Changes of Zhe-Min Coastal Water in the Taiwan Strait in Winter during Past Thirty Years

The cold, fresh and eutrophic Zhe-Min Coastal Water (ZMCW) is the main current on the west side of the Taiwan Strait (TWS) through the whole year except for summer. It plays an important role on the circulation, biogeochemical processes and marine ecosystem of TWS. The ZMCW in the TWS have the most extensive impact area and the strongest intensity in winter. In this study we analyzed the long term characteristics of ZMCW base on the merged satellite-derived sea surface temperature (SST) data from 1985, combining with wind, ocean current, sea surface height and runoff data. The areal index (ArI) and intensity index (InI) of ZMCW were established rely on the temperature threshold method based on in situ measurement. The statistics showed the ArI and InI had a tendency to increase during the period from 1981-2016. The enhancement was most significant after year 2000. The average of the ZMCW impact area and intensity during the year 2010-2016 increased by 29.3% and 63% than that of 2001-2009, respectively. The spatial distribution of ZMCW during 2001-2016 extended more southward and eastward than that of 1985-2000. Preliminary analysis indicated that these changes of ZMCW are mainly attributed to the increasing trend of northeast wind. Furthermore, the increase in the sea surface height difference between the East China Sea and South China Sea after 2000 may lead to the significantly enhanced ZMCW in recent years.