A climatology of the circulation and water mass distribution near the Philippine coast

This study provides a climatology of the circulation and water mass distrib ution by using historical data combined with observations from dozens of re cent cruises near the Philippine coast. The most striking results are relat ed to the poleward contraction of the subtropical gyre on denser surfaces, with the bifurcation of the North Equatorial Current moving from about 15 d egrees N in the upper thermocline to about 20 degrees N at intermediate dep ths. Though time variability and the possible errors in the data are rather large, the Halmahera eddy (IIE) is clearly seen in the climatic mean field s, lying at about 3 degrees N, 130 degrees E near the surface and reaching the Mindanao coast on density surfaces around 27.2 sigma(theta). It seems t hat the previously observed Mindanno Undercurrent is merely a component of the recirculation associated with the HE, North Pacific Tropical Water (NPT W) and Intermediate Water (NPIW) enter the western ocean with their extreme properties centered at 15 degrees and 20 degrees N, respectively, and cont inue southward as far as the southern tip of Mindanao along the western bou ndary. The influence of South Pacific sources becomes increasingly importan t with depth, antarctic Intermediate Water (AAIW) is traced to about 12 deg rees N off Mindanao: but, there is little indication of a northward Row of AAIW farther north. Salinity extremes are also used as an indicator of NPTW and NPIW and the primary result is that mixing of potential temperature an d salinity are not jointly compensated, thus leading to an increase of dens ity in NPTW and a decrease of density in NPIW in the flowpath from the Nort h Pacific subtropical gpre to the Tropics along the Philippine coast.