Dense Water Formation in the Okhotsk Sea

National Science Foundation Grant OCE-9811958

9/15/1998 – 8/31/2003

Lynne D. Talley and Daniel L. Rudnick

Scripps Institution of Oceanography, UCSD, La Jolla, CA 92093-0230 USA

Project Summary (from 1998 proposal):

The principal ventilation site for intermediate density waters of the North Pacific is the Okhotsk Sea. The Okhotsk Sea and North Pacific exchange waters through the Kuril Islands, with the two deepest passages being Bussol' and Kruzenshtern Straits. Within the Okhotsk, surface waters are transformed to denser intermediate waters mainly through the process of brine rejection during sea ice formation. The extensive coastal polynya over the broad northern/northwestern shelf is a major ice production area. These dense shelf waters ventilate the intermediate depths of the Okhotsk Sea. The transformed waters then flow out of the Okhotsk Sea where they join the Oyashio and are advected onward into the North Pacific. In addition to providing quantitative understanding of the downward limb of the overturning cell in the North Pacific, the proposed experiment will provide basic insights into coastal polynya processes in a region which is logistically accessible (and previously politically inaccessible), with good satellite and meteorological coverage.

The proposed field project consists of:

(1) an examination of formation of shelf water under sea ice in the northwestern coastal polynya through one winter, using moored temperature/salinity/pressure/ADCP measurements of water properties

and

(2) hydrographic (CTD/rosette) surveys of the northern Okhotsk Sea and East Sakhalin Current (outflow from shelves) upon deployment and recovery of the moorings.

Analyses of historical data, including hydrographic data, sea ice records, and meteorological data, will provide a context for the experiment and an estimate of the interannual variability in intermediate water production and properties. This work would be joint with S. Martin, with our principal contribution being analysis of heretofore unavailable Russian data. The proposed in situ studies are complementary to a proposal from S. Martin to study the air-sea fluxes and ice cover in the Okhotsk Sea during the same period using satellite and NCEP information. It is also complementary to a modeling study of the Okhotsk and Bering Sea polynyas being proposed to ONR by G. Gawarkiewicz and D. Chapman. Taken together, these projects will provide an excellent first description of the intermediate water formation process, and a useful comparison point for the model. In particular, along-shore advection and large tidal amplitudes may be important in the Okhotsk Sea northwest shelf polynya and remain to be incorporated in the Gawarkiewicz/Chapman model.

A funded joint U.S.-Japan mooring project in Bussol' Strait (major exchange location between the Okhotsk Sea and North Pacific) during the same period will provide concurrent outflow information, as the newly ventilated and mixed waters move on into the North Pacific.

Strong collaboration with Russian and Japanese groups working in the Okhotsk and Kuril regions is a major aspect of this project.