Warming of the water column in the southwest Pacific Ocean

Abstract

THE response of the deep ocean to long-period temperature variations at the ocean surface is a crucial issue in understanding climate change¹. There are, however, very few observations available for studying changes in the thermal structure of ocean interiors. On the basis of measurements made 22 years apart of full-depth temperature sections in the Pacific Ocean between Australia and New Zealand, we show here that there has been a depth-averaged warming of 0.04 °C and 0.03 °C at 43° S and 28° S, respectively, throughout most of the water column below the mixed layer. The sea-level rise caused by expansion between a depth of 300 m and the ocean floor is 2-3 cm, consistent with the observed rate of global sea-level rise². In the main thermocline there is a coherent cooling and freshening on density surfaces, consistent with surface warming in the Southern Ocean where these waters originate. Similar observations in the North Atlantic³ show comparable changes in the thermal structure and water-mass volumes, but further measurements in other regions are required before firm conclusions can be drawn about the global significance of these changes.