The production of ice and dense shelf water in the Okhotsk Sea polynyas

Abstract

This paper examines the ice and dense water production in the Okhotsk Sea coastal polynyas for the 1990-1995 winters. The dominant polynyas occur on the northwest and northern shelves and in Shelikhov Bay. We use an algorithm developed for the special sensor microwave/imager (SSM/I) to derive for each polynya the area and composition of thin ice and open water and a heat flux algorithm to derive the ice and brine production. Historic oceanographic observations show that the northwest shelf is the only North Pacific region where the σν = 26.8 potential density surface outcrops to the surface and is also that part of the Okhotsk shelf where the densest water is observed to occur. In support of these observations, we find that the northwest shelf polynya is the dominant ice and brine producer, contributing on average about 55% of the total production. Shelikhov Bay is the second largest producer with about 25% of the total; this region has been previously neglected by both oceanographic and remote sensing studies. Using a combination of two dense water production models, we find that the 6 year average dense water production lies between 0.2-0.4 Sv. The ice and brine production for the dominant northwest shelf vary interannu-ally by a factor of 3, while the production from all the northern polynyas varies by factor of 2. The source of the variability for the northwest shelf comes from the fact that the southwest-to-northeast trend of the coastline and the mean winter geostrophic wind velocities are roughly parallel, which means that small variations in the wind direction yield large changes in the ice production.