocean current but
rather a seasonal countercurrent that sets northward at all depths
close to the Pacific coast of the United States north of 32°N.
Available data indicate that this flow should be more accurately
referred to simply as the Winter Coastal Countercurrent; it is a
poorly defined and variable flow dependent mainly upon the
influence of the wind.

Figure 7 shows the boundary within which the prevailing
northward flow most frequently occurs; it becomes best established
in January. Table } indicates the variability of flow by showing
the monthly percent frequency of observations of speed and direction.
The Davidson Current is interrupted by the prevailing south flow of
the California Current from March through the first half of October.

The southern part of the Davidson Current, region B, is more
variable than the northern part; although the prevailing flow is
northward during winter, the data show that sets in the opposite
direction occur frequently in January and February. During July,
under the influence of the California Current, the southward flow
is most constant although the frequency is only 25 percent compared
to less than 13 percent in any of the other seven directions. Calms
average 8 percent and are twice those in region A, where the flow is
more constant.

In region A the current turns from south to north during
October, when considerable variability occurs; the northward set
increases in constancy through January, when the frequency of

southward sets is about 17 percent. The current appears to set

19

northward through the early part of February and then to become
variable as it begins to turn, as indicated by the distribution of
east and south flows totaling about 36 percent. From March

through September the strong southward flow is an extension of the
California Current; percent frequencies are higher and speeds are
stronger than in region B. The tabulated data indicate that part
of the south-setting California Current is also observed throughout
both regions during winter.

The pronounced northward flow in winter coincides with the
winds in the vicinity of 40°N, which predominate from southeast
through southwest only during December and January; they prevail
from narthwest and north-northwest in all other months. Table 5
shows the winds which can influence the current off the west coast
of the United States in December. The more frequent south and
southeast winds in region A will increase the constancy of the
north-setting current, whereas the more frequent northwest and north
winds an region B will cause the current to be more variable.

Drift bottles were released off the coast between 42° and
46°N between June 1959 and October 1963. The results generally
agree with the surface drift data in Table 4; over 70 percent of the
returns were from bottles released within 40 miles of shore, and
the northward flow was apparent during November through February in
all years.

Direct surface current measurements during March have indicated
a southeast flow within 30 miles of shore in the vicinity of

36°30'N, 122°15'W; in this region subsurface drogue measurements at

20

23 20%

TABLE 4 DIRECTIONS AND SPEEDS OF DAVIDSON AND CALIFORNIA CURRENTS

REGION PREVAILING CURRENT SECONDARY CURRENTS
A. }o°-48°N| DIR. % Mn. Max. DIR. % Mm. Max.

Knots Knots
0.6 1.9 s We) Osan ala
N 29 0.6 1.6 E Ue) @a5 Wo3}
Ss ig, Oak os)
Ss O45 2a N 19 ©-5 AO
s Oy - es sin iG Ox dicts)
s 0.6 2.0 N 1 ©.5 U6
s 0.6 1.6 SH yf @4G ei
45° Ss Oni das gi Wh 5 LSS
s Os WS N @o5 cI
Ss OG 66 E Ok O.6
s O45 o> E On5 1.0
N Oo5 U2 W Osh Oa
N @s5 asi Ss @gk aaw
N 0.6 1.4 s O4 0.9
other directions

less than 16% --

565

" 14% pers

u y 13% 529

4.96

Ww WW 13% aS

40°

35." 355

Pes UPL
125° 120°

FIGURE 7 BOUNDARIES OF DAVIDSON CURRENT

21

250 meters showed a northward flow about 40 miles wide at speeds

of about 0.5 knot. These seem to verify various reports that there
is a northward flow inshore throughout the year at depths below 200
meters. Above 200 meters the north-setting countercurrent that
develops when winds weaken or are southerly appears to be part of
the deep countercurrent.

When northerly winds become weak or negligible in late autumn
and winter, a north-setting countercurrent forms at the surface well
inshore of the main south-setting California Current. During this
period upwelling lessens and numerous irregular eddies may occur
along the coast. There is evidence that the nearshore countercurrent
may be influenced by coastal tidal currents observed from 5 to 20
miles offshore; these tidal currents are rotary and change direction
continually, so that during a tidal cycle they will have set in all
directions of the compass, with speeds varying according to lunar

phase or wind effect.

