Aspects of the structure and variability of the low‐salinity‐layer in Doubtful Sound, a New Zealand fiord

Abstract

The concurrent actions of fresh water input from the Manapouri power station and the extreme precipitation in the catchment of Doubtful Sound, south‐western New Zealand, results in the maintenance of a surface low‐salinity‐layer (LSL). Although the role of the LSL in controlling subtidal and inter‐tidal assemblages in Doubtful Sound has been documented, little is presently known about the characteristics of the LSL itself. The work presented here aims to elucidate particular aspects of the structure and variability of this ecologically important feature. Synoptic hydrographic data collected during the Doubtful Sound Monitoring Program (DSMP) shows that the LSL is robust and maintained throughout all seasons. Furthermore, hourly salinity and temperature data acquired from four sites within Doubtful Sound show that the major source of variability in the LSL lies in the weather bands although the surface temperatures also exhibited a seasonal component. Time‐series analyses of these data revealed that large perturbations in the LSL were associated with the combined actions of the local wind stress and precipitation. In addition, analysis of data from moored quantum PAR (photosynthetically active radiation) sensors revealed the important influence of the LSL on the subsurface light field.