Articles | Volume 12, issue 4
https://doi.org/10.5194/bg-12-1007-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
the Creative Commons Attribution 3.0 License.
Special issue:
https://doi.org/10.5194/bg-12-1007-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
the Creative Commons Attribution 3.0 License.
Research article
| 
17 Feb 2015
Research article |
| 17 Feb 2015
The relative importance of phytoplankton aggregates and zooplankton fecal pellets to carbon export: insights from free-drifting sediment trap deployments in naturally iron-fertilised waters near the Kerguelen Plateau
E. C. Laurenceau-Cornec
CORRESPONDING AUTHOR
CSIRO-UTAS Quantitative Marine Sciences PhD Program, Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart TAS 7001, Australia
Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Private Bag 80, Hobart TAS 7001, Australia
T. W. Trull
Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Private Bag 80, Hobart TAS 7001, Australia
Commonwealth Scientific and Industrial Research Organisation, Marine and Atmospheric Research, Castray Esplanade, Hobart TAS 7000, Australia
D. M. Davies
Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Private Bag 80, Hobart TAS 7001, Australia
S. G. Bray
Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Private Bag 80, Hobart TAS 7001, Australia
J. Doran
UWA Oceans Institute, The University of Western Australia (M470), 35 Stirling Highway, Crawley WA 6009, Australia
F. Planchon
Laboratoire des Sciences de l'Environnement Marin (LEMAR), Université de Brest, CNRS, IRD, UMR6539, IUEM, Technopôle Brest Iroise, Place Nicolas Copernic, 29280 Plouzané, France
F. Carlotti
Mediterranean Institute of Oceanography (MIO), Aix-Marseille Université, CNRS-IRD, 13288 Marseille, CEDEX 09, France
M.-P. Jouandet
Mediterranean Institute of Oceanography (MIO), Aix-Marseille Université, CNRS-IRD, 13288 Marseille, CEDEX 09, France
A.-J. Cavagna
Vrije Universiteit Brussel, Analytical and Environmental Geochemistry Dept., Brussels, Belgium
A. M. Waite
UWA Oceans Institute, The University of Western Australia (M470), 35 Stirling Highway, Crawley WA 6009, Australia
Alfred Wegener Institute Helmholz Centre for Polar and Marine Research, Building E-2155, Am Handelshafen 12, 27570 Bremerhaven, Germany
S. Blain
Sorbonne Universités, UPMC Univ. Paris 06, UMR 7621, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, 66650 Banyuls/mer, France
CNRS, UMR 7621, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, 66650 Banyuls/mer, France
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François Carlotti, Marc Pagano, Loïc Guilloux, Katty Donoso, Valentina Valdés, Olivier Grosso, and Brian P. V. Hunt
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Géraldine Sarthou, Pascale Lherminier, Eric P. Achterberg, Fernando Alonso-Pérez, Eva Bucciarelli, Julia Boutorh, Vincent Bouvier, Edward A. Boyle, Pierre Branellec, Lidia I. Carracedo, Nuria Casacuberta, Maxi Castrillejo, Marie Cheize, Leonardo Contreira Pereira, Daniel Cossa, Nathalie Daniault, Emmanuel De Saint-Léger, Frank Dehairs, Feifei Deng, Floriane Desprez de Gésincourt, Jérémy Devesa, Lorna Foliot, Debany Fonseca-Batista, Morgane Gallinari, Maribel I. García-Ibáñez, Arthur Gourain, Emilie Grossteffan, Michel Hamon, Lars Eric Heimbürger, Gideon M. Henderson, Catherine Jeandel, Catherine Kermabon, François Lacan, Philippe Le Bot, Manon Le Goff, Emilie Le Roy, Alison Lefèbvre, Stéphane Leizour, Nolwenn Lemaitre, Pere Masqué, Olivier Ménage, Jan-Lukas Menzel Barraqueta, Herlé Mercier, Fabien Perault, Fiz F. Pérez, Hélène F. Planquette, Frédéric Planchon, Arnout Roukaerts, Virginie Sanial, Raphaëlle Sauzède, Catherine Schmechtig, Rachel U. Shelley, Gillian Stewart, Jill N. Sutton, Yi Tang, Nadine Tisnérat-Laborde, Manon Tonnard, Paul Tréguer, Pieter van Beek, Cheryl M. Zurbrick, and Patricia Zunino
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Nolwenn Lemaitre, Frédéric Planchon, Hélène Planquette, Frank Dehairs, Debany Fonseca-Batista, Arnout Roukaerts, Florian Deman, Yi Tang, Clarisse Mariez, and Géraldine Sarthou
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We investigated the surface particulate organic carbon export fluxes in the North Atlantic with the objective of better understanding the biological carbon pump. Our results highlighted that exports depended on the intensity and stage of the bloom, the phytoplankton size and community structures. After comparing with primary production, we concluded that, during our study, the North Atlantic behaves like most of the highly productive areas in the world's ocean, with a low export efficiency.
Valentina Valdés, François Carlotti, Ruben Escribano, Katty Donoso, Marc Pagano, Verónica Molina, and Camila Fernandez
Biogeosciences, 15, 6019–6032, https://doi.org/10.5194/bg-15-6019-2018, https://doi.org/10.5194/bg-15-6019-2018, 2018
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The role of N and P released by copepods on biogeochemical cycles and the microbial community during the OUTPACE cruise was studied. In the presence of copepods, NH4+ and DON increase, and an enhanced remineralization was observed. A shift in active bacterial composition was observed, linked with changes in nutrient concentrations. Copepods can be a source of (in)organic compounds for bacterial communities that contribute to nutrient recycling and regenerated production in the photic zone.
Mathieu Rembauville, Stéphane Blain, Clara Manno, Geraint Tarling, Anu Thompson, George Wolff, and Ian Salter
Biogeosciences, 15, 3071–3084, https://doi.org/10.5194/bg-15-3071-2018, https://doi.org/10.5194/bg-15-3071-2018, 2018
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Sinking phytoplankton from the surface ocean provide the principal energy source to deep-ocean ecosystems. Our aim was to understand how different phytoplankton communities impact the chemical nature of this sinking material. We show certain types of phytoplankton can preferentially export energy-rich storage compounds to the seafloor. Any climate-driven effects on phytoplankton community structure could thus impact remote deep-ocean ecosystems thousands of kilometres beneath the surface.
Nolwenn Lemaitre, Hélène Planquette, Frédéric Planchon, Géraldine Sarthou, Stéphanie Jacquet, Maribel I. García-Ibáñez, Arthur Gourain, Marie Cheize, Laurence Monin, Luc André, Priya Laha, Herman Terryn, and Frank Dehairs
Biogeosciences, 15, 2289–2307, https://doi.org/10.5194/bg-15-2289-2018, https://doi.org/10.5194/bg-15-2289-2018, 2018
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We present the particulate biogenic barium distributions in the North Atlantic for the first time with the objective of estimating mesopelagic carbon remineralisation fluxes. The remineralisation fluxes balanced or slightly exceeded the upper-ocean carbon export fluxes. This is a key result as the North Atlantic is generally assumed to be efficient in transferring carbon to the deep ocean, but during our study, the North Atlantic was characterized by a near-zero carbon sequestration efficiency.
