Near-surface water temperatures in Doubtful Sound and response to natural and anthropogenic drivers

Abstract New Zealand fiords frequently feature a buoyant low-salinity layer (LSL) leading to unique biological communities on their rock walls. The LSL has previously been distinguished by its temperature, but we show this is not always reliable. We describe temporal and spatial patterns in water temperature in Doubtful Sound, and the influences of rainfall, wind, air temperature and the discharge from the Manapōuri hydroelectric power scheme. Surface (0.5 to 19 m depth) temperatures in the fiords varied considerably at frequencies corresponding with season and weather. Distinct weather events coincided with fluctuations in surface temperatures of 5 °C to 10 °C, a magnitude of temperature change comparable to seasonal variability. Variability of surface water temperatures declined with proximity to the hydroelectric discharge. Statistical analyses indicated that changes in climate and weather are likely to have a larger effect on temperatures than changes in the rate of freshwater discharge.