Enhanced Mid-depth Southward Transport in the Northeast Atlantic at the Last Glacial Maximum Despite a Weaker AMOC

While previous studies consistently suggest that North Atlantic Deep Water (NADW) was shallower at the Last Glacial Maximum (LGM) than at pre-industrial, its strength is still controversial. Here, using a series of LGM experiments, we show that proxy records are consistent with a shallower and ∼50%...

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Bibliographic Details
Published in:Paleoceanography and Paleoclimatology
Main Authors: Menviel, L, Spence, P., Skinner, L. C., Tachikawa, K, Friedrich, Tobias, Missiaen, L., Yu, Jimin
Format: Article in Journal/Newspaper
Language:English
Published: Wiley
Subjects:
Antarctic
Norwegian Sea
Mid-Atlantic Ridge
Antarc*
NADW
North Atlantic Deep Water
North Atlantic
Northeast Atlantic
Northwest Atlantic
Sea ice
Online Access:http://hdl.handle.net/1885/217351
https://doi.org/10.1029/2019PA003793
https://openresearch-repository.anu.edu.au/bitstream/1885/217351/3/01_Menviel_Enhanced_Mid-depth_Southward_2020.pdf.jpg
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Summary:While previous studies consistently suggest that North Atlantic Deep Water (NADW) was shallower at the Last Glacial Maximum (LGM) than at pre-industrial, its strength is still controversial. Here, using a series of LGM experiments, we show that proxy records are consistent with a shallower and ∼50% weaker NADW, associated with a ∼3◦ equatorward shift of the sea ice edge and convection sites in the Norwegian Sea. A shoaling and weakening of NADW further allow penetration of Antarctic Bottom Water in the North Atlantic, despite Antarctic Bottom Water transport being reduced by ∼40%. While the Deep Western Boundary Current in the northwest Atlantic weakens with NADW, the mid-depth southward flow on the east side of the north Mid-Atlantic Ridge strengthens, consistent with paleorecords. This northeast Atlantic intensification is due to a change in density gradients: a weaker AMOC reduces the transport of equatorial waters to the northeast Atlantic, thus weakening the North Atlantic zonal density gradient. The resultant globally weaker oceanic circulation at the LGM would have contributed to an increase in oceanic carbon content and thus a decrease in atmospheric CO2 concentration. This project was supported by the Australian Research Council. L. C. M., L. M., P. S., and J. Y. acknowledge funding from the Australian Research Council Grants DE150100107, DP180100048, DE150100223, FT140100993, FT180100606, and DP140101393. L. C. S. acknowledges support from NERC Grant NE/L006421/1.

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