Andrés S. Rigual Hernández, José A. Flores, Francisco J. Sierro, Miguel A. Fuertes, Lluïsa Cros, and Thomas W. Trull
Biogeosciences, 15, 1843–1862, https://doi.org/10.5194/bg-15-1843-2018, https://doi.org/10.5194/bg-15-1843-2018, 2018
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Long-term and annual field observations on key organisms are a critical basis for predicting changes in Southern Ocean ecosystems. Coccolithophores are the most abundant calcium-carbonate-producing phytoplankton and play an important role in Southern Ocean biogeochemical cycles. In this study we document the composition, degree of calcification and annual cycle of coccolithophore communities in one of the largest unexplored regions of the world oceans: the Antarctic zone.
Thomas W. Trull, Abraham Passmore, Diana M. Davies, Tim Smit, Kate Berry, and Bronte Tilbrook
Biogeosciences, 15, 31–49, https://doi.org/10.5194/bg-15-31-2018, https://doi.org/10.5194/bg-15-31-2018, 2018
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We present the first large-scale survey of planktonic biogenic carbonate concentrations south of Australia, accompanied by biogenic silica and particulate organic carbon. These suggest that coccolithophores are largely restricted to subantarctic waters and are present in much lower abundance than in Northern Hemisphere polar waters. Comparison to upper ocean properties suggests that thermal tolerance and competition with diatoms for limiting iron may be as influential as ocean acidification.
Paula Conde Pardo, Bronte Tilbrook, Clothilde Langlais, Thomas William Trull, and Stephen Rich Rintoul
Biogeosciences, 14, 5217–5237, https://doi.org/10.5194/bg-14-5217-2017, https://doi.org/10.5194/bg-14-5217-2017, 2017
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The carbon content of the water masses of the Southern Ocean south of Tasmania has increased over the period 1995–2011, leading to a general decrease in pH. An enhancement in the upwelling of DIC-rich deep waters is the main plausible cause of the increase in carbon in surface waters south of the Polar Front. North of the Polar Front, strong winds favor the ventilation of surface to intermediate layers, where the DIC increase is explained by the uptake of atmospheric CO2.
Ivia Closset, Damien Cardinal, Mathieu Rembauville, François Thil, and Stéphane Blain
Biogeosciences, 13, 6049–6066, https://doi.org/10.5194/bg-13-6049-2016, https://doi.org/10.5194/bg-13-6049-2016, 2016
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Isotopic measurements were used to investigate the seasonal evolution of the silicon (Si) biogeochemical cycle in a naturally iron-fertilized area of the Southern Ocean. When comparing data from early spring and summer periods, the relationship between Si depletion, biogenic silica production, and their isotopic composition appears decoupled in this region. Considering these results, we refined the seasonal net Si production that was mainly sustained by surface phytoplankton populations.
A. J. Cavagna, F. Fripiat, M. Elskens, P. Mangion, L. Chirurgien, I. Closset, M. Lasbleiz, L. Florez-Leiva, D. Cardinal, K. Leblanc, C. Fernandez, D. Lefèvre, L. Oriol, S. Blain, B. Quéguiner, and F. Dehairs
Biogeosciences, 12, 6515–6528, https://doi.org/10.5194/bg-12-6515-2015, https://doi.org/10.5194/bg-12-6515-2015, 2015
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Primary production, NO3- and NH4+ uptake, and nitrification rates were measured during the KEOPS 2 cruise (austral spring 2011) in the Kerguelen Plateau area. Natural iron fertilization stimulated primary production which is much higher in the fertilized areas compared to the HNLC site. We report high rates of nitrification in the mixed layer below the euphotic zone. We conclude that high productivity in deep mixing system stimulates the N cycle by increasing both assimilation and regeneration.
M. N. Müller, J. Barcelos e Ramos, K. G. Schulz, U. Riebesell, J. Kaźmierczak, F. Gallo, L. Mackinder, Y. Li, P. N. Nesterenko, T. W. Trull, and G. M. Hallegraeff
Biogeosciences, 12, 6493–6501, https://doi.org/10.5194/bg-12-6493-2015, https://doi.org/10.5194/bg-12-6493-2015, 2015
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The White Cliffs of Dover date back to the Cretaceous and are made up of microscopic chalky shells which were produced mainly by marine phytoplankton (coccolithophores). This is iconic proof for their success at times of relatively high seawater calcium concentrations and, as shown here, to be linked to their ability to precipitate calcium as chalk. The invention of calcification can thus be considered an evolutionary milestone allowing coccolithophores to thrive at times when others struggled.
F. d'Ovidio, A. Della Penna, T. W. Trull, F. Nencioli, M.-I. Pujol, M.-H. Rio, Y.-H. Park, C. Cotté, M. Zhou, and S. Blain
Biogeosciences, 12, 5567–5581, https://doi.org/10.5194/bg-12-5567-2015, https://doi.org/10.5194/bg-12-5567-2015, 2015
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Field campaigns are instrumental in providing ground truth for understanding and modeling global ocean biogeochemical budgets. A survey however can only inspect a fraction of the global oceans, typically a region hundreds of kilometers wide for a temporal window of the order of (at most) several weeks. In this spatiotemporal domain, mesoscale variability can mask climatological contrasts. Here we propose the use of multisatellite-based Lagrangian diagnostics to solve this issue.
A. S. Rigual-Hernández, T. W. Trull, S. G. Bray, A. Cortina, and L. K. Armand
Biogeosciences, 12, 5309–5337, https://doi.org/10.5194/bg-12-5309-2015, https://doi.org/10.5194/bg-12-5309-2015, 2015
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Diatom and major components of the flux collected by two sediment traps in subantarctic and polar frontal zones were studied. Despite significant differences in the composition and magnitude of the flux, POC flux was similar between sites. The development of a group of bloom-forming diatoms during summer led to the formation of aggregates and enhanced POC export. Our results suggest that high biogenic silica accumulation rates should be interpreted as a proxy for iron-limited diatom assemblages.
