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Assessing the impact of diagenesis on foraminiferal geochemistry from a low latitude, shallow-water drift deposit

Assessing the impact of diagenesis on foraminiferal geochemistry from a low latitude, shallow-water drift deposit
Assessing the impact of diagenesis on foraminiferal geochemistry from a low latitude, shallow-water drift deposit
Due to their large heat and moisture storage capabilities, the tropics are fundamental in modulating both regional and global climate. Furthermore, their thermal response during past extreme warming periods, such as super interglacials, is not fully resolved. In this regard, we present high-resolution (analytical) foraminiferal geochemical (O and Mg/Ca) records for the last 1800 kyr from the shallow (487 m) Inner Sea drift deposits of the Maldives archipelago in the equatorial Indian Ocean. Considering the diagenetic susceptibility of these proxies, in carbonate-rich environments, we assess the integrity of a suite of commonly used planktonic and benthic foraminifera geochemical datasets (Globigerinoides ruber (white), Globigerinita glutinata (with bulla), Pulleniatina obliquiloculata (with cortex) and Cibicides mabahethi) and their use for future paleoceanographic reconstructions.

Using a combination of spot Secondary Ion Mass Spectrometer, Electron Probe Micro-Analyzer and Scanning Electron Microscope image data, it is evident that authigenic overgrowths are present on both the external and internal test (shell) surfaces, yet the degree down-core as well as the associated bias is shown to be variable across the investigated species and proxies. Given the elevated authigenic overgrowth Mg/Ca (∼12–22 mmol/mol) and O values (closer to the benthic isotopic compositions) the whole-test planktonic G. ruber (w) geochemical records are notably impacted beyond ∼627.4 ka (24.7 mcd). Yet, considering the setting (i.e. bottom water location) for overgrowth formation, the benthic foraminifera O record is markedly less impacted with only minor diagenetic bias beyond ∼790.0 ka (28.7 mcd). Even though only the top of the G. ruber (w) and C. mabahethi records (whole-test data) would be suitable for paleo-reconstructions of absolute values (i.e. sea surface temperature, salinity, seawater O), the long-term cycles, while dampened, appear to be preserved. Furthermore, planktonic species with thicker-tests (i.e. P. obliquiloculata (w/c)) might be better suited, in comparison to thinner-test counter-parts (i.e. G. glutinata (w/b), G. ruber (w)), for traditional whole-test geochemical studies in shallow, carbonate-rich environments. A thicker test equates to a smaller overall bias from the authigenic overgrowth. Overall, if the diagenetic impact is constrained, as done in this study, these types of diagenetically altered geochemical records can still significantly contribute to studies relating to past tropical seawater temperatures, latitudinal scale ocean current shifts and South Asian Monsoon dynamics.
IODP, Mg/Ca, early diagenesis, foraminifera, stable isotopes, tropical drift deposits
0012-821X
Stainbank, Stephanie
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Spezzaferri, Silvia
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De Boever, Eva
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Bouvier, Anne-sophie
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Chilcott, Colin
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De Leau, Erica S.
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Foubert, Anneleen
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Kunkelova, Tereza
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Pichevin, Laetitia
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Raddatz, Jacek
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Rüggeberg, Andres
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Wright, James D.
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Yu, Siyao M.
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Zhang, Manlin
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Kroon, Dick
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Stainbank, Stephanie
096e5460-3d19-41b8-aa2a-1f264ff16302
Spezzaferri, Silvia
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De Boever, Eva
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Bouvier, Anne-sophie
cd599b4e-ef3a-417f-882f-ce00d5e89157
Chilcott, Colin
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De Leau, Erica S.
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Foubert, Anneleen
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Kunkelova, Tereza
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Pichevin, Laetitia
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Raddatz, Jacek
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Rüggeberg, Andres
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Wright, James D.
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Yu, Siyao M.
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Zhang, Manlin
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Kroon, Dick
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Stainbank, Stephanie, Spezzaferri, Silvia, De Boever, Eva, Bouvier, Anne-sophie, Chilcott, Colin, De Leau, Erica S., Foubert, Anneleen, Kunkelova, Tereza, Pichevin, Laetitia, Raddatz, Jacek, Rüggeberg, Andres, Wright, James D., Yu, Siyao M., Zhang, Manlin and Kroon, Dick (2020) Assessing the impact of diagenesis on foraminiferal geochemistry from a low latitude, shallow-water drift deposit. Earth and Planetary Science Letters, 545, [116390]. (doi:10.1016/j.epsl.2020.116390).

