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Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years

Thornalley, David J.R.; Oppo, Delia W.; Ortega, Pablo; Robson, Jon I.; Brierley, Chris M.; Davis, Renee; Hall, Ian R.; Moffa-Sanchez, Paola; Rose, Neil L.; Spooner, Peter T.; Yashayaev, Igor; Keigwin, Lloyd D.

Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years Thumbnail


Authors

David J.R. Thornalley

Delia W. Oppo

Pablo Ortega

Jon I. Robson

Chris M. Brierley

Renee Davis

Ian R. Hall

Neil L. Rose

Peter T. Spooner

Igor Yashayaev

Lloyd D. Keigwin



Abstract

The Atlantic meridional overturning circulation (AMOC) is a system of ocean currents that has an essential role in Earth’s climate, redistributing heat and influencing the carbon cycle1, 2. The AMOC has been shown to be weakening in recent years1; this decline may reflect decadal-scale variability in convection in the Labrador Sea, but short observational datasets preclude a longer-term perspective on the modern state and variability of Labrador Sea convection and the AMOC1, 3,4,5. Here we provide several lines of palaeo-oceanographic evidence that Labrador Sea deep convection and the AMOC have been anomalously weak over the past 150 years or so (since the end of the Little Ice Age, LIA, approximately ad 1850) compared with the preceding 1,500 years. Our palaeoclimate reconstructions indicate that the transition occurred either as a predominantly abrupt shift towards the end of the LIA, or as a more gradual, continued decline over the past 150 years; this ambiguity probably arises from non-AMOC influences on the various proxies or from the different sensitivities of these proxies to individual components of the AMOC. We suggest that enhanced freshwater fluxes from the Arctic and Nordic seas towards the end of the LIA—sourced from melting glaciers and thickened sea ice that developed earlier in the LIA—weakened Labrador Sea convection and the AMOC. The lack of a subsequent recovery may have resulted from hysteresis or from twentieth-century melting of the Greenland Ice Sheet6. Our results suggest that recent decadal variability in Labrador Sea convection and the AMOC has occurred during an atypical, weak background state. Future work should aim to constrain the roles of internal climate variability and early anthropogenic forcing in the AMOC weakening described here.

Citation

Thornalley, D. J., Oppo, D. W., Ortega, P., Robson, J. I., Brierley, C. M., Davis, R., …Keigwin, L. D. (2018). Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years. Nature, 556(7700), 227-230. https://doi.org/10.1038/s41586-018-0007-4

Journal Article Type Article
Acceptance Date Feb 13, 2018
Online Publication Date Apr 11, 2018
Publication Date Apr 11, 2018
Deposit Date Feb 28, 2019
Publicly Available Date Mar 28, 2024
Journal Nature
Print ISSN 0028-0836
Electronic ISSN 1476-4687
Publisher Nature Research
Peer Reviewed Peer Reviewed
Volume 556
Issue 7700
Pages 227-230
DOI https://doi.org/10.1038/s41586-018-0007-4
Related Public URLs http://orca.cf.ac.uk/110650/

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