Shoaling of the deep chlorophyll maximum during Early Eocene hyperthermals
Abstract
The Early Eocene Climate Optimum (EECO, 50-52 million years before present, Ma), known as the warmest long-standing period since 66 Ma, and its forgoing late Palaeocene-Eocene warming trend are punctuated by a series of orbitally-paced short-term global warming events, termed hyperthermals, of which the Palaeocene Thermal Maximum (PETM, 56 Ma) and Eocene Thermal Maximum 2 (ETM2, 54 Ma) are the most prominent. The increase in global temperatures during these hyperthermals are generally linked to greenhouse gas forcing, since numerous biological elements are elevated in isotopically light carbon, pointing to the addition of large amounts of CO2 and/or CH4 into the ocean and atmosphere systems. Here we present two high-resolution planktonic foraminiferal, e.g. Acarinina spp. and Subbotina spp., stable carbon isotope (d13C) records from ODP site 1263 portraying respectively surface water and thermocline conditions that encompass ETM2-EECO (49-54 Ma). We reconstructed carbon isotopic gradients between the surface and thermocline and between the thermocline and deep ocean waters, using the existing high-resolution benthic foraminiferal, e.g. Nuttallides truempyi, carbon isotope record derived from the same samples. Our results reveal a strong imprint of the short-term eccentricity ( 100 kyr) and obliquity ( 41 kyr) cycles on in particularly the thermocline-deep d13C gradient. Evidently, hyperthermals are characterized by a stronger thermocline-deep d13C gradient and a weaker surface-thermocline d13C gradient than their intermediary intervals. We interpret these systematic changes to a shoaling of the deep chlorophyll maximum due to enhanced stratified surface water conditions.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP21D1444L
- Keywords:
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- 0428 Carbon cycling;
- BIOGEOSCIENCESDE: 1616 Climate variability;
- GLOBAL CHANGEDE: 9604 Cenozoic;
- INFORMATION RELATED TO GEOLOGIC TIME