OCEANOGRAPHIC INVESTIGATION IN THE CHUKCHISEA DURING THE SUMMER OF 1958
KEIJI NASU
INTRODUCTION

This paper is the result of investigation conducted by the author in thewaters of the Chukchi Sea (Arctic Ocean) during August of 1958. Thisobservation was carried out on board of the "Fumi-maru No. 16 ", belonging to the Taiyo Fisheries Co., Ltd.
The observation in the Chukchi Sea has begun in Aug. 16, and completed in Aug. 20. During the season, 19 stations were occupied, covering the region shown by Fig. 1.
At each oceanographic station, the records of vertical temperature
distribution were obtained from bathythermograph. Planktons werecollected almost at all stations and sediments of the bottom were taken

66
67

•

68°

•

65

•

64

•

62

68

•

•

CHUKCHI S~A

69

•

61
70

•

67°

•

..

71

60

•

72

• 73

59

•

Fig. 1. Location of bathythermograph stations (56-74) and hydrographic stations
established by the U.S.C.G.C. Chelan in 1934 (36-39).
143

144

KEIJI NASU

at St. 59, 63 and 69 only. Furthermore, a sample for measurement ofradio-activity was taken at St. 70.
Materials gathered at the surface include observation of temperatureand of chlorinity, dissolved oxygen and hydrogen-ion concentrations of
the waters.
The author wishes to express his thanks to Captain Sumio Tanaka
and Mr. Eiichi Tanaka, the members of the Taiyo Fisheries Co., Ltd.
and the crew on board of the "Fumi-maru No. 16 ", who helped him
during the season.
The author is greatly indebted to Dr. Michitaka Uda, Professor of
the Tokyo University of Fisheries, who gave me many kind advices andread through the paper, and to Dr. Hiroshi Niino, Professor of the Tokyo
University of Fisheries, who examined samples from the sea bottom.
Thanks are also due to Mr. Katsuo Ohkubo, a member of the TokaiRegional Fisheries Research Laboratory, who measured radio-activity of
the waters.
TEMPERATURE AND SALINITY

Fig. 2 shows the distribution of temperature and salinity at the sea surface. Temperature and salinity at the surface in the Chukchi Sea obtained by the survey, ranged from 3.7°C minimum to 11.2°C maximum.
The maximum temperature area located at the WSW off Point Hope,and the isotherms in that area run quite similar to the contour line in
the topographical distribution.
Isohaline at the surface, 31.50%0 line, runs parallel to the Alaskan continent. In general, in the eastern area of the Chukchi Sea, the surface
sea condition tends to higher temperature and lower salinity, and those
isoplethes run in paralleled with the Alaskan coast line as already stated by
La Fond & Pritchard (1952). It is especially conspicuous off Point Hope.
In addition, the warm and low salinity water may be considered as
due to the influence of heating by solar radiation on ice-melted water.
The distribution of water temperature at the surface in the Chukchi Sea
is characterized by a decrease from the east to the west. On the other
hand, the distribution of salinities show increase from the east to thewest and its maximum, 32.00%0 located at near 170°-172°W on 68°20'N
line. The values of salinity decrease from the higher saline area to
the Siberian coast, where the water masses are modified into these lessthan 5.0°C in temperature and 30.00%0 in salinity.
The high salinity in the central part of the Chukchi Sea may be dueto the influence by the northward current from the Bering Strait, inthe adjacent waters to the Siberian coast. While the low saline water

OCEANOGRAPHIC INVESTIGATION IN THE CHUKCHI SEA

Fig. 2.

