SURFACE WATER CONDITION IN THE ANTARCTIC
WHALING PACIFIC AREA IN 1956-57
KEIJI NASU
INTRODUCTION

In this paper the surface water conditions in the Antarctic whalinggrounds are discussed by use of the oceanographical data obtained by ourinvestigations 1956-57, on the board of whaling factory ship "Nisshinmaru" and the whale marking research boat "Fumi-maru No. 17" belong to the Taiyo Fisheries Co., Ltd.
Our observation area is mainly covered by the region within the foremore whaling sanctuary area, from 70°W to 150°W. The oceanographical materials treated in this paper are the terms of surface temperatureand salinity of sea water. The observations concerning these materials
were made at interval of 4 hours on the board of "Nisshin-maru"
and on the board of "Fumi-maru No. 17" at interval of one hour,
during the whale marking research before the opening baleen whaling.
WHALING GROUNDS IN THE FOREMORE SANCTUARY AREA

Considering from twice catch operations carried out by the JapaneseWhaling Expeditions, the whaling grounds within the foremore sanctuary area can be roughly separated into three parts.
Namely, these whaling grounds are located along the meridians of90°, 120° and 150°W. The operations in the ground along the 90°W
were mainly carried out in the beginning season (January) and afterwards
shifted towards the west sea areas with the pass of the whaling season.
Moreover, the latitudinal area of these whaling grounds corresponds tothe domain from about 60°8 to 71 °S.
The positions of northern-most and southern-most parts of thesegrounds exist near the 140°W. And, generally speaking, as for thelatitudinal width of the whaling grounds, it appears to become narrowfrom west towards east.
HO RIZO NT AL DISTRIBUTION OF SURF ACE TEMPERATURE
AND SALINITY

December.

The -1.5°C-isotherm is situated in the east of the Peter I137

138

K. NASU

Island, in the neighbourhood of 68°8, 83°W. And, in this region it isextended in a tongue shape towards the NE direction. In the vicinityof the tongue area, the temperature changes abruptly.

Fig. 1.

The horizontal distribution of temperature at surface.

Fig. 2.

The horizontal distribution of salinity at surface.

December 1956.

December 1956.

The 33.50%0-isohaline is distributed in the same pattern as the temperature isoline, and in this region the low temperature and salinity
water mass, which is formed by the melting ice and moves northward,
is apparently found. The salinity seems to reduce gradually with thepass of month, as already described by 8ugiura (1949). The sea waterin this region is well known as the Antarctic surface water (Midttunand Natvig, 1957).
At the position of 66°-30'8, 73°-00'W, the tongue shape distributionof the high temperature and salinity water mass (more than 0.5°C and34.00%0) is projected towards the west. Near 74°W, the meandering
discontinuous lines of temperature and salinity are found. At the position of 64°8, 83°W, the water mass having the high temperature andsalinity more than 1.0°C and 33.90%0 is situated towards the south-west.

SURFACE WATER CONDITION IN THE ANTARCTIC WHALING PACIFIC AREA 139

And, in the region of south-west direction of the above water mass
(about 68°8, 93°W), there exists a tongue shape region which extends
towards the southern direction.

w'Pack-ice

1lTl7lrFig. 3. The horizontal distribution of temperature at surface.

!77lJn-January 1957.

wPack-ice
I 0Fig. 4.

/10The horizontal distribution of salinity at surface.

January 1957.

In the vicinity of the about 65°8, 110°W, the low temperature andsalinity water mass which are formed by -0.5°C and 33.50%0 run
northerly in a tongue shape. In the western part of the above tongue
shape region, the comparative high temperature and salinity water mass
(more than -0.2°C and 33.70%0) is projected southerly. The isotherm
and isohaline of this region are laterally meandered and it seems that
their patterns form the cyclonic.
January. Observation area covered from about 105°W to 130°W. The
surface temperature in this area varies from 0.5°C to -0.9°C. The
distribution of pack-ice at January is extended towards the east fromthe vicinity of the position 66°, ll 7°W and it is directed southerly
very sharp from the position of 66°8 and 110°W. To the east area ofthe pack-ice, the tongue shape of the isolines of relative high tempera-K. NASU

140

ture and salinity with values more than 0.0°C and 33.60%0 is penetrated
towards the south-west. To the west side of the south-westerly tongue
region, the low temperature and salinity water mass is projected towards the north-east. This fact would have been probably caused by
the condition of distribution of pack-ice. In the sea region between thenorthern and southern currents evaluated by referring the isoline map
are formed the intricate sea conditions, and the distribution of temperature in this area varies abruptly.

-0.4~ Pack-ice/50Fig. 5.

/40'W

The horizontal distribution of temperature at surface.

Fig. 6.

The horizontal distribution of salinity at surface.

February 1957.

February 1957.

