Carbon Fluxes during Dansgaard-Oeschger Events as Simulated by an Earth System Model

Publikation: Bidrag til tidsskriftTidsskriftartikelForskningfagfællebedømt

The Community Earth System Model with marine and terrestrial biogeochemistry is configured to simulate glacial climate. The integration shows transitions from warm to cold states}interstadials to stadials}and back. The amplitude of the associated Greenland and Antarctica temperature changes and the atmospheric CO2 signal are consistent with ice-core reconstructions, and so are the time lags between termination of a stadial, Antarctic temperature reversal, and the decline of the atmospheric CO2 concentration (for brevity's sake simply referred to as CO2 from here on). The present model results stand out because the transitions occur spontaneously (without forcing changes like hosing) and because they reproduce the observed features above in a configuration that uses the same parameterizations as climate simulations for the present day (i.e., no retuning has been done). During stadials, precipitation shifts lead to reduced growth on land, which dominates the CO2 increase; the ocean acts as a minor carbon sink during the stadials. After the end of the stadials, however, the sudden reversal of the stadial anomalies in temperature, wind, and precipitation turns the ocean into a carbon source, which accounts for the continued rise of CO2 for several hundred years into the interstadial. The simulations also provide a novel possible interpretation for the observed correlation between CO2 and Antarctic temperature: rather than both being controlled by Southern Ocean processes, they are both controlled by the North Atlantic Ocean, and most of the extra CO2 may not be of Southern Hemisphere origin. If the stadials are prolonged through North Atlantic hosing, the upper ocean comes to an equilibrium, and the CO2 response is dominated by a single process: reduced export production in the North Atlantic as result of the collapsed overturning circulation. This is in contrast to the unforced simulation where the net ocean carbon flux anomaly is the sum of several regional responses of both signs and similar magnitudes. Reducing the aeolian iron deposition by half, to account for the observed reduction of Southern Hemisphere dust fluxes during stadials, reduces biological productivity and export production so that the Southern Ocean emerges as an important carbon source, at least for the three centuries up until a new equilibrium for the upper ocean is reached.

TidsskriftJournal of Climate
Udgave nummer17
Sider (fra-til)5745-5758
Antal sider14
StatusUdgivet - 1 sep. 2022

Bibliografisk note

Funding Information:
Acknowledgments. We are grateful to Matthew Long and David Lawrence for their patience in explaining the details of the CESM biogeochemistry. The manuscript was improved greatly by the suggestions of one anonymous referee, Julia Gottschalk, Thomas Bauska, and the editor Shawn Marshall. The computations were done at the Danish Center of Climate Computing at the Niels Bohr Institute, Copenhagen. MJ and RN were supported by Copenhagen University, SOR by the VILLUM Foundation through IceFlow, JP received support from the Australian Government Department of Industry, Science, Energy and Resources (Grant ASCI000002). GV by the Carlsberg Foundation through ChronoClimate, and ZC was partially supported by the Australian Government through the Australian Research Council’s Discovery Projects funding scheme (project DP180102357).

Publisher Copyright:
© 2022 American Meteorological Society.

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