F. Carlotti, M.-P. Jouandet, A. Nowaczyk, M. Harmelin-Vivien, D. Lefèvre, P. Richard, Y. Zhu, and M. Zhou
Biogeosciences, 12, 4543–4563, https://doi.org/10.5194/bg-12-4543-2015, https://doi.org/10.5194/bg-12-4543-2015, 2015
A. R. Bowie, P. van der Merwe, F. Quéroué, T. Trull, M. Fourquez, F. Planchon, G. Sarthou, F. Chever, A. T. Townsend, I. Obernosterer, J.-B. Sallée, and S. Blain
Biogeosciences, 12, 4421–4445, https://doi.org/10.5194/bg-12-4421-2015, https://doi.org/10.5194/bg-12-4421-2015, 2015
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Iron biogeochemical budgets during the natural ocean fertilisation experiment KEOPS-2 showed that complex circulation and transport pathways were responsible for differences in the mode and strength of iron supply, with vertical supply dominant on the plateau and lateral supply dominant in the plume. The exchange of iron between dissolved, biogenic and lithogenic pools was highly dynamic, resulting in a decoupling of iron supply and carbon export and controlling the efficiency of fertilization.
F. Quéroué, G. Sarthou, H. F. Planquette, E. Bucciarelli, F. Chever, P. van der Merwe, D. Lannuzel, A. T. Townsend, M. Cheize, S. Blain, F. d'Ovidio, and A. R. Bowie
Biogeosciences, 12, 3869–3883, https://doi.org/10.5194/bg-12-3869-2015, https://doi.org/10.5194/bg-12-3869-2015, 2015
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Dissolved Fe (dFe) concentrations were measured in the vicinity of the Kerguelen Islands. Direct island runoff, glacial melting, and resuspended sediments were identified as important inputs of dFe that could potentially fertilise the northern part of the plateau. Overall, heterogeneous sources of Fe over and off the plateau, in addition to strong variability in Fe supply by vertical or horizontal transport, may explain the high variability in dFe concentrations observed during this study.
F. Planchon, D. Ballas, A.-J. Cavagna, A. R. Bowie, D. Davies, T. Trull, E. C. Laurenceau-Cornec, P. Van Der Merwe, and F. Dehairs
Biogeosciences, 12, 3831–3848, https://doi.org/10.5194/bg-12-3831-2015, https://doi.org/10.5194/bg-12-3831-2015, 2015
M. Rembauville, I. Salter, N. Leblond, A. Gueneugues, and S. Blain
Biogeosciences, 12, 3153–3170, https://doi.org/10.5194/bg-12-3153-2015, https://doi.org/10.5194/bg-12-3153-2015, 2015
M. Rembauville, S. Blain, L. Armand, B. Quéguiner, and I. Salter
Biogeosciences, 12, 3171–3195, https://doi.org/10.5194/bg-12-3171-2015, https://doi.org/10.5194/bg-12-3171-2015, 2015
M. Grenier, A. Della Penna, and T. W. Trull
Biogeosciences, 12, 2707–2735, https://doi.org/10.5194/bg-12-2707-2015, https://doi.org/10.5194/bg-12-2707-2015, 2015
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Four bio-profilers were deployed in the high-biomass plume downstream of the Kerguelen Plateau (KP; Southern Ocean) to examine the conditions favouring phytoplankton accumulation. Regions of very high Chla accumulation were mainly associated with surface waters from the northern KP. Light limitation seems to have a limited influence on production. A cyclonic eddy was associated with a significant export of organic matter and a subsequent dissolved inorganic carbon storage in the ocean interior.
I. Obernosterer, M. Fourquez, and S. Blain
Biogeosciences, 12, 1983–1992, https://doi.org/10.5194/bg-12-1983-2015, https://doi.org/10.5194/bg-12-1983-2015, 2015
M. Fourquez, I. Obernosterer, D. M. Davies, T. W. Trull, and S. Blain
Biogeosciences, 12, 1893–1906, https://doi.org/10.5194/bg-12-1893-2015, https://doi.org/10.5194/bg-12-1893-2015, 2015
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In this manuscript, we present the results of iron uptake measured in the naturally iron-fertilized area during the Kerguelen Ocean and Plateau compared Study 2 cruise (KEOPS2). Iron uptake by bulk community and several size fractions (microplankton, pico-nanoplankton and bacteria) are presented, compared and discussed in the present paper. This work also presents first investigations on the potential competition between bacteria and phytoplankton for access to iron.
S. H. M. Jacquet, F. Dehairs, D. Lefèvre, A. J. Cavagna, F. Planchon, U. Christaki, L. Monin, L. André, I. Closset, and D. Cardinal
Biogeosciences, 12, 1713–1731, https://doi.org/10.5194/bg-12-1713-2015, https://doi.org/10.5194/bg-12-1713-2015, 2015
F. Dehairs, F. Fripiat, A.-J. Cavagna, T. W. Trull, C. Fernandez, D. Davies, A. Roukaerts, D. Fonseca Batista, F. Planchon, and M. Elskens
Biogeosciences, 12, 1459–1482, https://doi.org/10.5194/bg-12-1459-2015, https://doi.org/10.5194/bg-12-1459-2015, 2015
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We investigated the nitrate N, O isotopic composition for the Southern Ocean Kerguelen Plateau area, aiming at understanding the N-cycling in this naturally iron fertilized area characterized by large recurrent phytoplankton blooms. The system is characterized by moderate consumption of nitrate over the season while silicic acid, on the contrary, becomes depleted, suggesting significant recycling of N. Mixed layer nitrate isotopic signatures corroborate this.
V. Sanial, P. van Beek, B. Lansard, M. Souhaut, E. Kestenare, F. d'Ovidio, M. Zhou, and S. Blain
Biogeosciences, 12, 1415–1430, https://doi.org/10.5194/bg-12-1415-2015, https://doi.org/10.5194/bg-12-1415-2015, 2015
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We investigated the origin and mechanisms of the natural iron fertilization that sustains a phytoplankton bloom downstream of the Kerguelen Islands. We used radium isotopes to trace the fate of shelf waters that may transport iron and other micronutrients towards offshore waters. We show that shelf waters are rapidly transferred offshore and may be transported across the polar front (PF). The PF may thus not be a strong physical barrier for chemical elements released by the shelf sediments.
T. W. Trull, D. M. Davies, F. Dehairs, A.-J. Cavagna, M. Lasbleiz, E. C. Laurenceau-Cornec, F. d'Ovidio, F. Planchon, K. Leblanc, B. Quéguiner, and S. Blain
Biogeosciences, 12, 1029–1056, https://doi.org/10.5194/bg-12-1029-2015, https://doi.org/10.5194/bg-12-1029-2015, 2015
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The KEOPS2 oceanographic study surveyed more than 30 sites downstream from the Kerguelen Islands in the Southern Ocean to examine the degree of variation in phytoplankton community responses to natural iron inputs. Our observations of community structure based on the chemical compositions of six microbial size fractions suggest that early spring trophodynamic and export responses differed between regions with persistently low levels versus punctually high levels of iron fertilisation.
