Zooplankton indication of the Yellow Sea Warm Current in winter

Abstract

In winter, strong north wind drives southward flow at the surface along both Korean and Chinese coasts, which is compensated by a northward flow along the Yellow Sea Trough and known as the Yellow Sea Warm Current (YSWC). It advects warmer and saltier water from the East China Sea into the Southern Yellow Sea and changes the zooplankton community structure greatly in winter. And the distribution of zooplankton can also be used as bioindication of the YSWC. To see the warm water species distribution in related to the YSWC, plankton samples were collected in November 2001 in the Southern Yellow Sea after the onset of the winter monsoon. 71 zooplankton species were identified, among which 39 species were tropical, accounting for 54.9%, much more than that found in summer. Many of them were typical for Kuroshio water, eg. Eucalanus subtenuis, Rhincalanus cornutus, Pareuchaeta russelli,Lucicutia flavicornis,and Euphausia diomedeae etc. 26 species were warmtemperate accounting for 36.6% and 6 temperate 8.5%. However the zooplankton community was still dominated by temperate and warmtemperate species. Calanus sinicus was the overwhelming dominant one (dominance=0.4331). The distribution pattern of the warm water species shows clearly that the YSWC flows beneath the surface northwards into the Yellow Sea along the Yellow Sea trough. The north limit to what the YSWC can penetrate was about 35-36°N judging from the horizontal distribution of the warm water species. The vertical profiles of the warm water species show that the intrusion of the warm water took place mainly in the middle layer. In summer warm water species can also be found in the Yellow Sea but the diversity was much less than that in winter and short of typical species for Kuroshio water. The appearance of warm water species in summer in the Yellow Sea would be a consequence of the expansion of their distribution area in response to the warm up of water temperature rather than the transportation by warm current. 