Circulation and hydrology off the west coast of the South Island, New Zealand

In April 1974, the formation of the Southland Current was evident in the geostrophic circulation off the west coast of the South Island. A broad inflow of subtropical water towards the coast near 42° S was turned to the south by the topographic constraints of the Challenger Plateau and the continental slope. Near Jackson Head at 44° S, where the continental slope steepens, the current strengthens to form the well‐defined Southland Current. Volume transports indicate that this current is almost fully developed off the Piordland coast. The Westland Current was not evident in the geostrophic circulation and this, taken with previous work, suggests this current is locally wind driven. Hydrologically, the area could be divided into a coastal zone, extending between 35 km and 100 km offshore, and an oceanic zone. An estimate of the effect of freshwater runoff using a simple mixing model showed that 1% of the water over the shelf was runoff, and that this affected the salinity of 37% of the water over the shelf.