145

Horizontal distribution of temperature and salinity at surface.
Solid line-temperature.
Broken line-salinity.

may be due to the melting ice and the inflow of coastal waters.
From the distribution of temperature and salinity the cyclonic eddy
seems to be located in the vicinity of 66°40'N, 170°W. In addition, thecoldest portion is found in the north of the Anadyr Bay and its temperature at the surface is below 2.5°C. It seems that the coldest area
exists stationary.
In the eddy area near to 66°40'N, 170°W, origin of southward current is considered as the Bering water mass, and northward directionof flow for east of the Diomede Islands. That is, from distribution of
surface temperature as denoted by G. Ratmanoff (1939) northward current is affected by the cyclonic eddy of large scale located near to67°30', 170°W and its flow extends to southward.
The cold water mass along the Siberian coast flows with speed ofabout 1 knot (G. Ratmanoff, 1939) and it formed oceanic front with thenorthward Bering water mass. Moreover, observation from the vessel
many foams were recognized on the front. It is clear that thecollision of those water masses was remarkable at its situation of thefront. Comparatively value below 6.0°C was found at near 66°40'N,

146

KEIJI NASU

'l,,-,, \\
\ \

67°

~'\

,////,\

67°\ \ '\ '\3!13.0
:
I

I
'.

I

I

I

I

3·0

I

I

I

I

I

5.0 4.s

66°

66°

Qo

~N 1~75__ __ , __ __ . ._ _- " -_ __ . __ _ _1~70__ __ . __ __ . __ __ . _ _ . . . _ , __ _~1~65°W~N
00Fig. 3.

Horizontal distribution of temperature at 25 m.

167°30'W due to upwelling around by the bank located in the north ofPrince of Wales.
A northward flow was shown by all kind of surface observations
carried out from the Bering Sea to the Chukchi Sea. Moreover, northward flow in the Bering Strait was already stated by Barnes andThompson (1938) and Uda (1959, 1960), the water belonging this current
is divided into two types of water in the center of Strait (Goodman etal., 1942).
VERTICAL DISTRIBUTION OF TEMPERATURE

It is well-known that the thermocline develops in the summer season
under the influence of heating by the solar radiation in high latitude.
The thermocline existed at the Chukchi Sea and also conspicuous one at
St. 59-63. The steep vertical gradient of temperature was found at
St. 62 and 63, forming most notable thermocline. It is a characteristicfeature that the shallow depth of the thermocline at St. 62, ranged
from 5 to 10 m depth. Off Point Hope, at St. 63 the maximum 11. 7°C
was observed at 7 m depth. Such sub-surface maximums in temperature
were frequently observed at the north of 70°N near the boundary of

OCEANOGRAPHIC INVESTIGATION IN THE CHUKCHI SEA

147

the ice zone (La Fond & Pritchard, 1952).
Bathythermograph data taken from the Chukchi Sea shows that during the summer the thickness of the upper mixing layer was mostly
less than about 15 meters depth. Accordingly, it seems to be lessthan 15 meters approximately in which the influence of heating by
solar radiation attains during the summer season. In addition, theupper mixing layer in northern part of North Pacific, is generally lessthan 20 meters depth (Fleming, 1955).
(m)

0

2.0

4.0

6·0

s.o

10.0

12.0 (C°)

10
20
30
40
50

Fig. 4. Station curves of temperature.

In the observation carried out at St. 63, surface temperature rise toll.0°C or more in midsummer. According to the data obtained by
USSR research vessel, the vertical distribution of salinity at near St.
63, indicates most homogeneous pattern from the surface to the bottom
layer.
As shown in Fig. 4 the gradient of temperatures to vertical direction,
are larger in the eastern part than the west, and the differences between the max. and min. temperature, at St. 66, 67, 69 and 71 wereless than 1.0°C. Especially, the water column at St. 69 was well mixed
from the surface to the bottom and the vertical temperature below 5 m
depth was perfectly homogeneous with 5.5°C. It seems to represent
sinking by the convergence which was formed in between the Siberian
coastal water and northward flow water from the Bering Sea.
The vertical distribution of temperature along the line at 68°20'N isshown in Fig. 5. It indicates that the horizontal distribution of temperature at the surface layer, decreases toward the west and increases toward the east, meanwhile in the bottom layer below 40 m depth, temperatures increase from the east to the west. The cold water with temperature less than 3.5°C at St. 63 locates from 35 m depth to bottom. Warmwater layer at St. 66 was found above 30 m depth. It should be due tothe Bering water mass which flowed into the north from the Bering Strait.
Comparatively the cold water mass locates at St. 65 above 5 m depth withconsiderable thick layer. It may be affected by the southward flow

148

KEIJI NASU

67

(m)

65

66

64

0

63
.................

