Miocene North Atlantic Sea Surface and Thermocline Temperature Variations (20-8 Ma)
Abstract
The Miocene Climatic Optimum (MCO) was a period of global warming spanning roughly 17 to 14.7 million years ago followed by a period of global cooling, during which a permanent Antarctic ice sheet formed. The North Atlantic plays a key role in regulating ocean water circulation and global climates; however, only sparse data from this interval exists regarding sea surface temperatures. We reconstructed the thermal water column structure of the central subtropical North Atlantic gyre during the MCO and the subsequent period of cooling and ice sheet expansion (14.7-10 Ma) by analyzing four species of foraminifera from subtropical North Atlantic Site 558 (37.8°N latitude) for stable isotopes of carbon and oxygen: surface dwellers D. altispira and Gs. quadrilobatus, thermocline dweller Gq. venezuelana, and benthic P. wuellerstorfi. Following the MCO (14.7-13 Ma), the d18O of the thermocline and surface dwelling species increased by >1‰. Continental ice growth increased global d18Osw by 0.5‰ at this time (Cramer et al., 2011), suggesting at least 2°C cooling in the mixed layer and thermocline. The difference in δ18O values between thermocline and surface dwelling species (i.e. stronger thermocline) increased between 14.8-13.8 Ma, coinciding with the development of a largely permanent East Antarctic Ice Sheet (EAIS). This is similar to previous reports of Middle to Late Miocene surface temperatures from North Atlantic Site 608 (43°N), linking the development of a strong thermocline with high latitude cooling.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP13E1371G
- Keywords:
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- 9325 Atlantic Ocean;
- GEOGRAPHIC LOCATIONDE: 1635 Oceans;
- GLOBAL CHANGEDE: 4899 General or miscellaneous;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4999 General or miscellaneous;
- PALEOCEANOGRAPHY