TABLE 5 OFFSHORE WINDS IN THE VICINITY OF 40°N, DECEMBER

REGION A REGION B

DIR. MEAN
FROM % SPEED (KN)

Dir. MEAN
FROM % SPEED (KN)

22

EL NINO

The name El Nino is generally identified with large-scale
disturbanees which occur in the northern part of the Peru Current
in certain years, reported to be at intervals of about every seven
years. However, El Nino is believed to be a local term for a
current that has been observed in late December for many years.

In December the northerly winds blowing across Central America
reach farther south and drive water from the Gulf of Panama southward
along the Peru coast. This current flows southward in a tongue-shaped
band 1 to 2 miles wide between 3° and 6°S. The intensity of this
phenomenon increases considerably in some years and influences a
larger part of the northern nearshore portion of the Peru Current.
During such periods the Peru Current retards, the temperature of the
surface water rises sharply, and the southward flow comes as far as
20°S. This condition, most commonly referred to as El Nino, results
in a layer of warm water about 75 feet deep and as wide as 20 miles.

Although the origin of this flow is not definitely known, it
is believed that northwesterly winds that penetrate farther south
than usual cause the Peru Current to weaken; close to shore a
south-setting flow develops as the cool Peru Current is replaced
by warm water with characteristics similar to those of the Pacific
Equatorial Countercurrent. Mass mortality of marine organisms
results when the cold and warm waters coverge.

The southward excursion of El Nino is most prevalent in
January through March, when it is halted by the reappearance of

southeasterly trade winds and the re-establishment of upwelling

23

along the coast. The complicated pattern of upwelling and wind
results in variable current speeds between zero and 1.5 knots near
13°42'S and a mean speed of 0.4 knot between 22°36! and 33°00'S.
Countercurrents may occur near shore.

Years during which El Nino has been recorded with greater
than usual intensity are: 1891*, 1911, 1918, 1922, 1925*, 1932,

1939, 1941*, 1953, 1957, 1965, 1967.

*Exceptionally strong

24

MENTOR CURRENT (Peru Oceanic Current)

The Mentor Current, named after the German ship that observed
it in 1833, originates mainly from the easternmost extension of
the South Pacific Current (located north of the West Wind Drift)
at about 40°S, 90°W. It sets north and northwest and has the
characteristic features of a drift in that it is a broad, slow-moving
flow that extends about 900 miles westward from the Peru Current to
about 90°W at its widest section and tends to be easily influenced
by winds. It joins the west-setting South Equatorial Current and
completes the anticyclonic movement in the eastern part of the
South Pacific Ocean. The speed in the central part of the current
at about 26°S, S0°W may at times attain about 0.9 knot.

A seasonal current rose for a region within the center of the
current, shown in Figure 8, indicates a significant percent
frequency of westward flow, which becomes greater westward as current
speed decreases. Comparison of this rese with the rose for region 2
in the adjacent Peru Current shows the differences in speed and
direction between the two currents.

Very little is known of deepwater flow in the eastern South
Pacific Ocean, and estimates of speed and volume transport are
necessarily approximate. Indirect observations made at a depth of
3,500 meters in the southern part of the Mentor Current at about
39°S, 84°W indicate a probable weak, uniform movement northward up
to 0.05 em/sec; volume transport of Pacific deep water from the

Antarctic is estimated at about 15 x 10° m/sec.

25

OEP Or ier BOP 7sP

10°

REGION \
OF ROSE

30°

ep OOP Eee BOP 7”

o°

10°

20°

30°

0 10 20 30 40 50 60 70 80 90 100
40° ROSE SCALE (PERCENT)

LEGEND
FREQUENCY SUMMER (OCT.—MAR.)

FREQUENCY WINTER (APR.—SEPT.)

SUMMER
WINTER
SUMMER
WINTER

MEAN SPEED (KNOTS)

TOTAL OBSERVATIONS

— — — CURRENT BOUNDARY

FIGURE 8 DIRECTIONS, SPEEDS, AND BOUNDARIES OF MENTOR CURRENT

26

PERU CURRENT (Peru Coastal Current, Humboldt Current)

The Peru Current is a narrow, fairly stable current that flows
northward close to the South American coast. Knowledge of this
current dates from 1522, and its nomenclature has been confused for
years; the original synonymous term "Humboldt Current," based on
Humboldt's observations in 1802, may be more appropriate since the
current originates from the central portion of Chile at about 40°S
and flows past Peru and Ecuador to the southwest extremity of
Colombia.

