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Abstract

Roughly a third (~30 ppm) of the carbon dioxide (CO2) that entered the ocean during ice ages is attributed to biological mechanisms. A leading hypothesis for the biological drawdown of CO2 is iron (Fe) fertilisation of the high latitudes, but modelling efforts attribute at most 10 ppm to this mechanism, leaving ~20 ppm unexplained. We show that an Fe-induced stimulation of dinitrogen (N2) fixation can induce a low latitude drawdown of 7–16 ppm CO2. This mechanism involves a closer coupling between N2 fixers and denitrifiers that alleviates widespread nitrate limitation. Consequently, phosphate utilisation and carbon export increase near upwelling zones, causing deoxygenation and deeper carbon injection. Furthermore, this low latitude mechanism reproduces the regional patterns of organic δ15N deposited in glacial sediments. The positive response of marine N2 fixation to dusty ice age conditions, first proposed twenty years ago, therefore compliments high latitude changes to amplify CO2 drawdown.

Item Type:	Article
Authors/Creators:	Buchanan, PJ and Chase, Z and Matear, RJ and Phipps, SJ and Bindoff, NL
Keywords:	carbon dioxide, ocean, ice ages, iron, nitrogen
Journal or Publication Title:	Nature Communications
Publisher:	Nature Publishing Group
ISSN:	2041-1723
DOI / ID Number:	https://doi.org/10.1038/s41467-019-12549-z
Copyright Information:	Copyright 2019 The Authors. Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0) https://creativecommons.org/licenses/by/4.0/
Related URLs:	Google Scholar: Chase, Z UTAS Profile: Chase, Z Google Scholar: Phipps, SJ Google Scholar: Bindoff, NL UTAS Profile: Bindoff, NL
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