Meridional volume transport in the South Pacific: Mean and SAMrelated variability

Abstract The large increase in upper-ocean sampling during the past decade enables improved estimation of the mean meridional volume transport in the midlatitude South Pacific, and hence of the climatically important Meridional Overturning Circulation. Transport is computed using Argo float profile data for geostrophic shear and trajectory data for reference velocities at 1000 m. For the period 2004–2012, the mean geostrophic transport across 32 S is 20.66 6.0 Sv in the top 2000 m of the ocean. From west to east, this includes the southward East Australian Current (23.36 2.9 Sv), its northward recirculation (16.36 3.6 Sv), the broad interior northward flow (18.46 4.1 Sv), and the net northward flow (9.26 2.2 Sv) in opposing currents in the eastern Pacific. The basin-integrated geostrophic transport includes 7.36 0.9 Sv of surface and thermocline waters, 4.96 1.0 Sv of Subantarctic Mode Water, and 4.96 1.4 Sv of Antarctic Intermediate Water. Interannual variability in volume transport across 32 S in the South Pacific shows a Southern Annual Mode signature characterized by an increase during the positive phase of the Southern Annular Mode and a decrease during the negative phase. Maximum amplitudes in geostrophic transport anomalies, seen in the East Australian Current and East Australian Current recirculation, are consistent with wind stress curl anomalies near the western boundary.