eprintid: 1451023
rev_number: 29
eprint_status: archive
userid: 608
dir: disk0/01/45/10/23
datestamp: 2014-10-09 19:17:09
lastmod: 2021-09-20 22:22:14
status_changed: 2014-10-09 19:17:09
type: article
metadata_visibility: show
item_issues_count: 0
creators_name: Pogge von Strandmann, PAE
creators_name: Forshaw, J
creators_name: Schmidt, DN
title: Modern and Cenozoic records of seawater magnesium from foraminiferal Mg isotopes
ispublished: pub
divisions: UCL
divisions: B04
divisions: C06
divisions: F57
note: This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
abstract: Magnesium is an element critically involved in the carbon cycle, because weathering of Ca-Mg silicates removes atmospheric CO2 into rivers, and formation of Ca-Mg carbonates in the oceans removes carbon from the ocean-atmosphere system. Hence the Mg cycle holds the potential to provide valuable insights into Cenozoic climate-system history, and the shift during this time from a greenhouse to icehouse state. We present Mg isotope ratios for the past 40 Myr using planktic foraminifers as an archive. Modern foraminifera, which discriminate against elemental and isotopically heavy Mg during calcification, show no correlation between the Mg isotope composition (δ26Mg, relative to DSM-3) and temperature, Mg / Ca or other parameters such as carbonate saturation (ΔCO3). However, inter-species isotopic differences imply that only well-calibrated single species should be used for reconstruction of past seawater. Seawater δ26Mg inferred from the foraminiferal record decreased from ~0‰ at 15 Ma, to −0.83‰ at the present day, which coincides with increases in seawater lithium and oxygen isotope ratios. It strongly suggests that neither Mg concentrations nor isotope ratios are at steady state in modern oceans, given its ~10 Myr residence time. From these data, we have developed a dynamic box model to understand and constrain changes in Mg sources to the oceans (rivers) and Mg sinks (dolomitisation and hydrothermal alteration). Our estimates of seawater Mg concentrations through time are similar to those independently determined by pore waters and fluid inclusions. Modelling suggests that dolomite formation and the riverine Mg flux are the primary controls on the δ26Mg of seawater, while hydrothermal Mg removal and the δ26Mg of rivers are more minor controls. Using Mg riverine flux and isotope ratios inferred from the 87Sr / 86Sr record, the modelled Mg removal by dolomite formation shows minima in the Oligocene and at the present day (with decreasing trends from 15 Ma), both coinciding with rapid decreases in global temperatures.
date: 2014-09-25
official_url: http://dx.doi.org/10.5194/bg-11-5155-2014
vfaculties: VMPS
oa_status: green
full_text_type: pub
language: eng
primo: open
primo_central: open_green
verified: verified_manual
elements_source: crossref
elements_id: 984708
doi: 10.5194/bg-11-5155-2014
lyricists_name: Pogge Von Strandmann, Philip
lyricists_id: PPOGG57
full_text_status: public
publication: Biogeosciences
volume: 11
number: 18
pagerange: 5155 - 5168
issn: 1726-4170
citation:        Pogge von Strandmann, PAE;    Forshaw, J;    Schmidt, DN;      (2014)    Modern and Cenozoic records of seawater magnesium from foraminiferal Mg isotopes.                   Biogeosciences , 11  (18)   5155 - 5168.    10.5194/bg-11-5155-2014 <https://doi.org/10.5194/bg-11-5155-2014>.       Green open access   
 
document_url: https://discovery.ucl.ac.uk/id/eprint/1451023/1/bg-11-5155-2014.pdf