A probabilistic assessment of calcium carbonate export and dissolution in the modern ocean

Battaglia, Gianna; Steinacher, Marco; Joos, Fortunat (2016). A probabilistic assessment of calcium carbonate export and dissolution in the modern ocean. Biogeosciences, 13(9), pp. 2823-2848. Copernicus Publications 10.5194/bg-13-2823-2016

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The marine cycle of calcium carbonate (CaCO3) is an important element of the carbon cycle and co-governs the distribution of carbon and alkalinity within the ocean. However, CaCO3 export fluxes and mechanisms governing CaCO3 dissolution are highly uncertain. We present an observationally constrained, probabilistic assessment of the global and regional CaCO3 budgets. Parameters governing pelagic CaCO3 export fluxes and dissolution rates are sampled using a Monte Carlo scheme to construct a 1000-member ensemble with the Bern3D ocean model. Ensemble results are constrained by comparing simulated and observation-based fields of excess dissolved calcium carbonate (TA*). The minerals calcite and aragonite are modelled explicitly and ocean–sediment fluxes are considered. For local dissolution rates, either a strong or a weak dependency on CaCO3 saturation is assumed. In addition, there is the option to have saturation-independent dissolution above the saturation horizon. The median (and 68 % confidence interval) of the constrained model ensemble for global biogenic CaCO3 export is 0.90 (0.72–1.05) Gt C yr−1, that is within the lower half of previously published estimates (0.4–1.8 Gt C yr−1). The spatial pattern of CaCO3 export is broadly consistent with earlier assessments. Export is large in the Southern Ocean, the tropical Indo–Pacific, the northern Pacific and relatively small in the Atlantic. The constrained results are robust across a range of diapycnal mixing coefficients and, thus, ocean circulation strengths. Modelled ocean circulation and transport timescales for the different set-ups were further evaluated with CFC11 and radiocarbon observations. Parameters and mechanisms governing dissolution are hardly constrained by either the TA* data or the current compilation of CaCO3 flux measurements such that model realisations with and without saturation-dependent dissolution achieve skill. We suggest applying saturation-independent dissolution rates in Earth system models to minimise computational costs.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Climate and Environmental Physics
10 Strategic Research Centers > Oeschger Centre for Climate Change Research (OCCR)

Graduate School:

Graduate School of Climate Sciences

UniBE Contributor:

Battaglia, Gianna; Steinacher, Marco and Joos, Fortunat

Subjects:

500 Science > 530 Physics
500 Science > 550 Earth sciences & geology

ISSN:

1726-4170

Publisher:

Copernicus Publications

Language:

English

Submitter:

Doris Rätz

Date Deposited:

06 Jul 2016 09:35

Last Modified:

06 Jul 2016 09:43

Publisher DOI:

10.5194/bg-13-2823-2016

BORIS DOI:

10.7892/boris.82526

URI:

https://boris.unibe.ch/id/eprint/82526

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