(St.)
11.0

----10.0

10
20
30

3.0

40

so, ~
4.2 4.6 4·6Fig. 5.

(m)

4.0

Profile of temperature along the latitude of 68°20'N.

39

38

37

36

(St:)

.........~~~~-'-~~~~~-.

or-ir"""~~:--~oe-....,-.._~....,..

10
20
30

40
1.0 2.0 3.0

Fig. 6.

Profile of temperature along the A-line.

from the waters near the North Poles. Hereby, an oceanic frontal
surface is formed and the water mass is divided into two types at theeastern part and the west.
As a rule, the thermocline in the Chukchi Sea is more developed on
the side of Alaskan waters than that on the side of Siberian waters
and its depth, as stated by La Fond Pritchard (1952), increases fromthe east to the west. Basing on the vertical distribution of temperature
the vertical convection in waters is supposed to be more developed to
the west.
Next, the profile of temperature along the A-line, is shown in Fig. 6*.
It shows that the Alaskan warm water mass in the Bering Strait locatesfrom the Diomede Islands to the east area. Moreover, the cold watermass located at the west of the Alaskan warm water mass, has shown* Fig. 6 was drawn by use of data obtained by United States Coast Guard Cooperated with
the Oceanographic Laboratories of the University of Washington in 1939.

OCEANOGRAPHIC INVESTIGATION IN THE CHUKCHI SEA

149

a flow with general northward direction, and turning to the north-west.
This cold water mass indicates subsidence at St. 37. It seems that a
convergence might be formed between the warm water mass at theeast and the cold water mass at the west.
DENSITY

The density of sea water depends upon the temperature and salinity.
Usually, the general distribution of the density is roughly parallel tothe isotherms and isohalines (solenoidal field).
The horizontal distribution of density at the surface is given in Fig.
7, in which the isopycnal of maximum value above 25.00 runs in NNW
direction from the central part of Bering Strait meandering to thecentral part of the Chukchi Sea. It corresponds to the northward flowfrom the Bering Sea.
175°

170°

165°\XI

690 - - . . . . - - . . . . - - . . . . - - - . - - . . . . . . - - _ _ , . . - - - - - - . - - - - . 690

25.00
68°

68°
24.00
\

I
I

I
I

67°

b'

I

I

I

67°

I

I

66°

.a
66°

\JO

J Loo

65oN1~7-5°_ _,__ _.____,__ _.__ _
26·00
65oN
17~0-_ __..__....__......_..__._--:l-65°W
0Fig. 7.

Horizontal distribution of crt at surface.

Lower density waters were found along the Alaskan and the Siberian
coast. Furthermore, along the Alaskan coast the minimum density isfound in Kotzebue Sound (La Fond & Pritchard, 1952). Those lower
density along the coasts seems to be due to the melted ice-water in
addition to the run-off from the land.

150

KEIJI NASU

The isopycnic line of 24.00 in the Alaskan waters is roughly parallelto the coast and 25.00 line is parallel to the west of 24.00 line. In the
Siberian waters the lines of 25.00 and 24.00 are roughly parallel tothe coast. Furthermore, the density varies most rapidly in this region.
This condition is brought about by the convergence formed between the
Siberian coastal waters and the central waters of the Chukchi Sea.
DISSOLVED OXYGEN

