Detecting thermohaline circulation changes from ocean properties in a coupled model

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GEOPHYSICAL RESEARCH LETTERS, VOL. 31, L13204, doi:10.1029/2004GL020218, 2004 Detecting thermohaline circulation changes from ocean properties in a coupled model Aixue Hu Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, Colorado, USA Gerald A. Meehl Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, Colorado, USA Weiqing Han Program in Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado, USA Abstract Significant changes of the thermohaline circulation (THC) are likely to cause abrupt climate change. Here we intend to find a simple measure to detect changes in THC through examining several factors proposed to control the THC variations using a coupled climate model. These factors are equatorial-South Atlantic upper ocean temperature, Southern Ocean freshening, inter-basin sea surface salinity contrast, and meridional steric height gradient. Three experiments are analyzed – a present-day control run, a freshwater hosing run and a 1% CO2 run. Results show that if freshwater flux is the primary cause, all examined factors can predict the THC changes. If both thermal and haline forcings are involved, only the Atlantic meridional steric height gradient gives a consistent measure of the THC variations. A new result presented here is that the inter-basin sea surface temperature contrast between North Atlantic and North Pacific is found to be an indicator of THC changes. Received 9 April 2004; accepted 9 June 2004; published 3 July 2004.