P. van der Merwe, A. R. Bowie, F. Quéroué, L. Armand, S. Blain, F. Chever, D. Davies, F. Dehairs, F. Planchon, G. Sarthou, A. T. Townsend, and T. W. Trull
Biogeosciences, 12, 739–755, https://doi.org/10.5194/bg-12-739-2015, https://doi.org/10.5194/bg-12-739-2015, 2015
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Trace metal analysis of suspended and settling particles and underlying sediment was undertaken to elucidate the source to sink progression of the particulate trace metal pool near Kerguelen Island (Southern Ocean). Findings indicate that the Kerguelen Plateau is a source of trace metals via resuspended shelf sediments, especially below the mixed layer. However, glacial/fluvial runoff into shallow coastal waters is an important mode of fertilisation to areas downstream of Kerguelen Island.
S. Blain, J. Capparos, A. Guéneuguès, I. Obernosterer, and L. Oriol
Biogeosciences, 12, 623–635, https://doi.org/10.5194/bg-12-623-2015, https://doi.org/10.5194/bg-12-623-2015, 2015
M. L. González, V. Molina, L. Florez-Leiva, L. Oriol, A. J. Cavagna, F. Dehairs, L. Farias, and C. Fernandez
Biogeosciences Discuss., https://doi.org/10.5194/bgd-11-17151-2014, https://doi.org/10.5194/bgd-11-17151-2014, 2014
Revised manuscript not accepted
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This study shows for first time N2 fixation is occurring in the HNLC area of Southern Ocean and in naturally iron-fertilized waters, at rates exceeding previous reports for high latitudes (up to 20.11 nmol N L-1 d-1). Diazotrophs were identified as heterotrophic bacterioplankton; with an indirect role of dFe in the regulation of this process. Fertilization enhancing regenerated primary production may control N2 fixation via the availability od DOM for heterotrophic bacterioplankton.
U. Christaki, D. Lefèvre, C. Georges, J. Colombet, P. Catala, C. Courties, T. Sime-Ngando, S. Blain, and I. Obernosterer
Biogeosciences, 11, 6739–6753, https://doi.org/10.5194/bg-11-6739-2014, https://doi.org/10.5194/bg-11-6739-2014, 2014
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The concurrent investigation of several parameters has provided insight into two key roles of heterotrophic bacteria, and the microbial food web functioning, at the onset and late phase of the spring phytoplankton bloom induced by natural iron fertilization in the Southern Ocean.
M. Lasbleiz, K. Leblanc, S. Blain, J. Ras, V. Cornet-Barthaux, S. Hélias Nunige, and B. Quéguiner
Biogeosciences, 11, 5931–5955, https://doi.org/10.5194/bg-11-5931-2014, https://doi.org/10.5194/bg-11-5931-2014, 2014
I. Closset, M. Lasbleiz, K. Leblanc, B. Quéguiner, A.-J. Cavagna, M. Elskens, J. Navez, and D. Cardinal
Biogeosciences, 11, 5827–5846, https://doi.org/10.5194/bg-11-5827-2014, https://doi.org/10.5194/bg-11-5827-2014, 2014
M.-P. Jouandet, G. A. Jackson, F. Carlotti, M. Picheral, L. Stemmann, and S. Blain
Biogeosciences, 11, 4393–4406, https://doi.org/10.5194/bg-11-4393-2014, https://doi.org/10.5194/bg-11-4393-2014, 2014
M. Zhou, Y. Zhu, F. d'Ovidio, Y.-H. Park, I. Durand, E. Kestenare, V. Sanial, P. Van-Beek, B. Queguiner, F. Carlotti, and S. Blain
Biogeosciences Discuss., https://doi.org/10.5194/bgd-11-6845-2014, https://doi.org/10.5194/bgd-11-6845-2014, 2014
Revised manuscript has not been submitted
F. A. C. Le Moigne, M. Gallinari, E. Laurenceau, and C. L. De La Rocha
Biogeosciences, 10, 5755–5765, https://doi.org/10.5194/bg-10-5755-2013, https://doi.org/10.5194/bg-10-5755-2013, 2013
C. Guinet, X. Xing, E. Walker, P. Monestiez, S. Marchand, B. Picard, T. Jaud, M. Authier, C. Cotté, A. C. Dragon, E. Diamond, D. Antoine, P. Lovell, S. Blain, F. D'Ortenzio, and H. Claustre
Earth Syst. Sci. Data, 5, 15–29, https://doi.org/10.5194/essd-5-15-2013, https://doi.org/10.5194/essd-5-15-2013, 2013
Related subject area
Biogeochemistry: Open Ocean
A time series analysis of transparent exopolymer particle distributions and C : N stoichiometry in the subtropical North Pacific: a key process in net community production and preformed nitrate anomalies?
Marine snow morphology drives sinking and attenuation in the ocean interior
An upper-mesopelagic-zone carbon budget for the subarctic North Pacific
Ocean alkalinity enhancement in an open-ocean ecosystem: biogeochemical responses and carbon storage durability
Relationships between the concentration of particulate organic nitrogen and the inherent optical properties of seawater in oceanic surface waters
Inadequacies in the representation of sub-seasonal phytoplankton dynamics in Earth system models
Nitrogen dynamics and nitrate stable isotopes indicate nitrogen loss in the Bay of Bengal
A tracer study for the development of in-water monitoring, reporting, and verification (MRV) of ship-based ocean alkalinity enhancement
Composite model-based estimate of the ocean carbon sink from 1959 to 2022
Phytoplankton community structure in relation to iron and macronutrient fluxes from subsurface waters in the western North Pacific during summer
Intense and localized export of selected marine snow types at eddy edges in the South Atlantic Ocean
Spatial distributions of iron and manganese in surface waters of the Arctic's Laptev and East Siberian seas
Climate-driven shifts in Southern Ocean primary producers and biogeochemistry in CMIP6 models
Oceanic enrichment of ammonium and its impacts on phytoplankton community composition under a high-emissions scenario
Ocean acidification trends and carbonate system dynamics across the North Atlantic subpolar gyre water masses during 2009–2019
Pelagic coccolithophore production and dissolution and their impacts on particulate inorganic carbon cycling in the western North Pacific
From small scale variability to mesoscale stability in surface ocean pH: implications for air-sea CO2 equilibration
Sedimentary organic matter signature hints at the phytoplankton-driven biological carbon pump in the central Arabian Sea
Hydrological cycle amplification imposes spatial patterns on the climate change response of ocean pH and carbonate chemistry
Assessing the tropical Atlantic biogeochemical processes in the Norwegian Earth System Model
Evolution of oxygen and stratification and their relationship in the North Pacific Ocean in CMIP6 Earth system models
Evaluation of CMIP6 model performance in simulating historical biogeochemistry across the southern South China Sea
Drivers of decadal trends in the ocean carbon sink in the past, present, and future in Earth system models
Anthropogenic carbon storage and its decadal changes in the Atlantic between 1990–2020
Ocean alkalinity enhancement impacts: regrowth of marine microalgae in alkaline mineral concentrations simulating the initial concentrations after ship-based dispersions
Climatic controls on metabolic constraints in the ocean
