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, J., Joos, Fortunat, Mouchet, A., Meissner, K. J., England, M. H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2017
• Subjects: 530 Physics; 550 Earth sciences & geology; Antarctic; Pacific; Antarc*; North Atlantic Deep Water; North Atlantic
• Online Access: https://boris.unibe.ch/100806/1/Menviel_et_al-2017-Paleoceanography.pdf; https://boris.unibe.ch/100806/; http://onlinelibrary.wiley.com/doi/10.1002/2016PA003024/abstract

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 δ¹³C distribution, thereby improving our understanding of glacial/interglacial atmospheric CO₂ variations. We find that the mean ocean δ¹³C change can be explained by a 378 ± 88 Gt C(2σ) smaller LGM terrestrial carbon reservoir compared to the Holocene. Critically, in this model, differences in the oceanic δ¹³C 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.