Variability in the Southland Current, New Zealand

Abstract

Current meter moorings were deployed in six locations around the South Island, New Zealand, in 1993 to monitor the Southland Current. Off the eastern shelf of the South Island, the Southland Current is unidirectional, but variable in speed. Mean flows during 6 months at the 100 m isobath off Oamaru and Nugget Pt were 14.4 and 23.8 cm s⁻¹, respectively, with standard deviations of 9 and 14.8 cm s⁻¹. Flows south of Stewart Island, over the Snares Plateau, are more isotropic and considerably weaker, with mean flows typically 3–5 cm s⁻¹. Currents off Oamaru are correlated with those off Nugget Pt, and the dispersion relationship calculated between them indicates phase and group propagation to the north‐east along the coast comparable to that expected for coastally‐trapped waves (CTW). Currents in Foveaux St are strongly wind‐driven, but currents over the Snares Plateau show almost no coherence with the Invercargill wind. An empirical model, using the currents over the Snares Plateau and the Invercargill wind as inputs, can explain up to 0.76 of the variance of the Southland Current.