Hydrology and near‐surface nutrient distribution along the South Otago continental shelf, New Zealand, in summer and winter 1986

Abstract

The 3 Otago coastal water masses (Neritic water, subtropical Southland Current water, and Subantarctic Surface Water) defined in the literature were identified on 1 cruise in early summer and 1 in mid winter. Winter results showed that Neritic water is derived from the Clutha River. During winter the Southland Current was characterised by temperatures between 9.0 and 10.6°C and a salinity range of 34.4 to 34.9 × 10 ‐3 . During summer a thermocline and pycnocline were observed at 30–50 m depth sloping down toward the coast. Low‐salinity Neritic water was less apparent than in winter. Summer nutrient levels were depleted over all of the continental shelf, relative to winter. This is probably caused by the enclosure of coastal surface waters inshore of the pycnocline. Reactive Si was conservative in winter regardless of water mass. Reactive P was approximately constant in Neritic water and Southland Current water. In summer, neither nutrient was conservative.