Dynamic Biological Functioning Important for Simulating and Stabilizing Ocean Biogeochemistry

Buchanan, Pearse; Matear, Richard J.; Chase, Zanna; Phipps, Steven J.; Bindoff, Nathaniel L.

doi:10.1002/2017gb005753

Cited by 15 publications

(18 citation statements)

References 137 publications

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“…This type of non-Redfieldian dynamics was applied in the model used in Eggleston and Galbraith (2018) and Galbraith and de Lavergne (2018), but their results were not analysed in terms of difference from a Redfield model version. In addition, Buchanan et al (2018) explored the importance of dynamic response of ocean biology, such as flexible stoichiometry, for modelled ocean biogeochemistry in pre-industrial simulations. They found that the dynamic response was fundamental for stabilizing the response of ocean dissolved inorganic carbon (DIC) to changes in the physical circulation state.…”

Section: Introductionmentioning

confidence: 99%

Variable C∕P composition of organic production and its effect on ocean carbon storage in glacial-like model simulations

et al. 2020

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Abstract. During the four most recent glacial maxima, atmospheric CO2 has been lowered by about 90–100 ppm with respect to interglacial concentrations. It is likely that most of the atmospheric CO2 deficit was stored in the ocean. Changes in the biological pump, which are related to the efficiency of the biological carbon uptake in the surface ocean and/or of the export of organic carbon to the deep ocean, have been proposed as a key mechanism for the increased glacial oceanic CO2 storage. The biological pump is strongly constrained by the amount of available surface nutrients. In models, it is generally assumed that the ratio between elemental nutrients, such as phosphorus, and carbon (C∕P ratio) in organic material is fixed according to the classical Redfield ratio. The constant Redfield ratio appears to approximately hold when averaged over basin scales, but observations document highly variable C∕P ratios on regional scales and between species. If the C∕P ratio increases when phosphate availability is scarce, as observations suggest, this has the potential to further increase glacial oceanic CO2 storage in response to changes in surface nutrient distributions. In the present study, we perform a sensitivity study to test how a phosphate-concentration-dependent C∕P ratio influences the oceanic CO2 storage in an Earth system model of intermediate complexity (cGENIE). We carry out simulations of glacial-like changes in albedo, radiative forcing, wind-forced circulation, remineralization depth of organic matter, and mineral dust deposition. Specifically, we compare model versions with the classical constant Redfield ratio and an observationally motivated variable C∕P ratio, in which the carbon uptake increases with decreasing phosphate concentration. While a flexible C∕P ratio does not impact the model's ability to simulate benthic δ13C patterns seen in observational data, our results indicate that, in production of organic matter, flexible C∕P can further increase the oceanic storage of CO2 in glacial model simulations. Past and future changes in the C∕P ratio thus have implications for correctly projecting changes in oceanic carbon storage in glacial-to-interglacial transitions as well as in the present context of increasing atmospheric CO2 concentrations.

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Section: Introductionmentioning

confidence: 99%

Variable C∕P composition of organic production and its effect on ocean carbon storage in glacial-like model simulations

et al. 2020

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“…For example phosphate concentrations are systematically overestimated in the surface (Martiny et al, 2019a) and the global distribution of nitrogen fixation, denitrification, and oxygen minimum zones exhibit substantial variability between models (Fu et al, 2018). Recent global biogeochemical models are therefore starting to incorporate a more realistic representation of plankton physiology, which includes flexible phytoplankton C:N:P (e.g., Buchanan et al, 2018). Modeling studies with flexible phytoplankton stoichiometry have demonstrated that proliferation of C-rich phytoplankton under future climate scenario has the potential to buffer expected future decline in carbon export and net primary productivity caused by increased stratification (Kwiatkowski et al, 2018;Tanioka and Matsumoto, 2017).…”

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confidence: 99%

A meta-analysis on environmental drivers of marine phytoplankton C : N : P

Tanioka¹,

Matsumoto²

2019

Preprint

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Abstract. The elemental stoichiometry of marine phytoplankton plays a critical role in the global carbon cycle through carbon export. Although extensive laboratory experiments have been carried out over the years to assess the influence of different environmental drivers on the elemental composition of phytoplankton, a comprehensive quantitative assessment of the processes is still lacking. Here, we synthesized the responses of P : C and N : C ratios of marine phytoplankton to five major drivers (phosphate and nitrate, irradiance, temperature, and iron) by meta-analysis of laboratory experimental data available in the literature. Our results show that the response of the ratios to changes in macronutrients is consistent across all the studies, where the nutrient availability is positively related to changes in P : C and N : C ratios. We found that diatoms are more sensitive to the changes in macronutrients compared to other eukaryotes and cyanobacteria, possibly due to their larger cell size and their abilities to quickly regulate their gene expression patterns required for nutrient uptake. The effect of irradiance on P : C was mixed and not significant, but the same effect on N : C was significant and constant across all studies where an increase in irradiance decreased N : C. The response to temperature changes was mixed by species, except warming consistently decreased P : C ratio in cyanobacteria. This may explain why P : C is consistently low in the cyanobacteria-dominated subtropical oceans. The effect of iron on P : C and N : C for cyanobacteria were statistically significant but the small sample size precludes drawing firm conclusions. Overall, our findings highlight the high stoichiometric plasticity of diatoms and the importance of macronutrients in determining P : C and N : C ratios, which both provide us insights on how to understand and model plankton diversity and productivity.

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“…CSIRO Mk3L-COAL adequately reproduces the large-scale thermohaline properties and circulation of the ocean under preindustrial conditions in numerous prior studies (Phipps et al, 2013;Matear and Lenton, 2014;Buchanan et al, 2016Buchanan et al, , 2018.…”

Section: Model Performancementioning

confidence: 76%

“…evaporation). Because fractionation against one isotope relative to the other is miniscule, the isotopic content of a sample is conventionally expressed as a δ value (δ h E), where the ratio of the heavy to light element in solution ( h E: l E) is compared to a standard ratio ( h E std : l E std ) Previous versions of the OBGCM have explored changes in oceanic properties under past (Buchanan et al, 2016), present (Buchanan et al, 2018) and future scenarios Lenton, 2014, 2018). These studies have shown that the model can realistically reproduce the global carbon cycle, nutrient cycling and organic matter cycling in the ocean.…”

Section: Introductionmentioning

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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Dynamic Biological Functioning Important for Simulating and Stabilizing Ocean Biogeochemistry

Cited by 15 publications

References 137 publications

Variable C∕P composition of organic production and its effect on ocean carbon storage in glacial-like model simulations

Variable C∕P composition of organic production and its effect on ocean carbon storage in glacial-like model simulations

A meta-analysis on environmental drivers of marine phytoplankton C : N : P

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

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