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Relationships Between Bottom Water Carbonate Saturation and Element/CA Ratios in Coretop Samples of the Benthic Foraminifera Oridorsalis Umbonatus : Volume 9, Issue 2 (02/02/2012)

By Dawber, C. F.

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Book Id: WPLBN0003981749
Format Type: PDF Article :
File Size: Pages 28
Reproduction Date: 2015

Title: Relationships Between Bottom Water Carbonate Saturation and Element/CA Ratios in Coretop Samples of the Benthic Foraminifera Oridorsalis Umbonatus : Volume 9, Issue 2 (02/02/2012)  
Author: Dawber, C. F.
Volume: Vol. 9, Issue 2
Language: English
Subject: Science, Biogeosciences, Discussions
Collections: Periodicals: Journal and Magazine Collection, Copernicus GmbH
Historic
Publication Date:
2012
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications

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Tripati, A., & Dawber, C. F. (2012). Relationships Between Bottom Water Carbonate Saturation and Element/CA Ratios in Coretop Samples of the Benthic Foraminifera Oridorsalis Umbonatus : Volume 9, Issue 2 (02/02/2012). Retrieved from http://www.ebooklibrary.org/


Description
Description: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB1 2EQ, UK. Elemental ratios in benthic foraminifera have been used to reconstruct bottom water temperature and carbonate saturation (Δ[CO32−]). We present elemental data for the long-ranging benthic foraminifera Oridorsalis umbonatus from sediment core tops that span a narrow range of temperatures and a wide range of saturation states. B/Ca, Li/Ca, Sr/Ca and Mg/Ca ratios exhibit positive correlations with bottom water carbonate saturation. The sensitivity of individual element/calcium ratios to bottom water Δ [CO32−] varies considerably, with B/Ca being most sensitive and Sr/Ca the least sensitive. The empirically derived sensitivity of B/Ca, Li/Ca, Mg/Ca and Sr/Ca to bottom water Δ [CO32−] are 0.433 ± 0.053 and 0.0561 ± 0.0084 μmol mol−1 per μmol kg−1 and 0.0164 ± 0.0015 and 0.00241 ± 0.0004 μmol mol−1 per μmol kg−1, respectively. To assess the fidelity of these relationships and the possibility of applying these relationships to earlier periods of Earth history, we examine the mechanisms governing elemental incorporation into foraminiferal calcite. Empirical partition coefficients for Li and Sr are consistent with Rayleigh fractionation from an internal pool used for calcification. For O. umbonatus and other benthic species, we show that the fraction of Ca remaining in the pool is a function of bottom water Δ [CO32−], and can be explained by either a growth rate effect and/or the energetic cost of raising vesicle pH at the site of calcification. Empirical partition coefficients for Mg and B may also be controlled by Rayleigh fractionation, but require that either the fractionation factor from the internal pool is smaller than the inorganic partition coefficient and/or additional fractionation mechanisms. O. umbonatus element ratio data may also be consistent with fractionation according to the surface entrapment model and/or the presence of discrete high- and low-Mg calcite phases. However at present we are limited in our ability to assess these mechanisms. The new X/Ca data for O. umbonatus provide constraints to test the role of these mechanisms in the future.

Summary
Relationships between bottom water carbonate saturation and element/Ca ratios in coretop samples of the benthic foraminifera Oridorsalis umbonatus

Excerpt
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