The condition of pack-ice at the western part of the ll 7°W is notclear, but it will be evaluated that the pack-ice is distributed towards
southern direction from about 117°W.
At the vicinity of 117°W, the high temperature and salinity watermass is found, and at the west part of it, near the 128°W, the considerable emphatic tongue shape running toward the south-west direction
is recognized.
February. Observation area made in this month is covered from 160°W
to 120°W. And, the minimum temperature in this region was -l.4°C

SURFACE WATER CONDITION IN THE ANTARCTIC WHALING PACIFIC AREA 141

in the edge of pack-ice and also there exists the tongue-shaped low
temperature zone extending towards the east direction along the packice zone. Moreover, the low isohaline of 33.30%0 runs in the same pattern as the low isotherm along the pack-ice line. In the vicinity of thepack-ice zone the low temperature and salinity water mass is found,and the hydrographical conditions of water mass vary extremely. This
fact is clearly influenced by the melting of ice, as described by Sverdrup
et al (1946), and it is assumed that before the occurrence of its melting,the distribution of ice was extended towards the east.
On the other hand, the high temperature and salinity water mass isextended towards the west part, and in this part there exists themeandering convergence. Generally, the temperature and salinity inDecember, January, and February are distributed to the tendency tohave high value in the east and low in the west. The isoplethes oftemperature and salinity are analogous each other.
SEA CONDITION IN THE VICINITY OF THE PACK-ICE

It is clear from the facts already stated that the water temperatureand salinity are low in the vicinity of the pack-ice. But we cannot•

Salinity ('/,,)

Temperature.

Salinity

(oC)

.72
33.70
.68
.66

1.0
0.8.64
.62
33.60

0.6
0.4
0.2

.58
.56
.54

0o.o

0-0.2

.52
33.50

lO

2030

4050

Sea mile

Distance from the pack-iceFig. 7.

Temperature and salinity in the vicinity of pack-ice.

assert the generality of this character. Because, the above result did
not be deducted from an average treatment of the data obtained by manyobservations. But, it is recognized that the salinity becomes abruptly
lower within the domain of distance 30 sea miles from the pack-ice
zone. Besides, Tsuchida (1952) has pointed out that the distribution ofsalinity changes suddenly within the domain of distance 100 sea miles
from the pack-ice.
Referring from Fig. 7, it seems that water temperature is ascent withapproaching to the pack-ice and is descent at the nearest vicinity of

142

K. NASUthe pack-ice. But, we will consider that this phenomenon is unreasonable under our physical analysis. Because, in our treatment concerning
the distribution of water temperature, we did not take into accountthe effect of the time dependent deviation of water temperature causedby the variation of the various kinds of meteorological factors with thephase shift of the time of observation in the respective positions.
RELATION BETWEEN THE SURFACE WATER CONDITION
AND THE WHALING GROUNDSIn January, the main whaling grounds are situated near the regions of65°S-115°W and 67°S-107°W, and in the neighbourhood of these tworegions the southerly warm currents are found.
In February, the area of whaling grounds are narrower than that inJanuary, and the center of ground area in this month are located near
the position of 67°S-145°W, in where the relative high temperature andsalinity water mass are projected towards the west. The most of whale
caught in this area are fin whales, and the blue whales which are very
few in the same ground are caught in the relatively lower temperature
region, especially in the region near the pack-ice water.
It will be considered that the center of whaling grounds were situatedin the tops of the tongue shape of isotherms and isohalines, as alreadyreported by Shimomura (1950). Generally, it can be assumed that thesoutherly warm currents play a very important role for the formationof the Antarctic whaling grounds, especially baleen whale's ground.
ACKNOWLEDGEMENT

The author is obliged to Dr. Michitake Uda, Prof. of the Tokyo University of Fisheries, and Mr. Takahisa Nemoto, a member of the Whales
Research Institute, for their instruction and helpful suggestions. Dr.
Yasukazu Saito and Mr. Makoto Ishino, the Tokyo University of Fisheries,
read this manuscript and gave him the valuable suggestions.
Last of all, the author would like to express his hearty thanks toMr. Yuji Tobita and Mr. Kazuo Haga, member of Fisheries Agency who
co-operated this research on the board of " Nisshin-maru ".
SUMMARY

1. Generally, the water temperature and salinity at the former
sanctuary area have a tendency to be high in the east and low in thewest.

SURFACE WATER CONDITION IN THE ANTARCTIC WHALING PACIFIC AREA 143

2. The salinity around the pack-ice have varied in the vicinity of 30
sea miles apart from the pack-ice.
3. It can be assumed that the southerly warm currents play a very
important role for the Antarctic baleen whale's ground.

REFERENCES
MIDTTUN, L. and NATVIG, J. (1957). Pacific Antarctic Waters Publikasjon Nr. 20. Fra
Kommandcfir Chr. Christensens Hvalfangstmuseum 1 Sandefjord. Sci. Res. "Brategg"Exp., 1947-48, No. 3.
SHIMOMURA, T. (1947). On the Sea-condition and whaling of the Antarctic Sea. J. Oceanogr. Soc. Japan, 5 (2-4). (In Japanese).
SUGIURA, J. (1949). Report on Sea and Weather Observation on Antarctic Whaling Ground(1947-48) Oceanogr. Mag. C. M. 0. Vol. 1. No. 1.
SVERDRUP, H. N., JOHNSON, M. w., and FLEMING, R. H. (1946). The Ocean. New York,Prentice.Hall, p. 609.
TSUCHIDA, T. (1952). On the oceanographical conditions of the Antarctic region in 195152. Oceanogr. Rep. C. M. 0. 2 (4).