Impact of organic carbon reworking upon GDGT temperature proxies during the Paleocene-Eocene Thermal Maximum
Impact of organic carbon reworking upon GDGT temperature proxies during the Paleocene-Eocene Thermal Maximum
Glycerol dialkyl glycerol tetraethers (GDGTs) have been widely applied to coastal marine sediments to reconstruct past temperature variability. However, coastal environments are characterised by variability in the source, age and/or thermal maturity of different organic carbon (OC) pools and may bias various GDGT-based proxies. Here we analyse TEX86 and MBT5ME values within a shallow marine sediment core (South Dover Bridge, Maryland) from the Paleocene-Eocene Thermal Maximum (PETM; 56 million years ago (Ma)) to explore how changes in OC reworking influence GDGT-derived sea surface and terrestrial temperature estimates, respectively. We demonstrate that TEX86 values are unaffected by an increase in soil- and fossil organic carbon during the PETM. In contrast, we find large and unexpected variations in MBT5ME-derived temperature estimates (∼6 to 25 °C) during the onset and core of the PETM at some sites. This coincides with input of reworked terrestrial OC from the Cenomanian-aged Raritan Formation. However, there is also an increase in the degree of cyclisation of tetramethylated branched GDGTs, suggesting that branched GDGTs are also derived from marine in-situ production. These factors preclude terrestrial temperature reconstructions at this site. We explored whether OC reworking is problematic in other PETM-aged coastal environments. Using GDGT metrics and the Branched and Isoprenoid GDGT Machine learning Classification algorithm (BIGMaC), we demonstrate that TEX86 values are mostly unaffected by changes in OC sources. However, MBT5ME values are affected by marine and/or freshwater overprints, especially in environments with low terrestrial OC input. Taken together, this study highlights the importance of constraining the provenance of different GDGTs in marine and lacustrine environments.
Biomarkers, GDGTs, Hyperthermals, Reworking
Inglis, Gordon
1651196d-916c-43cb-b5a0-9b3ecaf5d664
Martinez-Sosa, Pablo
d423094f-0cbb-4245-852b-58cd87dcec9c
Tierney, Jessica E.
33ac78a0-f7c1-4bc6-bb6a-63e663414db2
Witkowski, Caitlyn
812a5fd8-863a-4659-bbf0-e805018099d4
Lyons, Shelby
5f8312e6-99dd-4155-90f0-1af8aebbbfaa
Baczynski, Allison
92426b31-1cb1-4422-b392-59be1c2884a7
Freeman, Katherine H.
d9200932-f523-44ed-a2de-da760d145ff0
September 2023
Inglis, Gordon
1651196d-916c-43cb-b5a0-9b3ecaf5d664
Martinez-Sosa, Pablo
d423094f-0cbb-4245-852b-58cd87dcec9c
Tierney, Jessica E.
33ac78a0-f7c1-4bc6-bb6a-63e663414db2
Witkowski, Caitlyn
812a5fd8-863a-4659-bbf0-e805018099d4
Lyons, Shelby
5f8312e6-99dd-4155-90f0-1af8aebbbfaa
Baczynski, Allison
92426b31-1cb1-4422-b392-59be1c2884a7
Freeman, Katherine H.
d9200932-f523-44ed-a2de-da760d145ff0
Inglis, Gordon, Martinez-Sosa, Pablo, Tierney, Jessica E., Witkowski, Caitlyn, Lyons, Shelby, Baczynski, Allison and Freeman, Katherine H.
(2023)
Impact of organic carbon reworking upon GDGT temperature proxies during the Paleocene-Eocene Thermal Maximum.
Organic Geochemistry, 183, [104644].
(doi:10.1016/j.orggeochem.2023.104644).
Abstract
Glycerol dialkyl glycerol tetraethers (GDGTs) have been widely applied to coastal marine sediments to reconstruct past temperature variability. However, coastal environments are characterised by variability in the source, age and/or thermal maturity of different organic carbon (OC) pools and may bias various GDGT-based proxies. Here we analyse TEX86 and MBT5ME values within a shallow marine sediment core (South Dover Bridge, Maryland) from the Paleocene-Eocene Thermal Maximum (PETM; 56 million years ago (Ma)) to explore how changes in OC reworking influence GDGT-derived sea surface and terrestrial temperature estimates, respectively. We demonstrate that TEX86 values are unaffected by an increase in soil- and fossil organic carbon during the PETM. In contrast, we find large and unexpected variations in MBT5ME-derived temperature estimates (∼6 to 25 °C) during the onset and core of the PETM at some sites. This coincides with input of reworked terrestrial OC from the Cenomanian-aged Raritan Formation. However, there is also an increase in the degree of cyclisation of tetramethylated branched GDGTs, suggesting that branched GDGTs are also derived from marine in-situ production. These factors preclude terrestrial temperature reconstructions at this site. We explored whether OC reworking is problematic in other PETM-aged coastal environments. Using GDGT metrics and the Branched and Isoprenoid GDGT Machine learning Classification algorithm (BIGMaC), we demonstrate that TEX86 values are mostly unaffected by changes in OC sources. However, MBT5ME values are affected by marine and/or freshwater overprints, especially in environments with low terrestrial OC input. Taken together, this study highlights the importance of constraining the provenance of different GDGTs in marine and lacustrine environments.
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Inglis 2023 accepted
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Accepted/In Press date: 12 July 2023
e-pub ahead of print date: 13 July 2023
Published date: September 2023
Additional Information:
Funding Information:
GNI is supported by a GCRF Royal Society Dorothy Hodgkin Fellowship (DHF\R1\191178) with additional support via the Royal Society (RF\ERE\231019, RF\ERE\210068). CRW is supported by Royal Society Dorothy Hodgkin Fellowship (DHF\R1\221014). We thank the National Environmental Isotope Facility (NEIF; No. NE/V003917/1) for analytical support. We acknowledge Jean Self-Trail (USGS) and the USGS Eastern Regional Drilling Crew who were influential in recovering the South Dover Bridge core. Finally, we thank Elizabeth Minor, the Associate Editor Courtney Turich, and two anonymous reviewers whose thoughtful comments significantly improved the manuscript.
Funding Information:
GNI is supported by a GCRF Royal Society Dorothy Hodgkin Fellowship (DHF\R1\191178) with additional support via the Royal Society (RF\ERE\231019, RF\ERE\210068). CRW is supported by Royal Society Dorothy Hodgkin Fellowship (DHF\R1\221014). We thank the National Environmental Isotope Facility (NEIF; No. NE/V003917/1) for analytical support. We acknowledge Jean Self-Trail (USGS) and the USGS Eastern Regional Drilling Crew who were influential in recovering the South Dover Bridge core. Finally, we thank Elizabeth Minor, the Associate Editor Courtney Turich, and two anonymous reviewers whose thoughtful comments significantly improved the manuscript.
Publisher Copyright:
© 2023 The Author(s)
Keywords:
Biomarkers, GDGTs, Hyperthermals, Reworking
Identifiers
Local EPrints ID: 480297
URI: http://eprints.soton.ac.uk/id/eprint/480297
ISSN: 0146-6380
PURE UUID: 70401416-dac5-4ee3-b86c-244df64d0891
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Date deposited: 01 Aug 2023 17:18
Last modified: 17 Mar 2024 04:00
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Contributors
Author:
Pablo Martinez-Sosa
Author:
Jessica E. Tierney
Author:
Caitlyn Witkowski
Author:
Shelby Lyons
Author:
Allison Baczynski
Author:
Katherine H. Freeman
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