Departmental Bulletin Paper 日本海深層循環における底層水の形成
Formation of the Bottom Water in the Abyssal Circulation in the Japan Sea

荘司, 堅也  ,  磯田, 豊  ,  久万, 健志  ,  荒巻, 能史

65 ( 1 )  , pp.17 - 29 , 2015-03-16 , 北海道大学大学院水産科学研究院
The abyssal waters in the Japan Sea vertically consist of the homogeneous Bottom Water (BW) and the weak-stratified Deep Water (DW). The formation of BW was inferred based on the spatial difference of their recent warming trends in potential temperature from 2000 to 2007 and the snapshot hydrographic observation in 2007 around a benthic front on the shallower sill region between the Yamato Basin (YB) and the Japan Basin (JB). It is found that there is no significant change in the thickness of BW, but both BW and DW showed clear warming trends. Geothermal heating from the seabed with order of 102 mW m-2 is plausible candidate having potential to cause the vertical mixing of BW and its reasonable warming trend with order of 10-3 °C yr-1. Considering upward advection of such heating from BW, the warming trends of DW at YB and JB are respectively examined using the one-dimensional advection-diffusive equation. The results suggest the existence of horizontal abyssal density current between both basins, i.e., on the sill, which was consistent with the snapshot spatial distributions of salinity and dissolved oxygen. If this local abyssal circulation may be continuously generated by the horizontal density gradient between both basins, the thickness of warming and vertical mixed BW will be always restricted by the sill depth.

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