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Reviews and syntheses: The biogeochemical cycle of silicon in the modern ocean Paul Tréguer, Jill Sutton, Mark Brzezinski, Matthew A. Charette, Timothy Devries, Stephanie Dutkiewicz, Claudia Ehlert, Jon Hawkings, Aude Leynaert, Su Mei Liu, et al. To cite this version: Paul Tréguer, Jill Sutton, Mark Brzezinski, Matthew A. Charette, Timothy Devries, et al.. Reviews and syntheses: The biogeochemical cycle of silicon in the modern ocean. Biogeosciences, European Geosciences Union, 2021, 18 (4), pp.1269–1289. 10.5194/bg-18-1269-2021. hal-03245525 HAL Id: hal-03245525 https://hal.archives-ouvertes.fr/hal-03245525 Submitted on 2 Jun 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution| 4.0 International License Biogeosciences, 18, 1269–1289, 2021 https://doi.org/10.5194/bg-18-1269-2021 © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License. Reviews and syntheses: The biogeochemical cycle of silicon in the modern ocean Paul J. Tréguer1,2, Jill N. Sutton1, Mark Brzezinski3, Matthew A. Charette4, Timothy Devries5, Stephanie Dutkiewicz6, Claudia Ehlert7, Jon Hawkings8,9, Aude Leynaert1, Su Mei Liu10,11, Natalia Llopis Monferrer1, María López-Acosta12,13, Manuel Maldonado13, Shaily Rahman14, Lihua Ran15, and Olivier Rouxel16 1Univ Brest, CNRS, IRD, Ifremer, Institut Universitaire Européen de la Mer, LEMAR, Rue Dumont d’Urville, 29280, Plouzané, France 2State Key Laboratory of Satellite Ocean Dynamics (SOED), Ministry of Natural Resource, Hangzhou 310012, China 3Marine Science Institute, University of California, Santa Barbara, CA, USA 4Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA 5Department of Geography, University of California, Santa Barbara, CA, USA 6Department of Earth, Atmospheric and Planetary Sciences (DEAPS), Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA 7Research Group for Marine Isotope Geochemistry, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany 8National High Magnetic Field Lab and Earth, Ocean and Atmospheric Sciences, Florida State University, Tallahassee, USA 9Interface Geochemistry, German Research Centre for Geosciences GFZ, Potsdam, Germany 10Frontiers Science Center for Deep Ocean Multispheres and Earth System, and Laboratory of Marine Chemistry Theory and Technology MOEy, Ocean University of China, Qingdao 266100, China 11Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China 12Institute of Marine Research (IIM-CSIC), Rúa de Eduardo Cabello 6, Vigo 36208, Pontevedra, Spain 13Department of Marine Ecology. Center for Advanced Studies of Blanes (CEAB-CSIC), Acceso Cala St. Francesc 14, Blanes 17300, Girona, Spain 14School of Ocean Science and Engineering, University of Southern Mississippi, Stennis Space Center, MS 39529, USA 15Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, P. R. China 16IFREMER, Centre de Brest, Technopôle Brest Iroise, Plouzané, France Correspondence: Paul Tréguer ([email protected]) and Jill Sutton ([email protected]) Received: 20 July 2020 – Discussion started: 3 August 2020 Revised: 18 December 2020 – Accepted: 23 December 2020 – Published: 18 February 2021 Abstract. The element silicon (Si) is required for the growth dicate that total Si inputs and outputs, to and from the world of silicified organisms in marine environments, such as di- ocean, are 57 % and 37 % higher, respectively, than previ- atoms. These organisms consume vast amounts of Si to- ous estimates. We also update the total ocean silicic acid in- gether with N, P, and C, connecting the biogeochemical cy- ventory value, which is about 24 % higher than previously cles of these elements. Thus, understanding the Si cycle in estimated. These changes are significant, modifying factors the ocean is critical for understanding wider issues such as such as the geochemical residence time of Si, which is now carbon sequestration by the ocean’s biological pump. In this about 8000 years, 2 times faster than previously assumed. review, we show that recent advances in process studies in- In addition, we present an updated value of the global an- Published by Copernicus Publications on behalf of the European Geosciences Union. 1270 P. J. Tréguer et al.: Reviews and syntheses: The biogeochemical cycle of silicon in the modern ocean nual pelagic biogenic silica production (255 Tmol Siyr−1) D 15:6.±2:4/ Tmol Siyr−1 (Fig. 1). Finally, we address the based on new data from 49 field studies and 18 model question of the potential impact of anthropogenic activities outputs, and we provide a first estimate of the global an- on the global Si cycle and suggest guidelines for future re- nual benthic biogenic silica production due to sponges search endeavors. (6 Tmol Siyr−1). Given these important modifications, we hypothesize that the modern ocean Si cycle is at approxi- mately steady state with inputs D 14:8.