The Peru Current has been identified as occupying two distinct
regions; the inshore current often is referred to as the Peru
Coastal Current, and the offshore current is described as the Peru
Oceanic Current. However, these terms have been used arbitrarily, and
the distinction is made principally from the biological characteristics
in the upper layers. In this report the Peru Current is shown in
Figure 9, and the limits are based on persistence and speed derived
from thousands of surface drift observations.

Although identified in some references as the most outstanding
eurrent in the Southern Hemisphere, the Peru Current is not very
strong but has a mean speed of 0.9 knot in the northern region where
the flow is most persistent. The surface flow extends to about 300
meters, and the volume transport is estimated to be 26.8 x 106 m/sec
at about 5°S.

The Peru Current is a relatively cool flow that originates from

water of the South Pacific Current and the West Wind Drift where these

27

STATION DEPTH
320 M

CM/SEC
OCTOBER

MAZ6
R
By Me

STATION DEPTH
300 M

OCTOBER

Co
Cegccceces
cone

STATION DEPTH
650 M

NOVEMBER

STATION DEPTH
3135 M

Y
100 M
250M

CORRECTED SUBSURFACE MEAN CUR-
RENT VECTORS. INTERMEDIATE VEC-
TORS AT 100 AND 150 METERS
SHOWN BY DASHED LINES. DEEP
VECTORS AT 250 AND 300 METERS
SHOWN BY SOLID LINES. 100-METER
VECTOR AT STATION C NOT TO
SCALE (SPEED 15 CM/SEC).

7/0

80°

90°

0°

iKO}=

40°

LEGEND

exes CURRENT BOUNDARY

@A
9 REGION OF ROSE ON PAGE 29

SUBSURFACE CURRENT STATION

| FIGURE 9 SURFACE AND SUBSURFACE FLOW OF PERU CURRENT

28

REGION 1
MM, SEPT. THROUGH APR.
[7 MAY THROUGH AUG.

318
slo

REGION 4
MMM SEPT. THROUGH APR.

([=7] MAY THROUGH AUG.

as
clo

REGION 7
Ms JAN. THROUGH MAR.

[=] JULY THROUGH SEPT.

oO
Nog
&

pars
olo

REGION 10
ME OCT. THROUGH MAR.

[=] APR. THROUGH SEPT.

REGION 2
GER SEPT. THROUGH APR.
[= MAY THROUGH AUG.

REGION 5

OCT. THROUGH MAR.

[7 APR. THROUGH SEPT.

REGION 3
GR SEPT. THROUGH APR.

[277] MAY THROUGH AUG.

REGION 6
GROOT. THROUGH MAR.

[=] ApR. THROUGH SEPT.
es
°s

ale
Slo

REGION 8
GRR (JAN. THROUGH MAR.

[J JULY THROUGH SEPT.

Be -
colo

REGION 11

GR). JAN. THROUGH MAR.
[=] JULY THROUGH SEPT.

CONTINUED

10 20 30 40 50 60 70 80 90

ROSE SCALE (PERCENT)

29

a2
clo

REGION 9
GOO. THROUGH MAR.
[= APR. THROUGH SEPT.

LEGEND

MEAN SPEED (KNOTS)

TOTAL OBSERVATIONS

froapaeiprorgonapeenpsonappseepanrp|

100

FIGURE 9 SURFACE AND SUBSURFACE FLOW OF PERU CURRENT,

flows pass into the region of the trade winds. The current follows
the coast and joins the Pacific South Equatorial Current beyond
100°W.

The surface current shows a high constancy throughout the
greater part of its length and is little affected by latitude or
season. What seasonal variation does occur is shown in the surface
current roses in Figure 9; the current tends to be most variable
south of 10°S during the southern winter and north of 10°S during
the southern summer. The current most frequently flows at speeds
ranging between 0.2 and 1.4 knots, being strongest off the Peru
coast; maximum speeds occur at its northern extremity between the
continent and the Galapagos Archipelago. The currents are stronger
near shore and weaken with increasing distance from shore.

