Dense water production on the northern Okhotsk shelves: Comparison of ship‐based spring‐summer observations for 1996 and 1997 with satellite observations

Abstract

For the northern Okhotsk Sea polynyas, five Russian CTD surveys taken during 1995 to 1997 are used to examine the evolution of the polynya dense water. The surveys show that consistent with other investigations, the largest potential densities are 26.99 σθ, and the densest water occurs in Sakhalin and Shelikhov Bays. The surveys also suggest that the Shelikhov water drains directly into the deep Okhotsk, while on the northern shelves, gravity currents transport the dense water west to Sakhalin Bay. For comparison, determination of the polynya sizes and ice production from satellite passive microwave and meteorological observations shows that polynyas occur on the northwest shelf (NWS) between Ayan and Okhotsk City, on the northern shelf between Okhotsk City and Magadan, and in Shelikhov Bay. In contrast, the observations show that Sakhalin Bay is a region of land fast ice with no polynyas, so that the dense water observed here cannot form locally. For all polynyas the satellite observations show that the NWS contributes 60 to 70% of the total ice production, and due to the warmer 1997 air temperatures, the 1996 production is about 1.5 times the 1997 value. An estimate of the ice production from the surveys shows a similar regional distribution and enhancement of the 1996 production, with the satellite and ship estimates in agreement within their error bars. Finally, analysis of the dense water outflow shows that the upper Okhotsk Sea Mode Water has a renewal time of about 4 years; the lower part, about 14 years.