Disequilibrium and Soft Tissue Pump Contributions to Glacial CO2 Drawdown
Gray, William R. (Université Paris-Saclay)
Trudgill, Molly (Université Paris-Saclay)
Shankle, Madison (University of St. Andrews)
Eggleston, Sarah (Osnabrück University)
de Lavergne, Casimir (Sorbonne University)
Galbraith, Eric (Universitat Autònoma de Barcelona. Institut de Ciència i Tecnologia Ambientals)

Fecha:	2026
Resumen:	A more "efficient" biological pump is thought to have played a key role in glacial CO2 drawdown, with two principal mechanisms invoked to stem the CO2 "leak" from the modern Southern Ocean. The first sees a strengthened soft tissue pump, associated with a reduction in the ocean's "preformed" nutrient inventory. The second sees an increase in air-sea CO2 disequilibrium (termed the disequilibrium pump). We use an Earth system model (CM2Mc) to show the tracers radiocarbon (Δ14C) and oxygen (O2) exhibit distinct sensitivities to these two pumps within the deep ocean: Δ14C is more sensitive to disequilibrium pump changes, whereas O2 is more sensitive to soft tissue pump changes, as expected from the underlying processes. We apply these pump-specific tracer stoichiometries to available deep ocean Δ14C and O2 proxy data from the Last Glacial Maximum (LGM). Despite the sparsity of O2 data, the results show a consistent increase in soft tissue and disequilibrium DIC within the deep ocean of ∼135 μmol/kg, with broadly comparable contributions from the two pumps. Our results imply a reduction in air-sea gas exchange (likely linked to expansion and/or increased isolation of Antarctic Bottom Water), as well as a slowdown of deep ocean overturning and Southern Ocean upwelling at the LGM. Notably, current ocean models struggle to simulate both of these changes simultaneously under glacial forcings. The combined changes in the soft tissue and disequilibrium DIC are of sufficient magnitude to explain the glacial reduction in atmospheric CO2 once a whole ocean alkalinity increase is accounted for.
Nota:	Unidad de excelencia María de Maeztu CEX2019-000940-M
Derechos:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan es reconegui l'autoria de l'obra original.
Lengua:	Anglès
Documento:	Article ; recerca ; Versió publicada
Publicado en:	AGU Advances, Vol. 7, Num. 1 (February 2026) , art. e2025AV002016, ISSN 2576-604X

DOI: 10.1029/2025AV002016

18 p, 666.5 KB

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