A mesoscale eddy-induced biological structure observed from satellite ocean color observations in the East Sea

Abstract

A mesoscale anticyclonic eddy influencing spatial and temporal aspects of biological variability was detected from satellite ocean color observations in the East Sea, typical of Case-1 waters. This eddy formed in spring and summer apparently altered the optical properties of water column by enhancing chlorophyll concentrations from 0.5 to 8 mg/m3. Enhanced chlorophyll concentrations may be attributed to high levels of nutrients transported from coastal regions and from deep waters by the action of eddy. Satellite measurements of chlorophyll were supplemented with AVHRR sea surface temperature data and with ship-based observations using CTD and other optical sensors to better understand the characteristics of the anticyclonic eddy feature in the East Sea. Horizontal distribution of potential temperature (&#61553;) and salinity (S) of water off the Southeast coast exhibited cold and low saline surface water (&#61553;<19&#61616;C; S<32.4) and warm and high saline subsurface water (&#61553;>12&#61616;C; S>34.4) at 75dBar, corroborating the northeastward intrusion of Tsushima Warm Current (TWC) along the Tsushima Strait and the northward branch of East Korean Warm Current (EKWC) along the Korean east coast. The EKWC separated from the coast at about 37-38&#61616; N and formed a mesoscale anticyclonic eddy feature off the Korean east coast during spring and summer. The process of such mesoscale anticyclonic eddy feature might have produced interior upwelling that could have shoaled and steepened the nutricline, enhancing phytoplankton population by advection or diffusion of nutrients in the vicinity of Ulleungdo in the East Sea. By late summer and fall when antheropogenically-influenced coastal water supported high chlorophyll biomass, the northward EKWC instead of influencing the anticyclonic eddy circulation would entrain chlorophyll from an adjacent eddy/upwelling and coastal areas, forming a conveyer-belt transport process to inject coastal biota into the open-ocean r