Response of the North Atlantic thermohaline circulation and ventilation to increasing carbon dioxide in CCSM3


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dc.contributor.author Bryan, Frank O.
dc.contributor.author Danabasoglu, Gokhan
dc.contributor.author Nakashiki, Norikazu
dc.contributor.author Yoshida, Yoshikatsu
dc.contributor.author Kim, Dong-Hoon
dc.contributor.author Tsutsui, Junichi
dc.contributor.author Doney, Scott C.
dc.date.accessioned 2010-12-07T14:46:43Z
dc.date.available 2010-12-07T14:46:43Z
dc.date.issued 2006-06-01
dc.identifier.citation Journal of Climate 19 (2006): 2382–2397 en_US
dc.identifier.uri http://hdl.handle.net/1912/4174
dc.description Author Posting. © American Meteorological Society 2006. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 19 (2006): 2382–2397, doi:10.1175/JCLI3757.1. en_US
dc.description.abstract The response of the North Atlantic thermohaline circulation to idealized climate forcing of 1% per year compound increase in CO2 is examined in three configurations of the Community Climate System Model version 3 that differ in their component model resolutions. The strength of the Atlantic overturning circulation declines at a rate of 22%–26% of the corresponding control experiment maximum overturning per century in response to the increase in CO2. The mean meridional overturning and its variability on decadal time scales in the control experiments, the rate of decrease in the transient forcing experiments, and the rate of recovery in periods of CO2 stabilization all increase with increasing component model resolution. By examining the changes in ocean surface forcing with increasing CO2 in the framework of the water-mass transformation function, we show that the decline in the overturning is driven by decreasing density of the subpolar North Atlantic due to increasing surface heat fluxes. While there is an intensification of the hydrologic cycle in response to increasing CO2, the net effect of changes in surface freshwater fluxes on those density classes that are involved in deep-water formation is to increase their density; that is, changes in surface freshwater fluxes act to maintain a stronger overturning circulation. The differences in the control experiment overturning strength and the response to increasing CO2 are well predicted by the corresponding differences in the water-mass transformation rate. Reduction of meridional heat transport and enhancement of meridional salt transport from mid- to high latitudes with increasing CO2 also act to strengthen the overturning circulation. Analysis of the trends in an ideal age tracer provides a direct measure of changes in ocean ventilation time scale in response to increasing CO2. In the subpolar North Atlantic south of the Greenland–Scotland ridge system, there is a significant increase in subsurface ages as open-ocean deep convection is diminished and ventilation switches to a predominance of overflow waters. In middle and low latitudes there is a decrease in age within and just below the thermocline in response to a decrease in the upwelling of old deep waters. However, when considering ventilation within isopycnal layers, age increases for layers in and below the thermocline due to the deepening of isopycnals in response to global warming. en_US
dc.format.mimetype application/pdf
dc.language.iso en_US en_US
dc.publisher American Meteorological Society en_US
dc.relation.uri http://dx.doi.org/10.1175/JCLI3757.1
dc.title Response of the North Atlantic thermohaline circulation and ventilation to increasing carbon dioxide in CCSM3 en_US
dc.type Article en_US
dc.identifier.doi 10.1175/JCLI3757.1

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