A record of Neogene seawater δ11B reconstructed from paired δ11B analyses on benthic and planktic foraminifera

Greenop, Rosanna, Hain, Mathis P., Sosdian, Sindia M. ORCID: https://orcid.org/0000-0002-4599-5529, Oliver, Kevin I. C., Goodwin, Philip, Chalk, Thomas B., Lear, Caroline H. ORCID: https://orcid.org/0000-0002-7533-4430, Wilson, Paul A. and Foster, Gavin L. 2017. A record of Neogene seawater δ11B reconstructed from paired δ11B analyses on benthic and planktic foraminifera. Climate of the Past 13 , pp. 149-170. 10.5194/cp-13-149-2017

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Abstract

The boron isotope composition (δ11B) of foraminiferal calcite reflects the pH and the boron isotope composition of the seawater the foraminifer grew in. For pH reconstructions, the δ11B of seawater must therefore be known, but information on this parameter is limited. Here we reconstruct Neogene seawater δ11B based on the δ11B difference between paired measurements of planktic and benthic foraminifera and an estimate of the coeval water column pH gradient from their δ13C values. Carbon cycle model simulations underscore that the ΔpH–Δδ13C relationship is relatively insensitive to ocean and carbon cycle changes, validating our approach. Our reconstructions suggest that δ11Bsw was ∼ 37.5‰ during the early and middle Miocene (roughly 23–12Ma) and rapidly increased during the late Miocene (between 12 and 5 Ma) towards the modern value of 39.61‰. Strikingly, this pattern is similar to the evolution of the seawater isotope composition of Mg, Li and Ca, suggesting a common forcing mechanism. Based on the observed direction of change, we hypothesize that an increase in secondary mineral formation during continental weathering affected the isotope composition of riverine input to the ocean since 14Ma.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Earth and Environmental Sciences
Additional Information:	This paper is published under the terms of the CC-BY licence
Publisher:	European Geosciences Union (EGU) / Copernicus Publications
ISSN:	1814-9324
Date of First Compliant Deposit:	28 April 2016
Date of Acceptance:	9 January 2017
Last Modified:	05 May 2023 07:40
URI:	https://orca.cardiff.ac.uk/id/eprint/90082

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