Effects of grain size and seawater salinity on magnesium hydroxide dissolution and secondary calcium carbonate precipitation kinetics: implications for ocean alkalinity enhancement
Short-term response of Emiliania huxleyi growth and morphology to abrupt salinity stress
Assessing the impact of CO2-equilibrated ocean alkalinity enhancement on microbial metabolic rates in an oligotrophic system
Phosphomonoesterase and phosphodiesterase activities in the eastern Mediterranean in two contrasting seasonal situations
Net primary production annual maxima in the North Atlantic projected to shift in the 21st century
Testing the influence of light on nitrite cycling in the eastern tropical North Pacific
Loss of nitrogen via anaerobic ammonium oxidation (anammox) in the California Current system during the late Quaternary
Technical note: Assessment of float pH data quality control methods – a case study in the subpolar northwest Atlantic Ocean
Linking northeastern North Pacific oxygen changes to upstream surface outcrop variations
Underestimation of multi-decadal global O2 loss due to an optimal interpolation method
Reviews and syntheses: expanding the global coverage of gross primary production and net community production measurements using Biogeochemical-Argo floats
Characteristics of surface physical and biogeochemical parameters within mesoscale eddies in the Southern Ocean
Seasonal dynamics and annual budget of dissolved inorganic carbon in the northwestern Mediterranean deep-convection region
The fingerprint of climate variability on the surface ocean cycling of iron and its isotopes
Reconstructing the ocean's mesopelagic zone carbon budget: sensitivity and estimation of parameters associated with prokaryotic remineralization
Seasonal cycles of biogeochemical fluxes in the Scotia Sea, Southern Ocean: a stable isotope approach
Absence of photophysiological response to iron addition in autumn phytoplankton in the Antarctic sea-ice zone
Optimal parameters for the ocean's nutrient, carbon, and oxygen cycles compensate for circulation biases but replumb the biological pump
Importance of multiple sources of iron for the upper-ocean biogeochemistry over the northern Indian Ocean
Exploring the role of different data types and timescales in the quality of marine biogeochemical model calibration
All about nitrite: exploring nitrite sources and sinks in the eastern tropical North Pacific oxygen minimum zone
Fossil coccolith morphological attributes as a new proxy for deep ocean carbonate chemistry
Reconstructing ocean carbon storage with CMIP6 Earth system models and synthetic Argo observations
Using machine learning and Biogeochemical-Argo (BGC-Argo) floats to assess biogeochemical models and optimize observing system design
Kieran Curran, Tracy A. Villareal, and Robert T. Letscher
Biogeosciences, 22, 3515–3531, https://doi.org/10.5194/bg-22-3515-2025, https://doi.org/10.5194/bg-22-3515-2025, 2025
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This work provides a 2-year record of marine organic gel concentrations from an open-ocean site in the subtropical North Pacific Ocean north of Hawaii. These microscopic gels are investigated to understand their importance as an understudied component of organic matter cycling by marine microbes. We find an important role of gel cycling during the summer months, helping explain previously contradictory estimates of nutrient supply and demand for the subtropical ocean.
Yawouvi Dodji Soviadan, Miriam Beck, Joelle Habib, Alberto Baudena, Laetitia Drago, Alexandre Accardo, Remi Laxenaire, Sabrina Speich, Peter Brandt, Rainer Kiko, and Stemmann Lars
Biogeosciences, 22, 3485–3501, https://doi.org/10.5194/bg-22-3485-2025, https://doi.org/10.5194/bg-22-3485-2025, 2025
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Key parameters representing the gravity flux in global models are sinking speed and vertical attenuation of exported material. We calculate, for the first time, these parameters in situ in the ocean for six intermittent blooms followed by export events using high-resolution (3 d) time series of 0–1000 m depth profiles from imaging sensors mounted on an Argo float. We show that sinking speed depends not only on size but also on the morphology of the particles, with density being an important property.
Brandon M. Stephens, Montserrat Roca-Martí, Amy E. Maas, Vinícius J. Amaral, Samantha Clevenger, Shawnee Traylor, Claudia R. Benitez-Nelson, Philip W. Boyd, Ken O. Buesseler, Craig A. Carlson, Nicolas Cassar, Margaret Estapa, Andrea J. Fassbender, Yibin Huang, Phoebe J. Lam, Olivier Marchal, Susanne Menden-Deuer, Nicola L. Paul, Alyson E. Santoro, David A. Siegel, and David P. Nicholson
Biogeosciences, 22, 3301–3328, https://doi.org/10.5194/bg-22-3301-2025, https://doi.org/10.5194/bg-22-3301-2025, 2025
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The ocean’s mesopelagic zone (MZ) plays a crucial role in the global carbon cycle. This study combines new and previously published measurements of organic carbon supply and demand collected in August 2018 in the MZ of the subarctic North Pacific Ocean. Supply was insufficient to meet demand in August, but supply entering into the MZ in the spring of 2018 could have met the August demand. Results suggest observations over seasonal timescales may help to close MZ carbon budgets.
Allanah Joy Paul, Mathias Haunost, Silvan Urs Goldenberg, Jens Hartmann, Nicolás Sánchez, Julieta Schneider, Niels Suitner, and Ulf Riebesell
Biogeosciences, 22, 2749–2766, https://doi.org/10.5194/bg-22-2749-2025, https://doi.org/10.5194/bg-22-2749-2025, 2025
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Ocean alkalinity enhancement (OAE) is being assessed for its potential to absorb atmospheric CO2 and store it for a long time. OAE still needs comprehensive assessment of its safety and effectiveness. We studied an idealised OAE application in a natural low-nutrient ecosystem over 1 month. Our results showed that biogeochemical functioning remained mostly stable but that the long-term capability for storing carbon may be limited at high alkalinity concentration.
Alain Fumenia, Hubert Loisel, Rick A. Reynolds, and Dariusz Stramski
Biogeosciences, 22, 2461–2484, https://doi.org/10.5194/bg-22-2461-2025, https://doi.org/10.5194/bg-22-2461-2025, 2025
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Particulate organic nitrogen (PON) plays a central role in ocean biogeochemistry, yet limited in situ data hinder a full understanding of PON variability and associated processes. Measurements of optical properties offer an alternative for assessing PON across diverse marine environments. Our analysis reveals strong relationships between PON and optical properties, supporting a promising means to assess PON from optical measurements performed in situ or conducted from remote-sensing platforms.
