Impact of Climate Variability of the Western Tropical Pacific on Maximum Salinity Water in the South China Sea
Salinity observations in the Vietnamese upwelling area in June 2016 indicated a significant increase in the salinity of the maximum salinity water (MSW). The source of MSW inflow into the South China Sea (SCS) is a mixture of the Western North Pacific Central Water and the North Pacific Equatorial Water. Although the East Asian winter monsoon is correlated with both the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), the mean salinity of MSW is only spuriously lag correlated to the PDO, but highly correlated to all tropical climate modes (except El Niño Modoki) with a time lag up to 7 months. Composite analyses indicate that the modulation of ENSO by a PDO in a positive phase results in optimal inflow conditions. A comparison of two post-El Niño years with different PDO polarity (negative in 2003 and positive in 2016) shows that the dominant driver is the variability in outgoing long-wave radiation (OLR) and in zonal wind in the tropics. In 2003, enhanced convective activity over the West Pacific warm pool resulted in a cyclonic circulation. In 2016, convective activity was weak and an anticyclonic circulation was intensified, which transported the saltier North Pacific Equatorial Water into the SCS. This observed increase in the salinity of MSW requires a modification of the previous definitions of characteristic water masses, which is presented here. The question of whether or not the increase in MSW salinity is a transient phenomenon cannot be answered. It might be possible that the increase in salinity is related to global warming.
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- Ocean Dynamics