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Influence of test size, water depth, and ecology on Mg/Ca, Sr/Ca,δ18O and δ13C in nine modern species of planktic foraminifers

Influence of test size, water depth, and ecology on Mg/Ca, Sr/Ca,δ18O and δ13C in nine modern species of planktic foraminifers
Influence of test size, water depth, and ecology on Mg/Ca, Sr/Ca,δ18O and δ13C in nine modern species of planktic foraminifers
Mg/Ca palaeothermometry in foraminiferal calcite is a widely applied tool in palaeoceanography. However, our understanding of the effects of planktic foraminiferal ecology and early diagenesis on test calcite Mg/Ca is limited. Here we report results of a study designed to shed new light on ecological, size-related and very early (water column) diagenetic controls on Mg/Ca in planktic foraminiferal calcite. We analysed Mg/Ca and stable isotopes of nine modern planktic foraminiferal species across fourteen mostly 50 μm-window sieve fractions in a core-top sample from the North Atlantic Ocean. We also analysed Mg/Ca in four of these nine species from plankton-tow samples collected from 0 to 2500 m water depth in the North Atlantic Ocean and Arabian Sea. Our core-top study confirms that sensitivity of Mg/Ca to change in test size is species-specific but reveals an overall decrease in Mg/Ca with increasing test size in all but one species, Orbulina universa, for which Mg/Ca increases with size. These findings are broadly consistent with known ecological behaviour suggesting that the size-related signal is largely environmentally rather than calcification-rate controlled. Our results underscore the need to undertake Mg/Ca palaeothermometry on narrow size fractions of planktic foraminifers, particularly for shallow-dwelling species such as G. bulloides and G. ruber where Mg/Ca is most sensitive to test size across the size range of 200–350 μm. Our plankton-tow data from the Arabian Sea are in agreement with in-situ temperatures.
In contrast, our data from the North Atlantic Ocean reveal large variability and marked offsets (to warmer values) from in-situ temperatures that are interpreted to reflect lateral advection from the south, storm-induced vertical mixing of the water column and/or the influence of surface-water salinity on the Mg/Ca signal. None of our plankton-tow Mg/Ca data shows any evidence of test dissolution in the water column. Our study provides important verification that the Mg/Ca signal recorded during calcification does not undergo diagenetic degradation during test transport to the sea floor, thereby satisfying an important precondition of its palaeo-proxy utility.
Mg/Ca, planktic foraminifera, ecology, dissolution, core-top, plankton tow
0012-821X
133-145
Friedrich, Oliver
30dc21d4-6581-4b89-96b1-c11689e85078
Schiebel, Ralf
eb56bd42-3b0a-44bd-8d21-d50786263986
Wilson, Paul
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Weldeab, Syee
c1bb0462-e3ac-4664-b898-c5bea023fb7a
Beer, Christopher
c00378b9-7f32-4782-a8ef-2cb03c72701f
Cooper, Matthew
54f7bff0-1f8c-4835-8358-71eef8529e7a
Fiebig, Jens
2002fcc6-8c97-4f72-9f07-76efa9bd89ee
Friedrich, Oliver
30dc21d4-6581-4b89-96b1-c11689e85078
Schiebel, Ralf
eb56bd42-3b0a-44bd-8d21-d50786263986
Wilson, Paul
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Weldeab, Syee
c1bb0462-e3ac-4664-b898-c5bea023fb7a
Beer, Christopher
c00378b9-7f32-4782-a8ef-2cb03c72701f
Cooper, Matthew
54f7bff0-1f8c-4835-8358-71eef8529e7a
Fiebig, Jens
2002fcc6-8c97-4f72-9f07-76efa9bd89ee

Friedrich, Oliver, Schiebel, Ralf, Wilson, Paul, Weldeab, Syee, Beer, Christopher, Cooper, Matthew and Fiebig, Jens (2012) Influence of test size, water depth, and ecology on Mg/Ca, Sr/Ca,δ18O and δ13C in nine modern species of planktic foraminifers. Earth and Planetary Science Letters, 319-320 (2), 133-145. (doi:10.1016/j.epsl.2011.12.002).

Record type: Article

Abstract

Mg/Ca palaeothermometry in foraminiferal calcite is a widely applied tool in palaeoceanography. However, our understanding of the effects of planktic foraminiferal ecology and early diagenesis on test calcite Mg/Ca is limited. Here we report results of a study designed to shed new light on ecological, size-related and very early (water column) diagenetic controls on Mg/Ca in planktic foraminiferal calcite. We analysed Mg/Ca and stable isotopes of nine modern planktic foraminiferal species across fourteen mostly 50 μm-window sieve fractions in a core-top sample from the North Atlantic Ocean. We also analysed Mg/Ca in four of these nine species from plankton-tow samples collected from 0 to 2500 m water depth in the North Atlantic Ocean and Arabian Sea. Our core-top study confirms that sensitivity of Mg/Ca to change in test size is species-specific but reveals an overall decrease in Mg/Ca with increasing test size in all but one species, Orbulina universa, for which Mg/Ca increases with size. These findings are broadly consistent with known ecological behaviour suggesting that the size-related signal is largely environmentally rather than calcification-rate controlled. Our results underscore the need to undertake Mg/Ca palaeothermometry on narrow size fractions of planktic foraminifers, particularly for shallow-dwelling species such as G. bulloides and G. ruber where Mg/Ca is most sensitive to test size across the size range of 200–350 μm. Our plankton-tow data from the Arabian Sea are in agreement with in-situ temperatures.
In contrast, our data from the North Atlantic Ocean reveal large variability and marked offsets (to warmer values) from in-situ temperatures that are interpreted to reflect lateral advection from the south, storm-induced vertical mixing of the water column and/or the influence of surface-water salinity on the Mg/Ca signal. None of our plankton-tow Mg/Ca data shows any evidence of test dissolution in the water column. Our study provides important verification that the Mg/Ca signal recorded during calcification does not undergo diagenetic degradation during test transport to the sea floor, thereby satisfying an important precondition of its palaeo-proxy utility.

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More information

Accepted/In Press date: 1 December 2011
e-pub ahead of print date: 20 January 2012
Published date: 15 February 2012
Additional Information: Copyright © 2011 Elsevier B.V. All rights reserved.
Keywords: Mg/Ca, planktic foraminifera, ecology, dissolution, core-top, plankton tow
Organisations: Geochemistry, Paleooceanography & Palaeoclimate

Identifiers

Local EPrints ID: 338021
URI: http://eprints.soton.ac.uk/id/eprint/338021
ISSN: 0012-821X
PURE UUID: 845f4176-1768-4c89-9d2a-55d47ce910d3
ORCID for Paul Wilson: ORCID iD orcid.org/0000-0001-6425-8906
ORCID for Matthew Cooper: ORCID iD orcid.org/0000-0002-2130-2759

Catalogue record

Date deposited: 08 May 2012 13:36
Last modified: 15 Mar 2024 03:09

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Contributors

Author: Oliver Friedrich
Author: Ralf Schiebel
Author: Paul Wilson ORCID iD
Author: Syee Weldeab
Author: Christopher Beer
Author: Matthew Cooper ORCID iD
Author: Jens Fiebig

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