Australia: The Land Where Time Began

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Terrestrial Carbon Cycle - Fingerprints of Changes in Response to Large Ocean Circulation Reorganisation

In this paper the authors1 present the results of their investigation into changes in the land, ocean and atmosphere CO2 and carbon by use of the comprehensive carbon cycle-climate model NCAR CSM1.4-carbon. Freshwater perturbations are applied to deep water formation sites in the North Atlantic and Southern Ocean under pre-industrial climate conditions forcing ensemble simulations. This results in the Atlantic Meridional Overturning Circulation (AMOC) being reduced by varying amounts in each experiment. There is a clear distinction between the perturbations in the Northern and Southern Hemispheres, the physical climate fields showing changes that are qualitatively in agreement with results that have been documented in the literature. The biogeochemical cycles, both terrestrial and oceanic, are in in turn affected by the changes in the physical variables, and cause either an increase or decrease in the atmospheric concentration of CO2 of up to 20 ppmv, depending on the location of the perturbation. When the perturbation is in the North Atlantic the land biosphere reacts in some tropical locations and at high northern latitudes with a strong reduction of carbon stocks, though these stocks tend to increase in response to a perturbation in the Southern Hemisphere. The ocean is usually a carbon sink, though throughout various basins large reorganisations occur. The land biosphere responds most strongly in tropical regions, as a result of the Intertropical Convergence Zone being shifted. In South America the carbon fingerprint of this shift can be seen most clearly, whether the shift is to the north or the south, depending on the location where the freshwater is applied. As a result of this a compilation of various proxy records of precipitation changes in the Younger Dryas are compared with the results from the authors1 model. The response to a freshwater perturbation in the North Atlantic shows that the proxy records are generally in good agreement with the response of the model.

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Sources & Further reading

  1. Bozbiyik, A., Steinacher, M., Joos, F., and Stocker, T. F.: Fingerprints of changes in the terrestrial carbon cycle in response to large reorganizations in ocean circulation, Clim. Past Discuss., 6, 1811-1852, doi:10.5194/cpd-6-1811-2010, 2010. 
Author: M. H. Monroe
Last updated: 16/04/2013

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