Drivers of Subsurface Low Potential Vorticity Water Intrusion Into the South China Sea During 2014–2016

Abstract Subsurface Low Potential Vorticity Water (SLPVW), which originates from the North Pacific Subtropical Mode Water (STMW), plays a key role in shaping and memorizing climate variability in the North Pacific. Few studies have focused on the SLPVW intruding into the South China Sea (SCS) and its subsequent influences. By combining observed and numerical model data sets, we document a pronounced and persistent intrusion of the SLPVW into the SCS during the 2014–2016 period. This intrusion was driven by strengthening the STMW subduction rate and the Luzon Strait transport (LST). Notably, the STMW subduction rate began to increase approximately 5 years prior to the 2014–2016 period, coinciding with an already enhanced LST, which together facilitated the strong SLPVW intruding into the SCS. Under the effect of the SLPVW intrusion, a subsurface intensified anticyclonic eddy was thus generated in the upper 500 m layer. The most pronounced hydrographic changes appeared in the subsurface layer (100–300 m), with temperature and salinity anomalies reaching up to 1.77 and 0.14, respectively. Maximum zonal and meridional velocity anomalies in the subsurface layer increased by as much as 30 and 25 cm s −1 , representing a substantial enhancement relative to climatological mean currents. These findings offer new insights into the mechanisms driving subsurface hydrological variability in the northern SCS.