| Research Abstract |
Purposes
The Sea of Okhotsk(OK), which is located between the Sibeiian continent and the North Pacific, is covered by ice from November through June, and is one of the southernmost ice-covered oceans in the Northern Hemisphere. The interannual variability of the sea-ice in the OK is large and sea-ice coverage has abniptly decreased since the end of the 1980's. Also, the sea-ice influences large scale climate such as the development of the Aleutian low and the formation of the Noiih Pacific intermediate waters 8-10. In analogy with the Arctic Ocean, sea-ice in the OK has been believed to be influenced by the ground hydrological processes. Previous studies suggest the existance of a highly siralilied, low-salinity surface layer in the OK, which suppresses deep convection and promotes freezing. It has also been speculated that the low-salinity layer is mainly due to the inflow of the fresh water from the Amur River. Although previous studies attempted to find evidence of the river-water in
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fluence on the sea-ice using data analyses, the lack of reliable interannual data for sea-ice precluded direct comparison between the ice-data and the discharge-data Because the period of reliable satellite-based ice-data has become long enough to analyze the inteninnual variability, we are now able to directly compare the two. The purpose of our study is to collect the Amur discharge data and to quantify the effects of the Amur discharge on the sea-ice on interannual and longer time scales
Results
The impacts of ground hydrology on the high-latitude oceans, such as melting glaciers and discharge from rivers in the oceans, can affect global climate by mediating the flow of low-density, fresh water inflow that strengthens the ocean's stratification, suppresses the thermohaline circulation and also promotes sea-ice formation. Ourtime series analysis based on sea-ice and river-discharge data indicates that the effect of this fresh water on the sea-ice in the Sea of Okhotsk, into which the second largest Siberian River, the Amur, discharges, is relatively unimportant Interannual variations in the ice extent are negatively correlated with the amount of discharge. We find evidence that the inflow of wanner river water tends to the raise of the sea surface temperature, and that it suppresses ice formation in the following winter. These findings imply that sensible heat transported by large rivers in high latitudes should be reconsidered in studying global climate change. Less
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