OHSHIMA KAY I

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Research Institute for Humanity and Nature Repository

CIRCULATION AND HEAT/SALT TRANSPORT IN THE SEA OF OKHOTSK AND ITS RELATION TO SEA ICE 0HSHIMAKAYI Institute of Low temperature Science, Hokkaido Uniνersity INTRODUCTION The Sea of Okhotsk is the southernmost seasonal ice zone in the Northern Hemisphere with large interannual variations of sea ice extent, and thus it can be considered as a sensitive indicator of climate change. North Pacific Intermediate Water σ~IW) is ventilated mainly in and around the Okhotsk Sea (Talley, 1991 ).In other words, the Okhotsk Sea can be regarded as the only site that the atmosphere can directly exchange the heat and material (including C02) with the intermediate water in the North Pacific. Thus, water-mass formation has been studied in several papers (e.g., Kitani, 1973). However, the circulation of this sea had not yet been well understood due to the lack of direct cuηent measurements. The Okhotsk circulation was presented only schematically, based on water岨massdistribution, ship and ice drift, and sporadic short-term current measurement (Moroshkin, 1966; Luchin, 1998). According to their schematic figures, a cyclonic gyre dominates the northern half of the Okhotsk with a southward boundary cu汀entalong Sakhalin Island, historically called the East Sakhalin Current (hereafter ESC). The Joint Japanese田Russian-U.S.Study of the Sea of Okhotsk, carried out during 1998-2001, has considerably revealed the oceanography of the Okhotsk Sea : itscirculation, water exchange with North Pacific, dense shelf water formation, heat/salt budget, the role of sea ice etc. In this paper, these results are summarized, together with heat flux calculation. 1. CmcULATION IN THE SEA OF OKHOTSK Under the Joint project, intensive direct current observations have been made during 1998-2001 in this sea both企omLagrangian and Eulerian measurements. Figure 1 shows the spatial distribution of the mean surface flow derived from 20 surface drifters (Ohshima et al., 2002). The figure clearly shows that the southward East Sakhalin Current is a steady feature with typical speeds of 0.2・0.3m s-1 (the mean velocities exceed the e町orellipses significantly). This figure also shows that a part of this southward current continues as far as the southern tip of Sakhalin Island while a part of the current turns to the east around Terpeniya Bay ( 48°N) flowing eastward as far as Bussol’Strait. This eastward current together with the southward East Sakhalin Current constitutes a part of the cyclonic gyre in the Okhotsk Sea. The fact that al the drifters in the western part move southward implies the compensated northward flow in the eastern part of the Okhotsk Sea. 23 

Circulation and Heat/Salt Transpo吋inthe Sea of Okhotsk and Its Relation to Sea Ice

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Circulation and Heat/Salt Transpo吋inthe Sea of Okhotsk and Its Relation to Sea Ice

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