±2:6/ Tmol Siyr−1 2 Advances in input fluxes and outputs D 15:6.±2:4/ Tmol Siyr−1. Potential impacts of global change on the marine Si cycle are discussed. Silicic acid is delivered to the ocean through six pathways as illustrated in Fig. 1, which all ultimately derive from the weathering of the Earth’s crust (Tréguer and De La Rocha, 2013). All fluxes are given with an error of 1 standard devia- tion. 1 Introduction 2.1 Riverine (F ) and aeolian (F ) contributions Silicon, the seventh most abundant element in the universe, R A is the second most abundant element in the Earth’s crust. The best estimate for the riverine input (FR) of dSi, based The weathering of the Earth’s crust by CO2-rich rainwater, on data representing 60 % of the world river discharge a key process in the control of atmospheric CO2 (Berner et and a discharge-weighted average dSi riverine concentra- al., 1983; Wollast and Mackenzie, 1989), results in the gen- tion of 158 µM − Si (Dürr et al., 2011), remains at FRdSi D eration of silicic acid (dSi; Si.OH/4) in aqueous environ- 6:2.±1:8/ Tmol Siyr−1 (Tréguer and De La Rocha, 2013). ments. Silicifiers are among the most important aquatic or- However, not only dSi is transferred from the terrestrial to ganisms and include micro-organisms (e.g., diatoms, rhizar- the riverine system, with particulate Si mobilized in crys- ians, silicoflagellates, several species of choanoflagellates) tallized or amorphous forms (Dürr et al., 2011). Accord- and macro-organisms (e.g., siliceous sponges). Silicifiers use ing to Saccone et al. (2007), the term “amorphous silica” dSi to precipitate biogenic silica (bSi; SiO2) as internal (aSi) includes biogenic silica (bSi, from phytoliths, fresh- (Moriceau et al., 2019) and/or external (Maldonado et al., water diatoms, sponge spicules), altered bSi, and pedogenic 2019) structures. Phototrophic silicifiers, such as diatoms, silicates, the three of which can have similar high solubili- globally consume vast amounts of Si concomitantly with ni- ties and reactivities. Delivery of aSi to the fluvial system has trogen (N), phosphorus (P), and inorganic carbon (C), con- been reviewed by Frings et al. (2016), and they suggested necting the biogeochemistry of these elements and contribut- −1 a value of FRaSi D 1:9.±1:0/ Tmol Siyr . Therefore, total ing to the sequestration of atmospheric CO in the ocean −1 2 FR D 8:1.±2:0/ Tmol Siyr . (Tréguer and Pondaven, 2000). Heterotrophic organisms like No progress has been made regarding aeolian dust depo- rhizarians, choanoflagellates, and sponges produce bSi in- sition into the ocean (Tegen and Kohfeld, 2006) and subse- dependently of the photoautotrophic processing of C and quent release of dSi via dust dissolution in seawater since N (Maldonado et al., 2012, 2019; Llopis Monferrer et al., Tréguer and De La Rocha (2013), who summed the flux 2020). of particulate dissolvable silica and wet deposition of dSi Understanding the Si cycle is critical for understanding through precipitation. Thus, our best estimate for the aeolian the functioning of marine food webs, biogeochemical cy- −1 flux of dSi, FA, remains 0:5.±0:5/ Tmol Siyr . cles, and the biological carbon pump. Herein, we review re- cent advances in field observations and modeling that have 2.2 Dissolution of minerals (FW) changed our understanding of the global Si cycle and provide an update of four of the six net annual input fluxes and of all As shown in Fig. 2, the low-temperature dissolution of the output fluxes previously estimated by Tréguer and De La siliceous minerals in seawater and from sediments feeds a Rocha (2013). Taking into account numerous field studies in dSi flux, FW, through two processes: (1) the dissolution of different marine provinces and model outputs, we re-estimate river-derived lithogenic particles deposited along the conti- the Si production (Nelson et al., 1995), review the potential nental margins and shelves and (2) the dissolution of basaltic contribution of rhizarians (Llopis Monferrer et al., 2020) and glass in seawater, processes that work mostly in deep waters. picocyanobacteria (Ohnemus et al., 2016), and give an esti- About 15–20 Gtyr−1 of river-derived lithogenic particles are mate of the total bSi production by siliceous sponges using deposited along the margins and shelves (e.g., Syvitskia et recently published data on sponge bSi in marine sediments al., 2003; also see Fig. 2). Dissolution experiments with river (Maldonado et al., 2019).

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