Madhavan Girijakumari Keerthi, Olivier Aumont, Lester Kwiatkowski, and Marina Levy
Biogeosciences, 22, 2163–2180, https://doi.org/10.5194/bg-22-2163-2025, https://doi.org/10.5194/bg-22-2163-2025, 2025
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We assessed how well climate models replicate sub-seasonal changes in ocean chlorophyll observed by satellites. Models struggle to capture these variations accurately. Some overestimate fluctuations and their impact on annual chlorophyll variability, while others underestimate them. The underestimation is likely due to limited model resolution, while the overestimation may come from internal model oscillations.
Gesa Schulz, Kirstin Dähnke, Tina Sanders, Jan Penopp, Hermann W. Bange, Rena Czeschel, and Birgit Gaye
EGUsphere, https://doi.org/10.5194/egusphere-2025-1660, https://doi.org/10.5194/egusphere-2025-1660, 2025
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Oxygen minimum zones (OMZs) are low-oxygen ocean areas that deplete nitrogen, a key marine nutrient. Understanding nitrogen cycling in OMZs is crucial for the global nitrogen cycle. This study examined nitrogen cycling in the OMZ of the Bay of Bengal and East Equatorial Indian Ocean, revealing limited mixing between both regions. Surface phytoplankton consumes nitrate, while deeper nitrification recycles nitrogen. In the BoB’s OMZ (100–300 m), nitrogen loss likely occurs via anammox.
Adam V. Subhas, Jennie E. Rheuban, Zhaohui Aleck Wang, Daniel C. McCorkle, Anna P. M. Michel, Lukas Marx, Chloe L. Dean, Kate Morkeski, Matthew G. Hayden, Mary Burkitt-Gray, Francis Elder, Yiming Guo, Heather H. Kim, and Ke Chen
EGUsphere, https://doi.org/10.5194/egusphere-2025-1348, https://doi.org/10.5194/egusphere-2025-1348, 2025
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Ocean alkalinity enhancement (OAE) is a carbon removal approach in which alkaline materials are added to the marine environment, increasing the ocean's ability to store carbon dioxide. We conducted an open-water experiment releasing and tracking a fluorescent water tracer. Under the right conditions, in-water monitoring of OAE does appear to be possible. We conclude with a series of practical recommendations for open-water OAE monitoring.
Jens Terhaar
Biogeosciences, 22, 1631–1649, https://doi.org/10.5194/bg-22-1631-2025, https://doi.org/10.5194/bg-22-1631-2025, 2025
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The ocean is a major natural carbon sink. Despite its importance, estimates of the ocean carbon sink remain uncertain. Here, I present a hybrid model estimate of the ocean carbon sink from 1959 to 2022. By combining ocean models in hindcast mode and Earth system models, I keep the strength of each approach and remove the respective weaknesses. This composite model estimate is similar in magnitude to the best estimate of the Global Carbon Budget but 70 % less uncertain.
Huailin Deng, Koji Suzuki, Ichiro Yasuda, Hiroshi Ogawa, and Jun Nishioka
Biogeosciences, 22, 1495–1508, https://doi.org/10.5194/bg-22-1495-2025, https://doi.org/10.5194/bg-22-1495-2025, 2025
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Iron (Fe) and nitrate are vital for primary production in the North Pacific. Sedimentary Fe is carried by North Pacific Intermediate Water to the North Pacific, but the nutrient return path and its effect on phytoplankton are unclear. By combining Fe and macronutrient fluxes with phytoplankton composition, this study firstly revealed that Fe supply from the subsurface greatly controls diatom abundance and identified the nutrient return path in the subarctic gyre and Kuroshio–Oyashio transition area.
Alexandre Accardo, Rémi Laxenaire, Alberto Baudena, Sabrina Speich, Rainer Kiko, and Lars Stemmann
Biogeosciences, 22, 1183–1201, https://doi.org/10.5194/bg-22-1183-2025, https://doi.org/10.5194/bg-22-1183-2025, 2025
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The open ocean helps mitigate climate change by storing CO2 via the biological carbon pump (BCP), which involves processes like organic carbon production at the surface and transferring it to the deep ocean via various pathways. By deploying an autonomous platform, we found significant marine snow accumulation from the surface to the mesopelagic zone in frontal regions between eddies. We suggest that the coupling of hydrodynamics at eddy edges and biological activity may enhance this process.
Naoya Kanna, Kazutaka Tateyama, Takuji Waseda, Anna Timofeeva, Maria Papadimitraki, Laura Whitmore, Hajime Obata, Daiki Nomura, Hiroshi Ogawa, Youhei Yamashita, and Igor Polyakov
Biogeosciences, 22, 1057–1076, https://doi.org/10.5194/bg-22-1057-2025, https://doi.org/10.5194/bg-22-1057-2025, 2025
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This article presents data on iron and manganese, essential micronutrients for primary producers in the Arctic Laptev and East Siberian seas (LESS). There, observations were made through international cooperation with the Nansen and Amundsen Basin Observational System expedition during the late summer of 2021. The results from this study indicate that the major sources controlling the iron and manganese distributions on the LESS continental margins are river discharge and shelf sediment input.
Ben J. Fisher, Alex J. Poulton, Michael P. Meredith, Kimberlee Baldry, Oscar Schofield, and Sian F. Henley
Biogeosciences, 22, 975–994, https://doi.org/10.5194/bg-22-975-2025, https://doi.org/10.5194/bg-22-975-2025, 2025
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The Southern Ocean is a rapidly warming environment, with subsequent impacts on ecosystems and biogeochemical cycling. This study examines changes in phytoplankton and biogeochemistry using a range of climate models. Under climate change, the Southern Ocean will be warmer, more acidic and more productive and will have reduced nutrient availability by 2100. However, there is substantial variability between models across key productivity parameters. We propose ways of reducing this uncertainty.
Pearse J. Buchanan, Juan J. Pierella Karlusich, Robyn E. Tuerena, Roxana Shafiee, E. Malcolm S. Woodward, Chris Bowler, and Alessandro Tagliabue
EGUsphere, https://doi.org/10.5194/egusphere-2024-3639, https://doi.org/10.5194/egusphere-2024-3639, 2025
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Ammonium is a form of nitrogen that may become more important for growth of marine primary producers (i.e., phytoplankton) in the future. Because some phytoplankton taxa have a greater affinity for ammonium than others, the relative increase in ammonium could cause shifts in community composition. We quantify ammonium enrichment, identify its drivers, and isolate the possible effect on phytoplankton community composition under a high emissions scenario.
David Curbelo-Hernández, Fiz F. Pérez, Melchor González-Dávila, Sergey V. Gladyshev, Aridane G. González, David González-Santana, Antón Velo, Alexey Sokov, and J. Magdalena Santana-Casiano
Biogeosciences, 21, 5561–5589, https://doi.org/10.5194/bg-21-5561-2024, https://doi.org/10.5194/bg-21-5561-2024, 2024
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The study evaluated CO2–carbonate system dynamics in the North Atlantic subpolar gyre during 2009–2019. Significant ocean acidification, largely due to rising anthropogenic CO2 levels, was found. Cooling, freshening, and enhanced convective processes intensified this trend, affecting calcite and aragonite saturation. The findings contribute to a deeper understanding of ocean acidification and improve our knowledge about its impact on marine ecosystems.
