The Atmospheric Bridge Communicated the δ13C Decline during the Last Deglaciation to the Global Upper Ocean

• Main Authors: Shao, Jun, Stott, Lowell D, Menviel, Laurie, Ridgwell, Andy, Ödalen, Malin, Mohtadi, Mayhar
• Format: Text
• Language: English
• Published: 2020
• Subjects: Southern Ocean; Pacific
• Online Access: https://doi.org/10.5194/cp-2020-95; https://cp.copernicus.org/preprints/cp-2020-95/

During the early last glacial termination (17.2–15 ka) atmospheric δ 13 C declined sharply by 0.3–0.4 ‰ as atmospheric pCO 2 rose. This was the initial part of the atmospheric δ 13 C excursion that lasted for multiple thousand years. A similar δ 13 C decline has been documented in marine proxy records from both surface and thermocline-dwelling planktic foraminifera. The foraminiferal δ 13 C decline has previously been attributed to a flux of respired carbon from the deep ocean that was subsequently transported within the upper ocean (i.e. <q>bottom up</q> transport) to sites where the signal is recorded. Here, we provide modeling evidence that when respired carbon upwells in the Southern Ocean, negative δ 13 C anomalies in the global upper ocean were instead transferred from the atmosphere (i.e. top down transport). Due to this efficient <q>atmospheric bridge</q>, the pathway of δ 13 C transport was likely to be different from nutrient transport during the early deglaciation. This implies that the usage of planktic δ 13 C records for identifying the carbon source(s) responsible for the atmospheric pCO 2 rise during the early deglaciation is limited. The model results also suggest that thermocline waters in upwelling systems like the eastern equatorial Pacific, and even upper deep waters above 2000 m, can be affected by this atmospheric bridge during the early deglaciation. Our results imply that caution must be applied when interpreting early deglacial marine δ 13 C records from depths that are potentially affected by the atmosphere.