The Quantitative Analysis of Water Mass during Winter on the East China Sea Shelf Using an Extended OMP Analysis

The distribution and quantification of water masses on the East China Sea (ECS) shelf is important for identifying and understanding historical climate-driven changes in ocean properties and circulation in the region. We applied an extended Optimum Multiparameter (eOMP) analysis to quantify the relative contribution of water masses using wintertime temperature, salinity, nitrate (NO3-), phosphate (PO43-), and silicate (SiO32-) measurements from a five-cruises dataset spanning from 2013 to 2018. Average ratios (NO3-:PO43-:SiO32- = 47:1:35) derived from field observations were used to correct the equations referring to the chemical parameters. Our analysis indicated that wintertime seawater on the ECS shelf consisted mainly of Changjiang Dilute Water (CDW), Yellow Sea Coastal Water (YSCW), Taiwan Warm Current Water (TWCW), and East China Sea Shelf Water (ECSSW). The results from the eOMP analysis demonstrated the natural boundaries of four water masses during winter. The interannual variability of water masses showed that the CDW distribution was relatively stable in winter, and there was strong anticorrelation between the YSCW and TWCW extents, suggesting that these two water masses mostly displace each other in the north-south direction.