Absolute geostrophic velocity within the Subantarctic front in the PacificOcean

Velocity measurements from a shipboard acoustic Doppler current profiler (A DCP) are used as a reference for geostrophic current calculations on six se ctions across the Subantarctic Front (SAF) in the Pacific Ocean. The result ing cross-track velocity estimates near the bottom range from 4 to 10 cm s( -1) to the east in the eastward jet at the SAF: in adjacent regions of west ward surface flow, the near-bottom velocity is usually to the west. On one section where simultaneous lowered ADCP velocity profiles are available, th ey confirm the results from the shipboard ADCP. Annual mean velocity sectio ns from the Parallel Ocean Program I numerical model also show near-bottom velocities exceeding 5 cm s(-1), with the same tendency for the zonal veloc ity component near the bottom to match the direction of the surface jets. T ransport across the entire Antarctic Circumpolar Current (ACC) cannot be es timated accurately from ADCP-referenced geostrophic sections because even a very small cross-track bias integrates to a large error. A preliminary loo k at the 1992 model transport stream function shows that the effect of bott om-referencing varies from section to section; it can cause 40-Sv recircula tions to be missed, and can cause net transport to be underestimated or ove restimated by O (30 Sv).