WARMING OF THE WATER COLUMN IN THE SOUTHWEST PACIFIC-OCEAN

THE response of the deep ocean to long-period temperature variations at the ocean surface is a crucial issue in understanding climate change 1. 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-degrees-C and 0.03-degrees-C at 43-degrees-S and 28-degrees-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 rise 2. 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 Atlantic 3 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.