Circulation and Heat Flux along the Western Boundary of the North Pacific

On the basis of the conductivity temperature depth (CTD) observation data off the coast of the Philippines (7.5˚–18˚N, 130˚E–the east coast of the Philippines) in the fall of 2005, the water mass distribution, geostrophic flow field, and heat budget are examined. Four water masses are present: the North Pacific Tropical Surface Water, the North Pacific Sub-surface Water, the North Pacific Intermediate Water, and the Antarctic Intermediate Water (AAIW). The previous three corresponded with the North Equatorial Current (NEC), the Kuroshio Current (KC), and the Mindanao Current (MC), respectively. AAIW is the source of the Mindanao Undercurrent. The mass transport of NEC, KC, and MC is 58.7, 15, and 27.95 Sv, respectively (relative to 1500 db). NEC can be balanced by the transport across the whole transect 18˚N (31.81 Sv) and 7.5˚N (26.11 Sv) but not simply by KC and MC. Direct calculation is used to study the heat flux. In sum, 1.45 PW heat is transported outwards the observed region, which is much more than that released from the ocean to the air at the surface (0.05 PW). The net heat lost decreased the water temperature by 0.75℃ each month on average, and the trend agreed well with the SST change. Vertically, the heat transported by the currents is mainly completed in the upper 500 m.