The horizontal distribution of dissolved oxygen at the surface is given
in Fig. 8. The concentration of dissolved oxygen at the surface in the
coverage area of observation varied from 9.03 cc/L maximum to 7.17
cc/L. An area with the minimum concentration was found off Point
Hope, which corresponded to the area in the maximum temperature.
The highest concentration was found at near 68°10'N, 173°00'W off
Siberian coast.
Isopleth of 7.50 cc/L extends meandering from the center of Bering
Strait to the north-east. Proceeding eastward from the isopleth of 7.50
cc/L the water of relatively low concentration of dissolved oxygen below
7.50 cc/L extends broadly.
In the western part, 7.5, 8.0 and 8.5 cc/L isoplethes are parallel to eachother, and those isoplethes were concentrated more densely than theeastern area. This phenomenon is considered due to the convergence
between the Siberian water mass and the Alaskan water mass as alreadydenoted in the chapter of temperature. Concerning the horizontal distribution at the surface, the oxygen concentration is low along the Alaskan
waters and high along the Siberian waters.
HYDROGEN-ION CONCENTRATION (pH)The hydrogen-ion concentration was determined by a comparator for
sea water which consists of 2 series of color standard solutions, one
was Cresol Red and the other was Tymol Blue. The horizontal distribution of pH at the surface is shown in Fig. 8. The pH values takenby the observation in the Chukchi Sea are about 8.15 to 8.30. The
distribution of pH roughly corresponds to that of dissolved oxygen.
The waters with relatively lower concentration of pH below 8.20 extends
to the Alaskan waters a like to the area below 7 .50 cc/L in dissolved
oxygen.
Isopleth of 8.20 extendeds from the Bering Sea to the NNW direction,and runs parallel to the west of 8.30 line. The horizontal distributionof pH shows its increase from the east to the west and the closely con-

OCEANOGRAPHIC INVESTIGATION IN THE CHUKCHI SEA
175°
170
690 r---~--.---.---.---...-

151

165°W

........- ........- ......--..---690

s.oo

68°

(8.20>)

67°

67°

66°

66°

65oN ~17~5o~_.__...___.___.__ _1~70_o_..l.-_..l.-_-'-~~--..Jo65oN
165w

Fig. 8. Horizontal distribution of dissolved oxygen and pH at surface.
Solid line-dissolved oxygen.
Broken line and parenthesis-pH.

densed isopleth at about 170°W longitude.
It is well-known that the pH values become high when the photosynthetic activity of marine plants have reduced the content of C0 2
(Sverdrup et al., 1946). The waters of high concentration of pH werealso characterized by higher concentration of dissolved oxygen. Consequently, the productivity in the sea water might be inferred indirectlyby the values of pH. In general, the productivity in the Chukchi Sea
tends to increase in the west and decrease in the east.
WATER COLOR AND TRANSPARENCY

The colors of the sea water were determined by the Forel's scale. Fig.
9 indicates the distribution of water colors. In the investigated area
the minimum value of color of water observed at near 66°30'N, 168°W
and the maximum value (4-5) was found at the north of 67°N, 168°W.
Value of 5 in water color extends widely from the central part of
the Chukchi Sea to the Siberian waters.
Transparency by Secchi disc varies from 7 to 12 m and those isoplethes
is located like a isotherms in the distribution. That is, the isoplethes of

KEIJI NASU

152

67°

67°

66°

66°

65°N .___....__
175°

_,__

_.__

_.__

__.__ _....__,___....._.__....__..... 65°N
165°W
170°

Fig. 9. !so-line of transparency.

7, 8 and 9 m run parallel to the Alaskan coast and to the Siberian coast,
the isoplethes of 7-12 m more or less meander. Lateral intervals of those
isoplethes are roughly similar to the dissolved oxygen and hydrogen-ion
concentration. It is clear in the distribution of the isopleth of transparency that the discontinuous line was formed by the different water
masses along the Siberian coast.
GENERAL OCEANOGRAPHIC CONDITION

Fig. 10 indicates the regions of higher dissolved oxygen and hydrogen-ion concentrations. Furthermore, the boundary line inferred from temperature and salinity, and the current rips observed from the ship werealso shown in Fig. 10. A presumptive current-pattern was indicatedfrom data obtained by this investigation, referring to previous data. It
revealed a cyclonic eddy located at near 67°30'N, l 70°W. At near
66°40'N, l 70°W another relatively conspicuous small cyclonic eddy seems
to be formed due to the northern eddy and the southern coastal waters
along the Siberian coast.

