The University of Southampton
University of Southampton Institutional Repository

Assessing the impact of diagenesis on d11B, d13C, d18O, Sr/Ca and B/Ca values in fossil planktic foraminiferal calcite

Assessing the impact of diagenesis on d11B, d13C, d18O, Sr/Ca and B/Ca values in fossil planktic foraminiferal calcite
Assessing the impact of diagenesis on d11B, d13C, d18O, Sr/Ca and B/Ca values in fossil planktic foraminiferal calcite
The geochemical composition of foraminiferal tests is a valuable archive for the reconstruction of paleo-climatic, -oceanographic and -ecological changes. However, dissolution of biogenic calcite and precipitation of inorganic calcite (overgrowth and recrystallization) at the seafloor and in the sediment column can potentially alter the original geochemical composition of the foraminiferal test, biasing any resulting paleoenvironmental reconstruction. The ?11B of planktic foraminiferal calcite is a promising ocean pH-proxy but the effect of diagenesis is still poorly known. Here we present new ?11B, ?13C, ?18O, Sr/Ca and B/Ca data from multiple species of planktic foraminifera from time-equivalent samples for two low latitude sites: clay-rich Tanzanian Drilling Project (TDP) Site 18 from the Indian Ocean containing well-preserved (‘glassy’) foraminifera and carbonate-rich Ocean Drilling Program (ODP) Site 865 from the central Pacific Ocean hosting recrystallized (‘frosty’) foraminifera. Our approach makes the assumption that environmental conditions were initially similar at both sites so most chemical differences are attributable to diagenesis. Planktic foraminiferal ?18O and ?13C records show offsets in both relative and absolute values between the two sites consistent with earlier findings that these isotopic ratios are strongly influenced by diagenetic alteration. Sr/Ca and B/Ca ratios in planktic foraminiferal calcite are also offset between the two sites but there is little change in the relative difference between surface and deep dwelling taxa. In contrast, ?11B values indicate no large differences between well-preserved and recrystallized foraminifera suggesting that despite extensive diagenetic alteration the ?11B of biogenic calcite appears robust, potentially indicative of a lack of free exchange of boron between pore fluids and the recrystallizing CaCO3. Our finding may remove one potential source of uncertainty in ?11B based pH reconstructions and provide us with greater confidence in our ability to reconstruct pH in the ancient oceans from at least some recrystallized foraminiferal calcite. However, further investigations should extend this approach to test the robustness of our findings across a range of taphonomies, ages and burial settings.
Diagenesis, Boron, ODP Site 865, Planktic foraminifera, Tanzanian Drilling Project, Ocean Drilling Program
0016-7037
180-209
Edgar, Kirsty M.
c180d215-e9ee-4a79-8274-a1e8a300c07c
Anagnostou, Eleni
4527c274-f765-44ce-89ab-0e437aa3d870
Pearson, Paul N.
76269a23-3411-45a1-bc81-b3a668ef1d13
Foster, Gavin L.
fbaa7255-7267-4443-a55e-e2a791213022
Edgar, Kirsty M.
c180d215-e9ee-4a79-8274-a1e8a300c07c
Anagnostou, Eleni
4527c274-f765-44ce-89ab-0e437aa3d870
Pearson, Paul N.
76269a23-3411-45a1-bc81-b3a668ef1d13
Foster, Gavin L.
fbaa7255-7267-4443-a55e-e2a791213022

Edgar, Kirsty M., Anagnostou, Eleni, Pearson, Paul N. and Foster, Gavin L. (2015) Assessing the impact of diagenesis on d11B, d13C, d18O, Sr/Ca and B/Ca values in fossil planktic foraminiferal calcite. Geochimica et Cosmochimica Acta, 166, 180-209.

Record type: Article

Abstract

The geochemical composition of foraminiferal tests is a valuable archive for the reconstruction of paleo-climatic, -oceanographic and -ecological changes. However, dissolution of biogenic calcite and precipitation of inorganic calcite (overgrowth and recrystallization) at the seafloor and in the sediment column can potentially alter the original geochemical composition of the foraminiferal test, biasing any resulting paleoenvironmental reconstruction. The ?11B of planktic foraminiferal calcite is a promising ocean pH-proxy but the effect of diagenesis is still poorly known. Here we present new ?11B, ?13C, ?18O, Sr/Ca and B/Ca data from multiple species of planktic foraminifera from time-equivalent samples for two low latitude sites: clay-rich Tanzanian Drilling Project (TDP) Site 18 from the Indian Ocean containing well-preserved (‘glassy’) foraminifera and carbonate-rich Ocean Drilling Program (ODP) Site 865 from the central Pacific Ocean hosting recrystallized (‘frosty’) foraminifera. Our approach makes the assumption that environmental conditions were initially similar at both sites so most chemical differences are attributable to diagenesis. Planktic foraminiferal ?18O and ?13C records show offsets in both relative and absolute values between the two sites consistent with earlier findings that these isotopic ratios are strongly influenced by diagenetic alteration. Sr/Ca and B/Ca ratios in planktic foraminiferal calcite are also offset between the two sites but there is little change in the relative difference between surface and deep dwelling taxa. In contrast, ?11B values indicate no large differences between well-preserved and recrystallized foraminifera suggesting that despite extensive diagenetic alteration the ?11B of biogenic calcite appears robust, potentially indicative of a lack of free exchange of boron between pore fluids and the recrystallizing CaCO3. Our finding may remove one potential source of uncertainty in ?11B based pH reconstructions and provide us with greater confidence in our ability to reconstruct pH in the ancient oceans from at least some recrystallized foraminiferal calcite. However, further investigations should extend this approach to test the robustness of our findings across a range of taphonomies, ages and burial settings.

PDF Edgar_Assessing.pdf - Accepted Manuscript
Download (24MB)
PDF 1-s2.0-S0016703715004019-main.pdf - Version of Record
Available under License Creative Commons Attribution.
Download (2MB)

More information

e-pub ahead of print date: 24 June 2015
Published date: 1 October 2015
Keywords: Diagenesis, Boron, ODP Site 865, Planktic foraminifera, Tanzanian Drilling Project, Ocean Drilling Program
Organisations: Geochemistry

Identifiers

Local EPrints ID: 378421
URI: https://eprints.soton.ac.uk/id/eprint/378421
ISSN: 0016-7037
PURE UUID: e9d45370-fd80-4c0a-9b01-935f872a8cec

Catalogue record

Date deposited: 26 Jun 2015 13:58
Last modified: 07 Nov 2017 22:25

Export record

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of https://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×