Poorly ventilated deep ocean at the Last Glacial Maximum inferred from carbon isotopes: A data-model comparison study

• Published in: Paleoceanography
• Main Authors: Menviel, L, Yu, Jimin, Joos, F., Mouchet, A.T., Meissner, KA, England, Matthew Heathcote
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union
• Subjects: Antarctic; Pacific; Antarc*; North Atlantic Deep Water; North Atlantic
• Online Access: http://hdl.handle.net/1885/247315; https://doi.org/10.1002/2016PA003024; https://openresearch-repository.anu.edu.au/bitstream/1885/247315/4/01_Menviel_Poorly_ventilated_deep_ocean_2017.pdf.jpg

Atmospheric CO2 was ∼90 ppmv lower at the Last Glacial Maximum (LGM) compared to the late Holocene, but the mechanisms responsible for this change remain elusive. Here we employ a carbon isotope-enabled Earth System Model to investigate the role of ocean circulation in setting the LGM oceanic ????13C distribution, thereby improving our understanding of glacial/interglacial atmospheric CO2 variations. We find that the mean ocean ????13C change can be explained by a 378 ± 88 Gt C (2????) smaller LGM terrestrial carbon reservoir compared to the Holocene. Critically, in this model, differences in the oceanic ????13C spatial pattern can only be reconciled with a LGM ocean circulation state characterized by a weak (10–15 Sv) and relatively shallow (2000–2500 m) North Atlantic Deep Water cell, reduced Antarctic Bottom Water transport (≤10 Sv globally integrated), and relatively weak (6–8 Sv) and shallow (1000–1500 m) North Pacific Intermediate Water formation. This oceanic circulation state is corroborated by results from the isotope-enabled Bern3D ocean model and further confirmed by high LGM ventilation ages in the deep ocean, particularly in the deep South Atlantic and South Pacific. This suggests a poorly ventilated glacial deep ocean which would have facilitated the sequestration of carbon lost from the terrestrial biosphere and atmosphere. This project was supported by the Australian Research Council. L. Menviel, and M. England acknowledge funding from the Australian Research Council grants DE150100107 and FL100100214, respectively. J. Yu acknowledges funding from the Australian Research Council grants FT140100993, DP140101393, K. Meissner acknowledges support from a UNSW Faculty of Science Silverstar award. F.J. acknowledges funding by the Swiss National Science Foundation.