Increased nutrient supply to the Southern Ocean during the Holocene and its implications for the pre-industrial atmospheric CO 2 rise

A rise in the atmospheric CO 2 concentration of ~20 parts per million over the course of the Holocene has long been recognized as exceptional among interglacials and is in need of explanation. Previous hypotheses involved natural or anthropogenic changes in terrestrial biomass, carbonate compensatio...

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Bibliographic Details
Published in:Nature Geoscience
Main Authors: Studer, Anja S., Sigman, Daniel M., Martínez-García, Alfredo, Thöle, Lena M., Michel, Elisabeth, Jaccard, Samuel L., Lippold, Jörg A., Mazaud, Alain, Wang, Xingchen T., Robinson, Laura F., Adkins, Jess F., Haug, Gerald H.
Format: Article in Journal/Newspaper
Language:English
Published: 2018
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Online Access:https://hdl.handle.net/1983/59f1368d-42cb-4ae9-a700-45e6b18dfd7c
https://research-information.bris.ac.uk/en/publications/59f1368d-42cb-4ae9-a700-45e6b18dfd7c
https://doi.org/10.1038/s41561-018-0191-8
https://research-information.bris.ac.uk/ws/files/161197436/Studer_2018_NatGeo.pdf
http://www.scopus.com/inward/record.url?scp=85051119653&partnerID=8YFLogxK
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Summary:A rise in the atmospheric CO 2 concentration of ~20 parts per million over the course of the Holocene has long been recognized as exceptional among interglacials and is in need of explanation. Previous hypotheses involved natural or anthropogenic changes in terrestrial biomass, carbonate compensation in response to deglacial outgassing of oceanic CO 2 , and enhanced shallow water carbonate deposition. Here, we compile new and previously published fossil-bound nitrogen isotope records from the Southern Ocean that indicate a rise in surface nitrate concentration through the Holocene. When coupled with increasing or constant export production, these data suggest an acceleration of nitrate supply to the Southern Ocean surface from underlying deep water. This change would have weakened the ocean’s biological pump that stores CO 2 in the ocean interior, possibly explaining the Holocene atmospheric CO 2 rise. Over the Holocene, the circum-North Atlantic region cooled, and the formation of North Atlantic Deep Water appears to have slowed. Thus, the ‘seesaw’ in deep ocean ventilation between the North Atlantic and the Southern Ocean that has been invoked for millennial-scale events, deglaciations and the last interglacial period may have also operated, albeit in a more gradual form, over the Holocene.