Energetic subthermocline currents observed east of Mindanao

Two cruises of the JAMSTEC ship Kaiyo, during October 1999 and September 2000, included lowered acoustic Doppler current profiler (ADCP) measurements to 2000 m depth on zonal sections extending east from the Mindanao coast. On the second cruise, the lowered ADCP profiles were augmented by profiles to 1000 m from a 38-kHz shipboard ADCP. All zonal LADCP sections (7°N, 8°, 10°) showed southward flow along the coast extending to at least 2000 m depth. Although the Mindanao current in the upper 500 m forms a continuous narrow stream along the coast, the deeper southward flow appears to be part of a set of subthermocline eddies within 300 km of the coast; northward flow was found 100-200 km offshore during both cruises. Currents mapped by the shipboard ADCP on the second cruise indicate that cyclonic eddies were centered near 7.5°N, 128°E and 10.2°N, 127°E. Maximum speeds of 0.6 m s−1 were observed at 800 m depth on the 10°N section, and speeds of 0.2-0.3 m s−1 were found below 1500 m on all sections.