In some regions, however, the current is very weak, with eddies
occurring at irregular intervals; south-setting countercurrents
frequently flow close to shore as indicated by the south component
of the surface current roses, Because of the moderate speed and
variability of the Peru Current, its exact west boundary is
difficult to determine; the flow west of the Peru Current is also
markedly northward, and there is no sudden change between the
coastal zone of more persistent flow and the oceanic region of less
stable or weaker flow.

Observations have shown that the current close inshore is
under the nearly continuous influence of small-scale upwelling

(Figure 10). Steady southerly winds along the coast tend to force

the surface water offshore and produce continuous vertical circulation.
Upwelling occurs between about 30° and 5°S as shown in Figure 10 and
is limited mainly to the upper 200 to 300 meters. South of 15°S,
upwelling is less intense.

Results of direct current measurements indicate a southward
subsurface flow along the edge of the Continental Shelf at depths
below 300 meters between northern Peru and at least as far south
as }1°S. Off Peru and northern Chile, speeds to 0.4 knot were
recorded; like the surface current, the speed of this undercurrent
is weaker in the southern part of the Peru Current, especially
south of 15°S. Figure 9 shows results of direct subsurface current
measurements at four locations within the Peru Current.

Volume transport of this undercurrent has been computed at
about 21x 106 m3/sec at 5°S, decreasing to about 3 x 106 m3/sec
at 15°S. The decrease in volume of southward flow occurs mainly
in the region of strongest upwelling and may be due to continual

loss through vertical and horizontal transport.

31

LEGEND

ZONE OF UPWELLING AND
CURRENT INTENSIFICATION

(AN ZONE OF CURRENT WEAKENING

FIGURE 10 UPWELLING AND WEAKENING OF PERU CURRENT

32

Conelusions

An examination of existing data sources clearly shows that the
methods utilized to determine the principal characteristics of ocean
currents leave much to be desired. From the many and varied types
of information available, it is obvious that detailed, accurate
descriptions of currents cannot be readily obtained and that some
currents will continue to be better known than others.

It is generally agreed that ocean current information is very
sparse and usually insufficient for most ocean areas. Where there
are sufficient ship drift observations, satisfactory current patterns
can be derived; the number of reliable current meter measurements
at sea is negligible. As more and better data become available,
the descriptions of the currents in this report can be refined to

a greater degree of precision.

REFERENCES

Earland, Arthur, et al. 1936. Discovery Reports. Cambridge
University Press. 13: 1-384.

Fleming, Richard H. 1961. Physical and chemical data for the
Hastern Chukchi and Northern Bering Sea. University of
Washington, Department of Oceanography Tech. Rpt. No. 69,
kop.

Gierloff-Emden, Hans Gunter 1959. The Humboldt Current and the
Pacific land area of its effective range. Special issue of
Petermann's Geographical Reports. 1. Quarter, leipzig,

170) | IAL

33

Knauss, J. A. 1962. On some aspects of the deep circulation of

the Pacific. Journal of Geophysical Research.
67(10): 3943-54.

Reid, J. L. 1962. Measurements of the California countercurrent
at a depth of 250 meters. Journal of Marine Research. 20(2):
134-137.

Reid, J. L. and Schwartzlose, R. A. 1962. Direct measurements of
the Davidson Current off Central California. Journal of
Geophysical Research. 67(6): 2491-97.

Sverdrup, H. U. 1931. Some oceanographic results of the CARNEGIE'S
work in the Pacific. The Peruvian Current. The Hydrographic
Review. 8: 20-2,

Sverdrup, H. U. 1929. The Waters on the North Siberian Shelf. ‘The
Norwegian North Polar Expedition with the "Maud," 1918-1925,
Scientific Results, Vol. IV, No. 2, Geofysisk Institutt, Bergen,
A. S. John Griegs Boktrykkeri, Bergen.

PADD Vi Ec) Bis 1941. The water masses off the west coast of North
America. Journal of Marine Research. (2): 112-121.

Vallaux, C. 1930. The question of the Humboldt Current. Was
Hydrographic Review. 7(1): 66-74.

Wooster, W. S. and Gilmartin, M. 1961. The Peru-Chile undercurrent.

Journal of Marine Research. 19(3): 97-122.

