Abstract
One of the major sources of iron supply to the Okhotsk Sea and the Oyashio region, which both have high biological productivity, is thought to be regions of the East Sakhalin Current and its upstream, originating from the Amur River. This study suggests that the Soya Warm Current (SWC) region could also be a possible source of iron via resuspension of bottom sediments. We derived the volume backscatter strength from acoustic Doppler current profilers (ADCP) data that had previously been collected in the SWC region. The backscatter strength data indicate that prominent sediment resuspension occurs in both the upstream and downstream regions of the SWC when the bottom current exceeding 0.5 m/s continues to some extent. In the upstream region, strong current events that induced the sediment resuspension occurred through the SWC intensification caused by the increase in sea-level difference across the Soya Strait excited by the southerly winds. Such events frequently occur from September to December, because of frequent passages of cyclone. By contrast, in the downstream region, sediment resuspension occurred due to the strong northerly winds via the current increase caused by the coastal trapped waves over the shelf in winter. The sediment resuspension in the downstream region was also supported by direct observations of high turbidity near the bottom. High iron concentrations in the coastal Oyashio water possibly originate from the SWC water. The occurrence of the resuspension during the sea ice season suggests the potential local incorporation of sediment into sea ice.