Simulated effect of calcification feedback on atmospheric CO2 and ocean acidification

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 and biogeochemical processes. Here, we detail the implementation of δ13C and δ15N in the ocean component of an Earth system model. We evaluate our simulated δ13C and δ15N against contemporary measurements, place the model's performance alongside other isotope-enabled models and document the response of δ13C and δ15N to changes in ecosystem functioning. The model combines the Commonwealth Scientific and Industrial Research Organisation Mark 3L (CSIRO Mk3L) climate system model with the Carbon of the Ocean, Atmosphere and Land (COAL) biogeochemical model. The oceanic component of CSIRO Mk3L-COAL has a resolution of 1.6∘ latitude × 2.8∘ longitude and resolves multimillennial timescales, running at a rate of ∼400 years per day. We show that this coarse-resolution, computationally efficient model adequately reproduces water column and core-top δ13C and δ15N measurements, making it a useful tool for palaeoceanographic research. Changes to ecosystem function involve varying phytoplankton stoichiometry, varying CaCO3 production based on calcite saturation state and varying N2 fixation via iron limitation. We find that large changes in CaCO3 production have little effect on δ13C and δ15N, while changes in N2 fixation and phytoplankton stoichiometry have substantial and complex effects. Interpretations of palaeoceanographic records are therefore open to multiple lines of interpretation where multiple processes imprint on the isotopic signature, such as in the tropics, where denitrification, N2 fixation and nutrient utilisation influence δ15N. Hence, there is significant scope for isotope-enabled models to provide more robust interpretations of the proxy records.

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“…The η coefficients were 0.53, 0.81 and 1.09. These numbers are equivalent to those in the experiments of Zhang and Cao (2016).…”

Section: Calcifier Dependence On Calcite Saturation Statementioning

confidence: 90%

“…The exponent (η) is easily modified consistent with the parameterisations of Zhang and Cao (2016) and controls the rate of CaCO 3 production at a given value of ca .…”

Section: A13 Calcifiersmentioning

confidence: 99%

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

et al. 2019

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“…Since alkalinity is the capacity of the ocean to buffer acids and sets the limit of how much CO 2 can be stored, changes in alkalinity have consequences for CO 2 storage. While the quantitative impact of the alkalinity pump on climate is currently unclear, its role via the "calcification feedback" on atmospheric CO 2 concentrations is assumed to be large (Zhang and Cao, 2016). Among the calcifiers, coccolithophores are the most important group (see, e.g., Rost and Riebesell, 2004) and mainly responsible for the vertical gradient in alkalinity.…”

Section: M1 -Biogeochemical Pumpsmentioning

confidence: 99%

Ideas and perspectives: climate-relevant marine biologically driven mechanisms in Earth system models

2017

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Abstract. The current generation of marine biogeochemical modules in Earth system models (ESMs) considers mainly the effect of marine biota on the carbon cycle. We propose to also implement other biologically driven mechanisms in ESMs so that more climate-relevant feedbacks are captured. We classify these mechanisms in three categories according to their functional role in the Earth system: (1) "biogeochemical pumps", which affect the carbon cycling; (2) "biological gas and particle shuttles", which affect the atmospheric composition; and (3) "biogeophysical mechanisms", which affect the thermal, optical, and mechanical properties of the ocean. To resolve mechanisms from all three classes, we find it sufficient to include five functional groups: bulk phyto-and zooplankton, calcifiers, and coastal gas and surface mat producers. We strongly suggest to account for a larger mechanism diversity in ESMs in the future to improve the quality of climate projections.

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“…The exponent (η) is easily modified consistent with the parameterisations of Zhang and Cao (2016) and controls the rate of CaCO 3 production at a given value of Ω ca .…”

Section: A13 Calcifiersmentioning

confidence: 99%

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

Buchanan¹,

Matear²,

Chase³

et al. 2018

Preprint

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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 and biogeochemical processes. Here, we detail the implementation of δ13C and δ15N in the ocean component of an Earth system model. We evaluate our simulated δ13C and δ15N against contemporary measurements, place the model's performance alongside other isotope enabled models, and document the response of δ13C and δ15N to changes in ecosystem functioning. The model combines the Commonwealth Scientific and Industrial Research Organisation Mark 3L (CSIRO Mk3L) climate system model with the Carbon of the Ocean, Atmosphere and Land (COAL) biogeochemical model. The oceanic component of CSIRO Mk3L-COAL has a resolution of 1.6° latitude × 2.8° longitude and resolves multi-millennial timescales, running at a rate of ∼400 years per day. We show that this coarse resolution, computationally efficient model adequately reproduces water column and coretop δ13C and δ15N measurements, making it a useful tool for palaeoceanographic research. Changes to ecosystem function involve varying phytoplankton stoichiometry, varying CaCO3 production based on calcite saturation state, and varying N2 fixation via iron limitation. We find that large changes in CaCO3 production have little effect on δ13C and δ15N, while changes in N2 fixation and phytoplankton stoichiometry have substantial and complex effects. Interpretations of palaeoceanographic records are therefore open to multiple lines of interpretation where multiple processes imprint on the isotopic signature, such as in the tropics where denitrification, N2 fixation and nutrient utilisation influence δ15N. Hence, there is significant scope for isotope enabled models to provide more robust interpretations of the proxy records.

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Simulated effect of calcification feedback on atmospheric CO2 and ocean acidification

Cited by 18 publications

References 41 publications

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

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

Ideas and perspectives: climate-relevant marine biologically driven mechanisms in Earth system models

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

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