OCEANOGRAPHIC INVESTIGATION IN THE CHUKCHI SEA

153

68°

68'

67°

67°

66°

66°

t
65°N .___
115°_.__.....__

_.._

_..._

__._ _...__-.__._...__.__

110°__. 65°N
165°W

Fig. 10. Summarized oceanographic condition.
Longitudinal line-high value regions of pH. Lateral line-concentrated areaof dissolved oxygen. Arrow-presumptived current. Dotted line-boundary lineof water mass. Undulating line-current rips were observed from the ship.

General oceanographic conditions are as follows :Temperature : higher in the east and lower in the west.
Salinity : higher in the central region, and lower to the east andthe west.
Dissolved oxygen : higher in the west and lower in the east.
Furthermore, marine productivity seems to be higher in the Siberianwaters and low in the Alaskan waters.
SEDIMENT OF THE BOTTOM

Bottom sediments were sampled with a extemporizedly made dredge fromthe sea bottom at about 50 m depth. The dredge also brought up the
specimens of bottom life.
Samples collected at each station are as follows:
St. 59. fine sand-round sand grains round consist of quartz,
felsper and pyroxene without life.

154

KEIJI NASU

St. 63.

gravel-gravels consist of andesite, quartz trachyte andhornstone without life.
St. 69. sandy silt with pebble-Sands consist of quartz and felsper
with many spong spicule.
Furthermore, few diatoms were found in those sediments. The gravels
were sandstones and quartz trachyte.
RADIO-ACTIVITY OF SEA WATER

St. 70-Result of measurement for sample 637 cc, radio-activity was notrecognized at all ( -2.0±1.1 CPM).
DISTRIBUTION OF WHALES

Inspection in the previous reports (Nikulin, 1947; Data obtained by"Yuki-maru" in the Arctic voyage of 1927) showed that larger whalesin the Chukchi Sea were fin, humpback, greenland, right and graywhales.
Fig. 11 shows the locations where all the larger whales were observed
from the "Fumi-maru No. 16 ". Also the Fig. 11 indicated the locations
where gray whales were observed.
The number of the sightings during the season are as follows :Fin whale
1
Right whale2
Gray whale
82
Unknown
1
86
Total
Only one fin whale was observed around 50 sea miles off west of Point
Hope. On Aug. 22, 1927 many fin whales were seen from "Yuki-maru"
in the cyclonic eddy area at about 66°40'N, 170°W. Fin whales wereseen off Cape of Serdzekamen and in the Bering Strait by the observations from the lands. 70 fin whales were seen in October.
Consequently, many fin whales seems to migrate around the Siberianwaters in the Chukchi Sea at least from the early summer to October.
78 gray whales were seen in the convergent area close to the Siberian
coast on August 20. These whales seem to have been fed on the livings concentrated by the convergence.
Many gray whales were observed at the east of the St. Lawrence Island in the Bering Sea. It is well-known that the gray whales migratefrom the Bering Sea to the Arctic Ocean. Migration route of graywhales from the northern part of the North Pacific to the Bering Sea
have been stated (Kellogg, 1929; Gilmore, 1955; Ichihara, 1958). The

OCEANOGRAPHIC INVESTIGATION IN THE CHUKCHI SEA

I''

175°

155

170°W

6 9 0 . - - - - - - - - - . - - - - - - - - - - - -......- - - - - - - - 690

• 00

•

? A ••

68°

68°

67°

66°

65°

•
·~·

'f1)97
4
:I

63

175°

1

64°

63°N

0

Fig. 11. Location of sighted whales.
Black circle-gray whale. White circle-right whale. Black triangle-fin whale. Question mark-unknown. Black square-sighted location on July 28th, 1957. Oblique linesighted location on Aug. 2nd, 1955. (Black square and oblique line indicate the gray whales.)author wishes to keep his opinion that there might be a migration routeof the gray whales at the east of the St. Lawrence Island, too.

