Satellite passive microwave studies of the Sea of Okhotsk ice cover and its relation to oceanic processes, 1978–1982

Abstract

This paper describes the use of the Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) satellite data to study the ice cover in the Sea of Okhotsk during the four winters of 1978-1982. The ice concentration estimates obtained from SMMR are used to study two different polynyas: one over the Kashevarova Bank, and the other over the northwest continental shelf. For the Kashevarova polynya this study shows that the polynya, which may be related to the upwelling observed in historic summer cruises, occurs directly over the bank. For the continental shelf, which because of strong offshore winds and cold temperatures is a region of high ice production, the polynya areas are combined with heat flux estimates from weather station data to yield the production rates of ice, salt, and dense shelf water. As a previous study by Kitani (1973) shows, the mixing of this dense shelf water with Pacific water yields a water mass unique to the Okhotsk, which is the layer of cold, low-salinity intermediate water between depths of 150 and 800 m. From our calculations, we estimate that the dense shelf water is produced at an annual rate of about 0.5 Sv, and that the intermediate water is produced at a rate of 1-2 Sv, which yields a renewal time for this layer of 10-40 years. 1. the Kamchatka Peninsula to the east, the Asian continent to the north, and Sakhalin Island to the west (Figure 1). For this study, the most important topographic features of the Okhotsk are the broad northwest continental shelf between Magadan and Shantarskiy Bay, and the topographic rise northeast of Sakhalin Island called the Kashevarova Bank (55ø5øN, 145øE). Although the Okhoisk is geographically located at temperate latitudes, it has many characteristics of a polar ocean' severe winters with cold temperatures and high winds, mild but short summers, large seasonal variations in atmospheric and water temperatures, and a subarctic water column structure. The Okhotsk also has a seasonal ice cover present from December through April with a thickness of the order of 1 m and an areal coverage comparable to that of the Bering Sea [Tabata, 1958' Parkinson et al., 1987]. The Okhotsk is connected to the Sea of Japan by two narrow, shallow straits' the Soya Strait south of Sakhalin, with a sill depth of 40 m, and the Tartar Strait between Sakhalin and the mainland, with a depth of 10 m [Favorite et al., 1976]. These shallow depths greatly restrict the interaction of the Okhotsk with the Sea of Japan. To the south, the Kuril island chain has two deep straits which allow for exchange of the Okhotsk water with the Pacific. These straits are the Bussol' Strait with a maximum depth of 2300 m, and the Kruzenshterna Strait with a 1900-m depth. The basic circulation in the Okhotsk consists of a large cyclonic gyre, which consists of the surface and subsurface northward flow of Pacific water through the Kruzenshterna Strait then along the Kamchatka Peninsula [Moroshkin, 1966' Leonov, 1960]. The flow next circulates around the northern x Now at International Ice Patrol, Av...

Evidence of change in the sea of okhotsk: Implications for the north pacific

“…Two potential source regions of NPIW have been proposed: the Sea of Okhotsk outflow (Wust, 1930;Kitani, 1973;Alfultis and Martin, 1987;Talley, 1991;Talley and Nagata, 1995;Yasuda, 1997); and the Gulf of Alaska (Van Scoy et al, 1991;You et al, 2000). The latter has received less attention in recent years; as Van Scoy et al (1991) admitted, waters of 26.8 σ θ have never been observed at the surface in the Alaskan Gyre.…”

“…The Kashevarov Bank is a site of intense heat loss and hence dense water formation (Alfultis and Martin, 1987) related to the strong upwelling and vertical mixing discussed by Suzuki and Kanari (1986). With much dispute as to whether dense water is produced in sufficient quantities to form NPIW, Alfutis and Martin (1987) focused on estimating the magnitude of this OIW production through an estimation of the production of dense shelf water.…”

Surface Heat Budget of the Sea of Okhotsk during 1987-2001 and the Role of Sea Ice on it

“…Therefore, sea ice transports negative heat and negative salt from north to south. Salt rejection due to active sea ice formation in the polynyas over the northern and northwest shelf produces Dense Shelf Water, which is regarded as a ventilation origin of North Pacific Intermediate Water (NPIW) (Alfultis and Martin 1987).…”

“…It showed that the heat fluxes over open water area are two orders of magnitude greater than those over the sea ice. For the Okhotsk coastal polynyas, Alfultis and Martin (1987) and Martin et al (1998) calculated the net surface heat flux by the bulk method to investigate ice and brine production in the polynyas. All these heat flux estimates are confined to a limited region; the surface heat flux for the entire Okhotsk Sea has not been estimated on the basis of observed data.…”

Community compositions of Bacteria and Archaea in the Sea of Okhotsk during summer

“…Although the Sea is geographically located at a temperate latitude, it has many characteristics of a polar ocean, namely, large seasonal variation in water temperatures (~14°C) and large amounts of sea ice along the Siberian coast over the northwestern continental shelf of the east coast of Sakhalin Island every winter (Alfultis & Martin 1987). The Sea of Ohkotsk is recognized as the most productive marine basin amongst the world's oceans (Sorokin & Sorokin 1999).…”