Observed inter-annual variability of volume transport in the transect of 120°E in the northeast of South China Sea

Using hydrographic data along the 120°E section in each September from 2005 to 2009, 2011 and 2013 with the geostrophic calculation and normal mode solution, we reveal the vertical characteristics and interannual variation of the velocity fields in the northeastern South China Sea (SCS). The velocity fields in 2005, 2006, 2007 and 2013 change direction with depth and present a baroclinic structure, which are dominated by the barotropic and the first baroclinic modes according to the normal mode analysis. Differently, the velocity fields have uniform vertical structures in 2008, 2009 and 2011, which mainly result from the barotropic mode contributions. The volume transport along section 120°E as depth can be classified into three groups: westward transport in all the depth (say 2005, 2007 and 2011), westward transport in the upper layer and eastward transport in the deeper layer (say 2008 and 2013), and eastward transport in the upper layer and westward in the lower layer (say 2006 and 2009). The net volume transport along the section 120°E presents significant interannual variability. The maximal westward transport is -11.2Sv in 2005, whereas the maximal eastward transport is 9.1Sv in 2013. The minimal transport occurs in 2009 with the value of only -1.2Sv.