Yuye Han, Zvi Steiner, Zhimian Cao, Di Fan, Junhui Chen, Jimin Yu, and Minhan Dai
EGUsphere, https://doi.org/10.5194/egusphere-2024-3492, https://doi.org/10.5194/egusphere-2024-3492, 2024
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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.
Louise Delaigue, Gert-Jan Reichart, Chris Galley, Yasmina Ourradi, and Matthew Paul Humphreys
EGUsphere, https://doi.org/10.5194/egusphere-2024-2853, https://doi.org/10.5194/egusphere-2024-2853, 2024
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Our study analyzed pH in ocean surface waters to understand how they fluctuate with changes in temperature, salinity, and biological activities. We found that temperature mainly controls daily pH variations, but biological processes also play a role, especially in affecting CO2 levels between the ocean and atmosphere. Our research shows how these factors together maintain the balance of ocean chemistry, which is crucial for predicting changes in marine environments.
Medhavi Pandey, Haimanti Biswas, Daniel Birgel, Nicole Burdanowitz, and Birgit Gaye
Biogeosciences, 21, 4681–4698, https://doi.org/10.5194/bg-21-4681-2024, https://doi.org/10.5194/bg-21-4681-2024, 2024
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We analysed sea surface temperature (SST) proxy and plankton biomarkers in sediments that accumulate sinking material signatures from surface waters in the central Arabian Sea (21°–11° N, 64° E), a tropical basin impacted by monsoons. We saw a north–south SST gradient, and the biological proxies showed more organic matter from larger algae in the north. Smaller algae and zooplankton were more numerous in the south. These trends were related to ocean–atmospheric processes and oxygen availability.
Allison Hogikyan and Laure Resplandy
Biogeosciences, 21, 4621–4636, https://doi.org/10.5194/bg-21-4621-2024, https://doi.org/10.5194/bg-21-4621-2024, 2024
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Rising atmospheric CO2 influences ocean carbon chemistry, leading to ocean acidification. Global warming introduces spatial patterns in the intensity of ocean acidification. We show that the most prominent spatial patterns are controlled by warming-driven changes in rainfall and evaporation, not by the direct effect of warming on carbon chemistry and pH. These evaporation and rainfall patterns oppose acidification in saltier parts of the ocean and enhance acidification in fresher regions.
Shunya Koseki, Lander R. Crespo, Jerry Tjiputra, Filippa Fransner, Noel S. Keenlyside, and David Rivas
Biogeosciences, 21, 4149–4168, https://doi.org/10.5194/bg-21-4149-2024, https://doi.org/10.5194/bg-21-4149-2024, 2024
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We investigated how the physical biases of an Earth system model influence the marine biogeochemical processes in the tropical Atlantic. With four different configurations of the model, we have shown that the versions with better SST reproduction tend to better represent the primary production and air–sea CO2 flux in terms of climatology, seasonal cycle, and response to climate variability.
Lyuba Novi, Annalisa Bracco, Takamitsu Ito, and Yohei Takano
Biogeosciences, 21, 3985–4005, https://doi.org/10.5194/bg-21-3985-2024, https://doi.org/10.5194/bg-21-3985-2024, 2024
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We explored the relationship between oxygen and stratification in the North Pacific Ocean using a combination of data mining and machine learning. We used isopycnic potential vorticity (IPV) as an indicator to quantify ocean ventilation and analyzed its predictability, a strong O2–IPV connection, and predictability for IPV in the tropical Pacific. This opens new routes for monitoring ocean O2 through few observational sites co-located with more abundant IPV measurements in the tropical Pacific.
Winfred Marshal, Jing Xiang Chung, Nur Hidayah Roseli, Roswati Md Amin, and Mohd Fadzil Bin Mohd Akhir
Biogeosciences, 21, 4007–4035, https://doi.org/10.5194/bg-21-4007-2024, https://doi.org/10.5194/bg-21-4007-2024, 2024
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This study stands out for thoroughly examining CMIP6 ESMs' ability to simulate biogeochemical variables in the southern South China Sea, an economically important region. It assesses variables like chlorophyll, phytoplankton, nitrate, and oxygen on annual and seasonal scales. While global assessments exist, this study addresses a gap by objectively ranking 13 CMIP6 ocean biogeochemistry models' performance at a regional level, focusing on replicating specific observed biogeochemical variables.
Jens Terhaar
Biogeosciences, 21, 3903–3926, https://doi.org/10.5194/bg-21-3903-2024, https://doi.org/10.5194/bg-21-3903-2024, 2024
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Despite the ocean’s importance in the carbon cycle and hence the climate, observing the ocean carbon sink remains challenging. Here, I use an ensemble of 12 models to understand drivers of decadal trends of the past, present, and future ocean carbon sink. I show that 80 % of the decadal trends in the multi-model mean ocean carbon sink can be explained by changes in decadal trends in atmospheric CO2. The remaining 20 % are due to internal climate variability and ocean heat uptake.
Reiner Steinfeldt, Monika Rhein, and Dagmar Kieke
Biogeosciences, 21, 3839–3867, https://doi.org/10.5194/bg-21-3839-2024, https://doi.org/10.5194/bg-21-3839-2024, 2024
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We calculate the amount of anthropogenic carbon (Cant) in the Atlantic for the years 1990, 2000, 2010 and 2020. Cant is the carbon that is taken up by the ocean as a result of humanmade CO2 emissions. To determine the amount of Cant, we apply a technique that is based on the observations of other humanmade gases (e.g., chlorofluorocarbons). Regionally, changes in ocean ventilation have an impact on the storage of Cant. Overall, the increase in Cant is driven by the rising CO2 in the atmosphere.
Stephanie Delacroix, Tor Jensen Nystuen, August E. Dessen Tobiesen, Andrew L. King, and Erik Höglund
Biogeosciences, 21, 3677–3690, https://doi.org/10.5194/bg-21-3677-2024, https://doi.org/10.5194/bg-21-3677-2024, 2024
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The addition of alkaline minerals into the ocean might reduce excessive anthropogenic CO2 emissions. Magnesium hydroxide can be added in large amounts because of its low seawater solubility without reaching harmful pH levels. The toxicity effect results of magnesium hydroxide, by simulating the expected concentrations from a ship's dispersion scenario, demonstrated low impacts on both sensitive and local assemblages of marine microalgae when compared to calcium hydroxide.
