The atmospheric bridge communicated the δ13C decline during the last deglaciation to the global upper ocean

Shao, Jun; Stott, Lowell D.; Menviel, Laurie; Ridgwell, Andy; Ödalen, Malin; Mohtadi, Mayhar

During the early part of the last glacial termination (17.2–15 ka) and coincident with a inline-formula∼35 ppm rise in atmospheric inline-formulaCO2, a sharp 0.3‰–0.4‰ decline in atmospheric inline-formulaδ13CO2 occurred, potentially constraining the key processes that account for the early deglacial inline-formulaCO2 rise. A comparable inline-formulaδ13C decline has also been documented in numerous marine proxy records from surface and thermocline-dwelling planktic foraminifera. The inline-formulaδ13C decline recorded in planktic foraminifera has previously been attributed to the release of respired carbon from the deep ocean that was subsequently transported within the upper ocean to sites where the signal was recorded (and then ultimately transferred to the atmosphere). Benthic inline-formulaδ13C records from the global upper ocean, including a new record presented here from the tropical Pacific, also document this distinct early deglacial inline-formulaδ13C decline. Here we present modeling evidence to show that rather than respired carbon from the deep ocean propagating directly to the upper ocean prior to reaching the atmosphere, the carbon would have first upwelled to the surface in the Southern Ocean where it would have entered the atmosphere. In this way the transmission of isotopically light carbon to the global upper ocean was analogous to the ongoing ocean invasion of fossil fuel inline-formulaCO2. The model results suggest that thermocline waters throughout the ocean and 500–2000 m water depths were affected by this atmospheric bridge during the early deglaciation.

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Shao, Jun / Stott, Lowell D. / Menviel, Laurie / et al: The atmospheric bridge communicated the δ13C decline during the last deglaciation to the global upper ocean. 2021. Copernicus Publications.

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