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


Contact
Xu.Zhang [ at ] awi.de

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
Authors
Divisions
Primary Division
Programs
Primary Topic
Publication Status
Published
Eprint ID
45463
DOI 10.1038/ngeo2974

Cite as
Zhang, X. , Knorr, G. , Lohmann, G. and Barker, S. (2017): Abrupt North Atlantic circulation changes in response to gradual CO2 forcing in a glacial climate state , Nature Geoscience, 10 (7), pp. 518-523 . doi: 10.1038/ngeo2974


Download
[thumbnail of ZhangNGS.pdf]
Preview
PDF
ZhangNGS.pdf

Download (3MB) | Preview
Cite this document as:
[thumbnail of ZhangNGSSI.pdf]
Preview
PDF
ZhangNGSSI.pdf

Download (13MB) | Preview
Cite this document as:

Share
Add to AnyAdd to TwitterAdd to FacebookAdd to LinkedinAdd to PinterestAdd to Email


Citation

Geographical region

Research Platforms
N/A

Campaigns
N/A


Actions
Edit Item Edit Item