Current Measurements in the Halmahera Sea

A mooring with current meters at 400, 700, and 900 m at the 950-m isobath south of the 700-m-deep sill across the Halmahera Sea revealed many signals between June 1993 and July 1994. Strong tidal currents of 50 cm/s dragged the mooring down by as much as 80 m on occasions when the lunar perigees corresponded with new or full moons. At 400 m the nontidal currents were southward at up to 25 cm/s from October to April and northwestward at up to 20 cm/s at other times. At 700-m depth there was a near-continuous nontidal southward flow of 9 cm/s across the sill into the Halmahera Basin, which accords with findings by earlier Dutch and Indonesian workers. The current meter at 900-m depth showed the nontidal flow to be weak (∼1 cm/s) to the west. The southward transport between 350 and 700 m was inferred to reach a maximum of 5 Sv during the NW monsoon, with the annual mean being 1.5 Sv. There was a spring-neap effect on the nontidal currents at 400 m that was most pronounced in the last few months of the mooring's life: these currents changed from ∼10 cm/s to the east during neap tides to ∼20 cm/s to the NNW during spring tides. Temperature and salinity profiles suggest that the waters of the Halmahera Sea are derived in part from the New Guinea Coastal Undercurrent.