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GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L02606, doi:10.1029/2006GL028044, 2007

Observed temperature trends in the Indian Ocean over 1960–1999 and associated mechanisms

Gaël Alory

CSIRO Marine and Atmospheric Research, Hobart, Tasmania, Australia
Wealth from Oceans National Research Flagship, CSIRO, North Ryde, New South Wales, Australia


Susan Wijffels

CSIRO Marine and Atmospheric Research, Hobart, Tasmania, Australia


Gary Meyers

CSIRO Marine and Atmospheric Research, Hobart, Tasmania, Australia
Wealth from Oceans National Research Flagship, CSIRO, North Ryde, New South Wales, Australia


Abstract

The linear trends in oceanic temperature from 1960 to 1999 are estimated using the new Indian Ocean Thermal Archive (IOTA), a compilation of historical temperature profiles. Widespread surface warming is found, as in other data sets, and reproduced in IPCC climate model simulations for the 20th century. This warming is particularly large in the subtropics, and extends down to 800 m around 40–50°S. Models suggest the deep-reaching subtropical warming is related to a 0.5° southward shift of the subtropical gyre driven by a strengthening of the westerly winds, and associated with an upward trend in the Southern Annular Mode index. In the tropics, IOTA shows a subsurface cooling corresponding to a shoaling of the thermocline and increasing vertical stratification. Most models suggest this trend in the tropical Indian thermocline is likely associated with the observed weakening of the Pacific trade winds and transmitted to the Indian Ocean by the Indonesian throughflow.

Received 8 September 2006; accepted 12 December 2006; published 20 January 2007.

Keywords: Indian Ocean; temperature; trend.

Index Terms: 4215 Oceanography: General: Climate and interannual variability (1616, 1635, 3305, 3309, 4513); 4532 Oceanography: Physical: General circulation (1218, 1222); 1620 Global Change: Climate dynamics (0429, 3309); 1635 Global Change: Oceans (1616, 3305, 4215, 4513); 1637 Global Change: Regional climate change.

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Citation: Alory, G., S. Wijffels, and G. Meyers (2007), Observed temperature trends in the Indian Ocean over 1960–1999 and associated mechanisms, Geophys. Res. Lett., 34, L02606, doi:10.1029/2006GL028044.