Record type: Article

Abstract

Due to their large heat and moisture storage capabilities, the tropics are fundamental in modulating both regional and global climate. Furthermore, their thermal response during past extreme warming periods, such as super interglacials, is not fully resolved. In this regard, we present high-resolution (analytical) foraminiferal geochemical (O and Mg/Ca) records for the last 1800 kyr from the shallow (487 m) Inner Sea drift deposits of the Maldives archipelago in the equatorial Indian Ocean. Considering the diagenetic susceptibility of these proxies, in carbonate-rich environments, we assess the integrity of a suite of commonly used planktonic and benthic foraminifera geochemical datasets (Globigerinoides ruber (white), Globigerinita glutinata (with bulla), Pulleniatina obliquiloculata (with cortex) and Cibicides mabahethi) and their use for future paleoceanographic reconstructions.

Using a combination of spot Secondary Ion Mass Spectrometer, Electron Probe Micro-Analyzer and Scanning Electron Microscope image data, it is evident that authigenic overgrowths are present on both the external and internal test (shell) surfaces, yet the degree down-core as well as the associated bias is shown to be variable across the investigated species and proxies. Given the elevated authigenic overgrowth Mg/Ca (∼12–22 mmol/mol) and O values (closer to the benthic isotopic compositions) the whole-test planktonic G. ruber (w) geochemical records are notably impacted beyond ∼627.4 ka (24.7 mcd). Yet, considering the setting (i.e. bottom water location) for overgrowth formation, the benthic foraminifera O record is markedly less impacted with only minor diagenetic bias beyond ∼790.0 ka (28.7 mcd). Even though only the top of the G. ruber (w) and C. mabahethi records (whole-test data) would be suitable for paleo-reconstructions of absolute values (i.e. sea surface temperature, salinity, seawater O), the long-term cycles, while dampened, appear to be preserved. Furthermore, planktonic species with thicker-tests (i.e. P. obliquiloculata (w/c)) might be better suited, in comparison to thinner-test counter-parts (i.e. G. glutinata (w/b), G. ruber (w)), for traditional whole-test geochemical studies in shallow, carbonate-rich environments. A thicker test equates to a smaller overall bias from the authigenic overgrowth. Overall, if the diagenetic impact is constrained, as done in this study, these types of diagenetically altered geochemical records can still significantly contribute to studies relating to past tropical seawater temperatures, latitudinal scale ocean current shifts and South Asian Monsoon dynamics.

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More information

Accepted/In Press date: 3 June 2020
e-pub ahead of print date: 23 June 2020
Published date: 1 September 2020
Keywords: IODP, Mg/Ca, early diagenesis, foraminifera, stable isotopes, tropical drift deposits

Identifiers

Local EPrints ID: 444803
URI: http://eprints.soton.ac.uk/id/eprint/444803
ISSN: 0012-821X
PURE UUID: 717e6bb0-dfa2-40c0-997f-f900d699b56c

Catalogue record

Date deposited: 05 Nov 2020 17:31
Last modified: 25 Nov 2021 19:37

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Contributors

Author: Stephanie Stainbank
Author: Silvia Spezzaferri
Author: Eva De Boever
Author: Anne-sophie Bouvier
Author: Colin Chilcott
Author: Erica S. De Leau
Author: Anneleen Foubert
Author: Laetitia Pichevin
Author: Jacek Raddatz
Author: Andres Rüggeberg
Author: James D. Wright
Author: Siyao M. Yu
Author: Manlin Zhang
Author: Dick Kroon

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