156

KEIJI NASU

SUMMARY
The oceanographic and whales sighting survey m the Chukchi Sea
was carried out from Aug. 16 to Aug. 20.
2. The water temperature at the sea surface indicates a trend to
decrease from the east to the west. On the other hand, salinity shows
its increase toward the west and its maximum area located at the central
part of the Chukchi Sea. The salinity decreases from the maximum
area to the the Siberian coast.
3. The cyclonic eddy seems to locate at near of 66°40'N, 170°W.
4. The vertical gradient of water temperatures are greater to the eastand less to the west. The horizontal distribution of temperature at thesurface layer decreases toward the west and increases toward the east,
meanwhile in bottom layer below the 40 m depth, temperature increases
from the east to the west.
5. The maximum values of density were found at the central part of
the Chukchi Sea.
6. The horizontal distribution of dissolved oxygen at the sea surface
shows the lower along the Alaskan waters and the higher along theSiberian waters.
7. The values of pH increased from the east to the west, and the isolines condensed closely at about 170°W longitude.
8. Marine productivity in the Chukchi Sea appears to increase in thewestern part and decrease in the eastern part.
9. During the season number of sighted whales are 1 fin whale, 2 rightwhales, 82 gray whales and 1 unknown whale.
10. The author wishes to keep his opinion that there might be a migration route of the gray whales at the east of the St. Lawrence Island,
too.
1.

REFERENCESBARNES, C. A. and T. G. THOMPSON (1938). Physical and chemical investigations in Bering
Sea and portions of the North Pacific Ocean. Univ. Wash. Publ. Oceanogr., 3 (2): 3579 and Appendix, 1-164.
FLEMING R. H. (1955). Review of the oceanography of the northern Pacific. Intern. North
Pacific Fish. Comm., Bull., no. 2: 1-43.
GILMORE, R. M. (1955). The return of the gray whale. Sci. Amer., 192: 62-7.
GOODMAN, J. R. and J. H. LINCOLN et al. (1942). Physical and chemical investigations:
Bering sea, Bering Strait, Chukchi Sea during the summers of 1937 and 1938. Univ.
Wash. Publ., 3 (4): 8-103.
ICHIHARA, T. (1958). Gray whales observed in the Bering Sea. Sci. Rep. Whales Res. Inst.,
no. 13: 201-5.
KELLOGG, R. (1929). What is known of the migration of some of the whale-bone whale.
Smith1;onian Rep., 2997.

OCEANOGRAPHIC INVESTIGATION IN THE CHUKCHI SEA

157

LaFOND, E. C. and D. W. PRITCHARD (1952). Physical oceanographic investigations in the
Eastern Bering and Chukchi Seas during the Summer of 1947. J. Mar. Res., 11 (1):69-86.
NIKULIN, P. G. (1947). 0 raspredelenii kitoobraznykh v moriakh, omyvaiushikh Chukotskii
poluostrov. lzvestiia TINRO, 22.
RATMANOFF, G. E. (1939). [Chukchi Sea] Soviet North Pole, no. 9.
SVERDRUP, H. u., M. w. JOHNSON and R. H. FLEMING (1946). The Ocean. New York,
Prentice-Hall, Inc., pp.
UDA, M. (1959). Oceanographic seminars. Fish. Res. Bd. Canada.
(1960). Oceanography of the Sub·arctic Pacific (in press). Fish. Res. Bd. Canada.

Ms. Rept. 51: 44-58.
(1960).

On the fluctuation and prediction of ocean temperature in the North Pacific.