34

U.S. Naval Oceanographic Office

MAJOR CURRENTS OFF THE WEST COASTS OF NORTH
AND SOUTH AMERICA by William E, Boisvert, 37p.
including figures, (TR-221)

Bibliography p 33.

This technical report presents a description of eight
principal currents in various regions from the Bering
Strait to Cape Horn,

U.S. Naval Oceanographic Office

MAJOR CURRENTS OFF THE WEST COASTS OF NORTH
AND SOUTH AMERICA by William E. Boisvert, 37p.
including figures, (TR-221)

Bibliography p 33.
This technical report presents a description of eight

principal currents in various regions from the Bering
Strait to Cape Horn,

1. Currents-West Coasts of North and
South America
2. Wests Coasts of North and South
America-Currents
3, Alaska Current
4, Bering Current
5, California Current
6, Cape Horn Current
7, Davidson Current
8. El Nino
9, Mentor Current
10, Peru Current
i. title: Major Currents off the West
Coasts of North and South America
ii. author: William E, Boisvert
iii, TR-221

1, Currents-West Coasts of North and
South America
2. Wests Coasts of North and South
America-Currents
3, Alaska Current
4, Bering Current
5, California Current
6, Cape Horn Current
7, Davidson Current
8, El Nino
9, Mentor Current
10, Peru Current
i, title: Major Currents off the West
Coasts of North and South America
ii. author: William E. Boisvert
iii, TR-221

U.S. Naval Oceanographic Office

MAJOR CURRENTS OFF THE WEST COASTS OF NORTH
AND SOUTH AMERICA by William E. Boisvert. 37p.
including figures, (TR-221)

Bibliography p 33.

This technical report presents a description of eight
principal currents in various regions from the Bering
Strait to Cape Horn,

U.S, Naval Oceanographic Office

MAJOR CURRENTS OFF THE WEST COASTS OF NORTH
AND SOUTH AMERICA by William E. Boisvert, 37p.
including figures, (TR-221)

Bibliography p 33.
This technical report presents a description of eight

principal currents in various regions from the Bering
Strait to Cape Horn,

1. Currents-West Coasts of North and
South America
2, Wests Coasts of North and South
America-Currents
3, Alaska Current
4, Bering Current
5, California Current
6, Cape Horn Current
7, Davidson Current
8, El Nino
9. Mentor Current
10, Peru Current
i, title: Major Currents off the West
Coasts of North and South America
ii. author; William E. Boisvert
iii, TR-221

1. Currents-West Coasts of North and
South America
2. Wests Coasts of North and South
America-Currents
3. Alaska Current
4, Bering Current
5, California Current
6. Cape Horn Current
7. Davidson Current
8. El Nino
9, Mentor Current
10, Peru Current
i, title: Major Currents off the West
Coasts of North and South America
ii. author: William E. Boisvert
iii, TR-221

Wh ee aS

“er oa

Unclassified

Security Classification

DOCUMENT CONTROL DATA-R&D

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U.S. Naval Oceanographic Office
Washington, D.C. 20390

3. REPORT TITLE

MAJOR CURRENTS OFF THE WEST COASTS OF NORTH AND SOUTH AMERICA

5. AUTHOR(S) (First name, middle initial, last name)

William E. Boisvert

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TR- 221

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none U.S. Naval Oceanographic Office

The descriptions of eight principal currents in this report are based on
data obtained by direct methods in regions from the Bering Sea to Cape
Horn, Except for the Peru and Cape Horn Currents, surface flows appear
to be ill defined and exhibit characteristic variability. The usual graphic
presentation of ocean currents is, at best, a static picture. The surface of
the ocean is in constant motion, the movement being exceedingly variable
in some regions and relatively constant in others. The currents described
in this report are those where the movement within specified boundaries

exhibits a permanent or seasonal flow.

FORM GE
D D 1 NOV aul 4 73 pr A Unclassified
Security Classification

S/N 0101-807-6801

Security Classification

KEY WORDS

Currents

North America
South America |
Alaska Current

Bering Current

California Current

Cape Horn Current

Davidson Current

El Nino

Mentor Current

Peru Current

>) FORM
DD 1 NOV 21473 (BACK ) Unclassified

(PAGE 2) Security Classification