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Abrupt North Atlantic circulation changes in response to gradual CO2 forcing in a glacial climate state

Zhang, Xu, Knorr, Gregor, Lohmann, Gerrit and Barker, Stephen 2017. Abrupt North Atlantic circulation changes in response to gradual CO2 forcing in a glacial climate state. Nature Geoscience 10 , pp. 518-523. 10.1038/ngeo2974

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Abstract

Glacial climate is marked by abrupt, millennial-scale climate changes known as Dansgaard–Oeschger cycles. The most pronounced stadial coolings, Heinrich events, are associated with massive iceberg discharges to the North Atlantic. These events have been linked to variations in the strength of the Atlantic meridional overturning circulation. However, the factors that lead to abrupt transitions between strong and weak circulation regimes remain unclear. Here we show that, in a fully coupled atmosphere–ocean model, gradual changes in atmospheric CO2 concentrations can trigger abrupt climate changes, associated with a regime of bi-stability of the Atlantic meridional overturning circulation under intermediate glacial conditions. We find that changes in atmospheric CO2 concentrations alter the transport of atmospheric moisture across Central America, which modulates the freshwater budget of the North Atlantic and hence deep-water formation. In our simulations, a change in atmospheric CO2 levels of about 15 ppmv—comparable to variations during Dansgaard–Oeschger cycles containing Heinrich events—is sufficient to cause transitions between a weak stadial and a strong interstadial circulation mode. Because changes in the Atlantic meridional overturning circulation are thought to alter atmospheric CO2 levels, we infer that atmospheric CO2 may serve as a negative feedback to transitions between strong and weak circulation modes.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Uncontrolled Keywords: Atmospheric dynamics Climate and Earth system modelling Palaeoclimate
Publisher: Nature Publishing Group
ISSN: 1752-0894
Funders: NERC
Date of First Compliant Deposit: 22 June 2017
Date of Acceptance: 23 May 2017
Last Modified: 27 Feb 2018 20:17
URI: http://orca.cf.ac.uk/id/eprint/101675

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