Revisiting the Middle Eocene Climatic Optimum ‘Carbon Cycle Conundrum’ with new estimates of atmospheric pCO2 from boron isotopes.

Henehan, Michael, Edgar, Kirsty, Foster, Gavin, Penman, Donald, Hull, Pincelli, Greenop, Rosanna, Anagnostou, Eleni and Pearson, Paul (2020) Revisiting the Middle Eocene Climatic Optimum ‘Carbon Cycle Conundrum’ with new estimates of atmospheric pCO2 from boron isotopes. Open Access Paleoceanography and Paleoclimatology, 35 (6). e2019PA003713. DOI 10.1029/2019PA003713.

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Supplementary data:

Abstract

The Middle Eocene Climatic Optimum (MECO) was a gradual warming event and carbon cycle perturbation that occurred between 40.5 and 40.1 Ma. A number of characteristics, including greater-than-expected deep-sea carbonate dissolution, a lack of globally-coherent negative δ 13 40 C excursion in marine carbonates, a duration longer than the characteristic timescale of carbon-cycle recovery, and the absence of a clear trigger mechanism, challenge our current understanding of the Earth system and its regulatory feedbacks. This makes the MECO one of the most enigmatic events in the Cenozoic, dubbed a middle Eocene ‘carbon cycle conundrum’. Here we use boron isotopes in planktic foraminifera to better constrain pCO2 changes over the event. Over the MECO itself, we find that pCO2 rose by only 0.55-0.75 doublings, thus requiring a much more modest carbon injection than previously indicated by the alkenone δ 13 C-pCO2 proxy. In addition, this rise in pCO2 was focused around the peak of the 400 kyr warming trend. Before this, considerable global carbonate δ 18 O change was asynchronous with any coherent ocean pH (and hence pCO2) excursion. This finding suggests that middle Eocene climate (and perhaps a nascent cryosphere) was highly sensitive to small changes in radiative forcing.

Document Type: Article
Keywords: boron isotopes, pCO2 reconstruction, Middle Eocene Climatic Optimum, carbon cycle, paleoclimate, cryosphere
Research affiliation: NOC
GFZ
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1029/2019PA003713
ISSN: 2572-4517
Projects: IODP
Date Deposited: 04 Mar 2020 10:48
Last Modified: 06 Jul 2020 05:50
URI: http://oceanrep.geomar.de/id/eprint/49104

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