Spreading of Antarctic Intermediate Water in the Philippine Sea

The Antarctic Intermediate Water (AAIW) is carried by the New Guinea coastal undercurrent (NGCUC) to Philippine Sea (PS), and is carried by Mindanao Undercurrent (MUC) northward as a salinity minimum of intermediate water. In this study, its spreading and salinity change processes are explored using existing hydrographic data of the World Ocean Database 2013 and Argo floats. Spreading of AAIW is closely associated with the transports of MUC, and is separately carried northward to about 10°N and 15°N by the two branches of MUC. Estimated for subsurface water with salinity is greater than 34.55 psu, the northward geostrophic transport of AAIW by the MUC at 8°N and 12°N is about 9 and 5.5 Sv (1 Sv = 10⁶ m³ s^-1), which is not sensitive to reference level choice. Both diapycnal and isopycnal mixing effects are shown to be elevated in the MUC owing to enhanced salinity gradient near the Halmahera Eddy. We also examined the interannual variations of AAIW spreading, and found which maybe related to ENSO.