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Tropical Atlantic climate and ecosystem regime shifts during the Paleocene–Eocene Thermal Maximum

Tropical Atlantic climate and ecosystem regime shifts during the Paleocene–Eocene Thermal Maximum
Tropical Atlantic climate and ecosystem regime shifts during the Paleocene–Eocene Thermal Maximum
The Paleocene–Eocene Thermal Maximum (PETM, 56 Ma) was a phase of rapid global warming associated with massive carbon input into the ocean–atmosphere system from a 13C-depleted reservoir. Many midlatitude and high-latitude sections have been studied and document changes in salinity, hydrology and sedimentation, deoxygenation, biotic overturning, and migrations, but detailed records from tropical regions are lacking. Here, we study the PETM at Ocean Drilling Program (ODP) Site 959 in the equatorial Atlantic using a range of organic and inorganic proxies and couple these with dinoflagellate cyst (dinocyst) assemblage analysis. The PETM at Site 959 was previously found to be marked by a  ∼  3.8 ‰ negative carbon isotope excursion (CIE) and a  ∼  4 °C surface ocean warming from the uppermost Paleocene to peak PETM, of which  ∼  1 °C occurs before the onset of the CIE. We record upper Paleocene dinocyst assemblages that are similar to PETM assemblages as found in extratropical regions, confirming poleward migrations of ecosystems during the PETM. The early stages of the PETM are marked by a typical acme of the tropical genus Apectodinium, which reaches abundances of up to 95 %. Subsequently, dinocyst abundances diminish greatly, as do carbonate and pyritized silicate microfossils. The combined paleoenvironmental information from Site 959 and a close-by shelf site in Nigeria implies the general absence of eukaryotic surface-dwelling microplankton during peak PETM warmth in the eastern equatorial Atlantic, most likely caused by heat stress. We hypothesize, based on a literature survey, that heat stress might have reduced calcification in more tropical regions, potentially contributing to reduced deep sea carbonate accumulation rates, and, by buffering acidification, also to biological carbonate compensation of the injected carbon during the PETM. Crucially, abundant organic benthic foraminiferal linings imply sustained export production, likely driven by prokaryotes. In sharp contrast, the recovery of the CIE yields rapid (≪ 10 kyr) fluctuations in the abundance of several dinocyst groups, suggesting extreme ecosystem and environmental variability.
1814-9332
39-55
Frieling, Joost
76c2d878-65e9-4945-bc6b-1ab1daf7cb4d
Reichart, Gert-Jan
f56639e3-dd16-4dfc-941e-d55302ef9ee5
Middelburg, Jack J.
abdca8a9-843f-4940-afe1-81c4df84b913
Röhl, Ursula
c28c498d-f0a1-4c25-bf94-4bf46641ceed
Westerhold, Thomas
7b499943-ba7a-40e8-ae35-797594908d30
Bohaty, Steven M.
af9dbe78-8b9f-44f2-ba1d-20795837d2d1
Sluijs, Appy
af623507-b795-4458-8ca5-cce783869a3d
Frieling, Joost
76c2d878-65e9-4945-bc6b-1ab1daf7cb4d
Reichart, Gert-Jan
f56639e3-dd16-4dfc-941e-d55302ef9ee5
Middelburg, Jack J.
abdca8a9-843f-4940-afe1-81c4df84b913
Röhl, Ursula
c28c498d-f0a1-4c25-bf94-4bf46641ceed
Westerhold, Thomas
7b499943-ba7a-40e8-ae35-797594908d30
Bohaty, Steven M.
af9dbe78-8b9f-44f2-ba1d-20795837d2d1
Sluijs, Appy
af623507-b795-4458-8ca5-cce783869a3d

Frieling, Joost, Reichart, Gert-Jan, Middelburg, Jack J., Röhl, Ursula, Westerhold, Thomas, Bohaty, Steven M. and Sluijs, Appy (2018) Tropical Atlantic climate and ecosystem regime shifts during the Paleocene–Eocene Thermal Maximum. Climate of the Past, 14 (1), 39-55. (doi:10.5194/cp-14-39-2018).

Record type: Article

Abstract

The Paleocene–Eocene Thermal Maximum (PETM, 56 Ma) was a phase of rapid global warming associated with massive carbon input into the ocean–atmosphere system from a 13C-depleted reservoir. Many midlatitude and high-latitude sections have been studied and document changes in salinity, hydrology and sedimentation, deoxygenation, biotic overturning, and migrations, but detailed records from tropical regions are lacking. Here, we study the PETM at Ocean Drilling Program (ODP) Site 959 in the equatorial Atlantic using a range of organic and inorganic proxies and couple these with dinoflagellate cyst (dinocyst) assemblage analysis. The PETM at Site 959 was previously found to be marked by a  ∼  3.8 ‰ negative carbon isotope excursion (CIE) and a  ∼  4 °C surface ocean warming from the uppermost Paleocene to peak PETM, of which  ∼  1 °C occurs before the onset of the CIE. We record upper Paleocene dinocyst assemblages that are similar to PETM assemblages as found in extratropical regions, confirming poleward migrations of ecosystems during the PETM. The early stages of the PETM are marked by a typical acme of the tropical genus Apectodinium, which reaches abundances of up to 95 %. Subsequently, dinocyst abundances diminish greatly, as do carbonate and pyritized silicate microfossils. The combined paleoenvironmental information from Site 959 and a close-by shelf site in Nigeria implies the general absence of eukaryotic surface-dwelling microplankton during peak PETM warmth in the eastern equatorial Atlantic, most likely caused by heat stress. We hypothesize, based on a literature survey, that heat stress might have reduced calcification in more tropical regions, potentially contributing to reduced deep sea carbonate accumulation rates, and, by buffering acidification, also to biological carbonate compensation of the injected carbon during the PETM. Crucially, abundant organic benthic foraminiferal linings imply sustained export production, likely driven by prokaryotes. In sharp contrast, the recovery of the CIE yields rapid (≪ 10 kyr) fluctuations in the abundance of several dinocyst groups, suggesting extreme ecosystem and environmental variability.

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Accepted/In Press date: 13 November 2017
Published date: 15 January 2018

Identifiers

Local EPrints ID: 417601
URI: https://eprints.soton.ac.uk/id/eprint/417601
ISSN: 1814-9332
PURE UUID: d3c8ae45-22b1-402f-a024-745c88c6df57
ORCID for Steven M. Bohaty: ORCID iD orcid.org/0000-0002-1193-7398

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Date deposited: 07 Feb 2018 17:30
Last modified: 06 Jun 2018 12:39

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