Preprints
https://doi.org/10.5194/egusphere-2024-3492
https://doi.org/10.5194/egusphere-2024-3492
21 Nov 2024
 | 21 Nov 2024
Status: this preprint is open for discussion.

Pelagic coccolithophore production and dissolution and their impacts on particulate inorganic carbon cycling in the western North Pacific

Yuye Han, Zvi Steiner, Zhimian Cao, Di Fan, Junhui Chen, Jimin Yu, and Minhan Dai

Abstract. Coccolithophores, a type of single-celled phytoplankton that is abundant in global oceans, are closely associated with the carbonate pump and thus play a crucial role in the marine carbon cycle. Here we investigated coccolithophore abundances, species compositions, coccolithophore calcium carbonate (CaCO3 as calcite) and particulate inorganic carbon (PIC) concentrations in the upper water column of the western North Pacific Ocean, along a meridional transect spanning the oligotrophic subtropical gyre and the nutrient-richer Kuroshio-Oyashio transition region. Our results revealed that Umbellosphaera tenuis was the dominant coccolithophore species in the former, while Emiliania huxleyi and Syracosphaera spp. dominated in the latter. Coccolithophore calcite contributed a major fraction of the PIC standing stocks above a depth of 150 m, among which E. huxleyi was the most important producer while less abundant and larger species also played a role. The coccolithophore CaCO3 production rate in the subtropical gyre (0.62 mol m−2 yr−1) was ~5-fold higher than that in the Kuroshio-Oyashio transition region (0.14 mol m−2 yr−1), indicating that inorganic carbon metabolism driven by coccolithophores is relatively strong in oligotrophic ocean waters. Using a box model including coccolithophore CaCO3 production and metabolic calcite saturation state, we demonstrated that CaCO3 dissolution associated with organic carbon metabolism can generate excess alkalinity in the oversaturated upper water column of the western North Pacific Ocean. Results of our study highlight the critical role of coccolithophores in CaCO3 production and dissolution; knowledge of these processes is important to assess PIC cycling and carbonate pump efficiency in the pelagic ocean.

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Yuye Han, Zvi Steiner, Zhimian Cao, Di Fan, Junhui Chen, Jimin Yu, and Minhan Dai

Status: open (until 02 Jan 2025)

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Yuye Han, Zvi Steiner, Zhimian Cao, Di Fan, Junhui Chen, Jimin Yu, and Minhan Dai
Yuye Han, Zvi Steiner, Zhimian Cao, Di Fan, Junhui Chen, Jimin Yu, and Minhan Dai

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Short summary
Coccolithophore calcite accounts for a major fraction of particulate inorganic carbon (PIC) standing stocks in the western North Pacific, with a markedly higher contribution in the oligotrophic subtropical gyre than in the Kuroshio-Oyashio transition region, which highlights the importance of coccolithophores for PIC production in the pelagic ocean. We also found extensive dissolution of coccolithophore calcite in the oversaturated shallow waters primarily driven by microbial metabolic activity.