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Ocean carbon and nitrogen isotopes in CSIRO Mk3L-COAL version 1.0: a tool for palaeoceanographic research

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Buchanan, PJ, Matear, RJ, Chase, Z ORCID: 0000-0001-5060-779X, Phipps, SJ ORCID: 0000-0001-5657-8782 and Bindoff, NL ORCID: 0000-0001-5662-9519 2019 , 'Ocean carbon and nitrogen isotopes in CSIRO Mk3L-COAL version 1.0: a tool for palaeoceanographic research' , Geoscientific Model Development, vol. 12, no. 4 , pp. 1491-1523 , doi: 10.5194/gmd-12-1491-2019.

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Abstract

The isotopes of carbon (δ13C) and nitrogen(δ15N) are commonly used proxies for understanding the ocean.When used in tandem, they provide powerful insight into physical andbiogeochemical processes. Here, we detail the implementation ofδ13C and δ15N in the ocean component of anEarth system model. We evaluate our simulated δ13C andδ15N against contemporary measurements, place the model'sperformance alongside other isotope-enabled models and document the responseof δ13C and δ15N to changes in ecosystemfunctioning. The model combines the Commonwealth Scientific and IndustrialResearch Organisation Mark 3L (CSIRO Mk3L) climate system model with theCarbon of the Ocean, Atmosphere and Land (COAL) biogeochemical model. Theoceanic component of CSIRO Mk3L-COAL has a resolution of 1.6∘latitude × 2.8∘ longitude and resolves multimillennialtimescales, running at a rate of ∼400 years per day. We show that thiscoarse-resolution, computationally efficient model adequately reproduceswater column and core-top δ13C and δ15Nmeasurements, making it a useful tool for palaeoceanographic research.Changes to ecosystem function involve varying phytoplankton stoichiometry,varying CaCO3 production based on calcite saturation state andvarying N2 fixation via iron limitation. We find that large changesin CaCO3 production have little effect on δ13C andδ15N, while changes in N2 fixation and phytoplanktonstoichiometry have substantial and complex effects. Interpretations ofpalaeoceanographic records are therefore open to multiple lines ofinterpretation where multiple processes imprint on the isotopic signature,such as in the tropics, where denitrification, N2 fixation andnutrient utilisation influence δ15N. Hence, there issignificant scope for isotope-enabled models to provide more robustinterpretations of the proxy records.

Item Type: Article
Authors/Creators:Buchanan, PJ and Matear, RJ and Chase, Z and Phipps, SJ and Bindoff, NL
Keywords: palaeoclimate, palaeoceanography, climate models, ocean models, isotopes, carbon, nitrogen
Journal or Publication Title: Geoscientific Model Development
Publisher: Copernicus GmbH
ISSN: 1991-959X
DOI / ID Number: 10.5194/gmd-12-1491-2019
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/

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