Reversal in Ocean Overturning Circulation During the Eocene Thermal Maximum 2
Abstract
Investigation of Eocene hyperthermals, short-lived periods of extreme warming, is crucial to understanding the sensitivity of ocean/atmosphere dynamics to warming, in particular the ocean's overturning circulation. The most extreme hyperthermal on record is the Paleocene-Eocene Thermal Maximum (PETM), which resulted in an abrupt reorganization of deep ocean circulation (i.e., deep-water formation) as recorded by the C isotopic composition of benthic foraminifera and seafloor carbonate dissolution patterns. Deep water formation and thermohaline circulation maintain basin-to-basin C isotope gradients as deep water masses age, progressively accumulating low-13C/12C respired C. This is recorded as a reversal in the Atlantic-to-Pacific gradient during the PETM. Eocene Thermal Maximum 2 (ETM2) is also a period of interest in which global temperatures increased rapidly due to injection of carbon and for which circulation may have changed akin to the PETM. Initial investigation of ETM2 benthic C isotope records from the Atlantic and Pacific indeed support a reversal in deep circulation. Interpretation of these records requires verification by independent proxies of water mass "age." For this study, we utilize one such proxy, the ratio of B/Ca of benthic forams, which can co-vary with the carbonate content [CO32-] of ambient water. To assess changes in basin-to-basin bottom water [CO32-] gradients, we sampled sediments spanning ETM2 at Ocean Drilling Program sites 1210 located on Shatsky Rise in the Pacific and 1267 at Walvis Ridge in the Atlantic. The unique combination of basin-to-basin C isotope and B/Ca records provides strong constraints on models of ocean carbon cycling and circulation during ETM2. Sensitivity experiments using the CYCLOPS box model can reproduce our preliminary C isotope data when forced with a range of thermohaline circulation "reversal" scenarios via a switch from North Atlantic to North Pacific deep-water formation. However, the magnitudes of both the CIE and carbonate dissolution response exceed observational constraints indicating a more complex response in ocean circulation and other processes that influence bottom water carbonate chemistry.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP31E1682H
- Keywords:
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- 9604 Cenozoic;
- INFORMATION RELATED TO GEOLOGIC TIME;
- 4914 Continental climate records;
- PALEOCEANOGRAPHY;
- 4928 Global climate models;
- PALEOCEANOGRAPHY;
- 4954 Sea surface temperature;
- PALEOCEANOGRAPHY