Campbell Plateau: A major control on the SW Pacific sector of the Southern Ocean circulation

Abstract. New Zealand’s subantarctic region is a dynamic oceanographic zone with the Subtropical Front (STF) to the north and the Subantarctic Front (SAF) to the south. Both the fronts and their associated currents are strongly influenced by topography: the South Island of New Zealand and the Chatham Rise for the STF, and Macquarie Ridge and Campbell Plateau for the SAF. Here for the first time we present a consistent picture across the subantarctic region of the relationships between front positions, bathymetry and water mass structure using eight high resolution oceanographic sections that span the region. Our results show that the northwest side of Campbell Plateau is comparatively warm due to a southward extension of the STF over the plateau. The SAF is steered south and east by Macquarie Ridge and Campbell Plateau, with waters originating in the SAF also found north of the plateau in the Bounty Trough. Subantarctic Mode Water (SAMW) formation is confirmed to exist south of the plateau on the northern side of the SAF in winter, while on Campbell Plateau a deep reservoir persists into the following autumn. Antarctic Intermediate Water (AAIW) is observed in the deeper regions around the edges of the plateau, but not on the plateau, confirming that the waters on the plateau are effectively isolated from AAIW and deeper water masses that typify the open Southern Ocean waters.