Precious Mongwe, Matthew Long, Takamitsu Ito, Curtis Deutsch, and Yeray Santana-Falcón
Biogeosciences, 21, 3477–3490, https://doi.org/10.5194/bg-21-3477-2024, https://doi.org/10.5194/bg-21-3477-2024, 2024
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We use a collection of measurements that capture the physiological sensitivity of organisms to temperature and oxygen and a CESM1 large ensemble to investigate how natural climate variations and climate warming will impact the ability of marine heterotrophic marine organisms to support habitats in the future. We find that warming and dissolved oxygen loss over the next several decades will reduce the volume of ocean habitats and will increase organisms' vulnerability to extremes.
Charly A. Moras, Tyler Cyronak, Lennart T. Bach, Renaud Joannes-Boyau, and Kai G. Schulz
Biogeosciences, 21, 3463–3475, https://doi.org/10.5194/bg-21-3463-2024, https://doi.org/10.5194/bg-21-3463-2024, 2024
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We investigate the effects of mineral grain size and seawater salinity on magnesium hydroxide dissolution and calcium carbonate precipitation kinetics for ocean alkalinity enhancement. Salinity did not affect the dissolution, but calcium carbonate formed earlier at lower salinities due to the lower magnesium and dissolved organic carbon concentrations. Smaller grain sizes dissolved faster but calcium carbonate precipitated earlier, suggesting that medium grain sizes are optimal for kinetics.
Rosie M. Sheward, Christina Gebühr, Jörg Bollmann, and Jens O. Herrle
Biogeosciences, 21, 3121–3141, https://doi.org/10.5194/bg-21-3121-2024, https://doi.org/10.5194/bg-21-3121-2024, 2024
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How quickly do marine microorganisms respond to salinity stress? Our experiments with the calcifying marine plankton Emiliania huxleyi show that growth and cell morphology responded to salinity stress within as little as 24–48 hours, demonstrating that morphology and calcification are sensitive to salinity over a range of timescales. Our results have implications for understanding the short-term role of E. huxleyi in biogeochemical cycles and in size-based paleoproxies for salinity.
Laura Marín-Samper, Javier Arístegui, Nauzet Hernández-Hernández, Joaquín Ortiz, Stephen D. Archer, Andrea Ludwig, and Ulf Riebesell
Biogeosciences, 21, 2859–2876, https://doi.org/10.5194/bg-21-2859-2024, https://doi.org/10.5194/bg-21-2859-2024, 2024
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Our planet is facing a climate crisis. Scientists are working on innovative solutions that will aid in capturing the hard to abate emissions before it is too late. Exciting research reveals that ocean alkalinity enhancement, a key climate change mitigation strategy, does not harm phytoplankton, the cornerstone of marine ecosystems. Through meticulous study, we may have uncovered a positive relationship: up to a specific limit, enhancing ocean alkalinity boosts photosynthesis by certain species.
France Van Wambeke, Pascal Conan, Mireille Pujo-Pay, Vincent Taillandier, Olivier Crispi, Alexandra Pavlidou, Sandra Nunige, Morgane Didry, Christophe Salmeron, and Elvira Pulido-Villena
Biogeosciences, 21, 2621–2640, https://doi.org/10.5194/bg-21-2621-2024, https://doi.org/10.5194/bg-21-2621-2024, 2024
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Phosphomonoesterase (PME) and phosphodiesterase (PDE) activities over the epipelagic zone are described in the eastern Mediterranean Sea in winter and autumn. The types of concentration kinetics obtained for PDE (saturation at 50 µM, high Km, high turnover times) compared to those of PME (saturation at 1 µM, low Km, low turnover times) are discussed in regard to the possible inequal distribution of PDE and PME in the size continuum of organic material and accessibility to phosphodiesters.
Jenny Hieronymus, Magnus Hieronymus, Matthias Gröger, Jörg Schwinger, Raffaele Bernadello, Etienne Tourigny, Valentina Sicardi, Itzel Ruvalcaba Baroni, and Klaus Wyser
Biogeosciences, 21, 2189–2206, https://doi.org/10.5194/bg-21-2189-2024, https://doi.org/10.5194/bg-21-2189-2024, 2024
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The timing of the net primary production annual maxima in the North Atlantic in the period 1750–2100 is investigated using two Earth system models and the high-emissions scenario SSP5-8.5. It is found that, for most of the region, the annual maxima occur progressively earlier, with the most change occurring after the year 2000. Shifts in the seasonality of the primary production may impact the entire ecosystem, which highlights the need for long-term monitoring campaigns in this area.
Nicole M. Travis, Colette L. Kelly, and Karen L. Casciotti
Biogeosciences, 21, 1985–2004, https://doi.org/10.5194/bg-21-1985-2024, https://doi.org/10.5194/bg-21-1985-2024, 2024
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We conducted experimental manipulations of light level on microbial communities from the primary nitrite maximum. Overall, while individual microbial processes have different directions and magnitudes in their response to increasing light, the net community response is a decline in nitrite production with increasing light. We conclude that while increased light may decrease net nitrite production, high-light conditions alone do not exclude nitrification from occurring in the surface ocean.
Zoë Rebecca van Kemenade, Zeynep Erdem, Ellen Christine Hopmans, Jaap Smede Sinninghe Damsté, and Darci Rush
Biogeosciences, 21, 1517–1532, https://doi.org/10.5194/bg-21-1517-2024, https://doi.org/10.5194/bg-21-1517-2024, 2024
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The California Current system (CCS) hosts the eastern subtropical North Pacific oxygen minimum zone (ESTNP OMZ). This study shows anaerobic ammonium oxidizing (anammox) bacteria cause a loss of bioavailable nitrogen (N) in the ESTNP OMZ throughout the late Quaternary. Anammox occurred during both glacial and interglacial periods and was driven by the supply of organic matter and changes in ocean currents. These findings may have important consequences for biogeochemical models of the CCS.
Cathy Wimart-Rousseau, Tobias Steinhoff, Birgit Klein, Henry Bittig, and Arne Körtzinger
Biogeosciences, 21, 1191–1211, https://doi.org/10.5194/bg-21-1191-2024, https://doi.org/10.5194/bg-21-1191-2024, 2024
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The marine CO2 system can be measured independently and continuously by BGC-Argo floats since numerous pH sensors have been developed to suit these autonomous measurements platforms. By applying the Argo correction routines to float pH data acquired in the subpolar North Atlantic Ocean, we report the uncertainty and lack of objective criteria associated with the choice of the reference method as well the reference depth for the pH correction.
Sabine Mecking and Kyla Drushka
Biogeosciences, 21, 1117–1133, https://doi.org/10.5194/bg-21-1117-2024, https://doi.org/10.5194/bg-21-1117-2024, 2024
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This study investigates whether northeastern North Pacific oxygen changes may be caused by surface density changes in the northwest as water moves along density horizons from the surface into the subsurface ocean. A correlation is found with a lag that about matches the travel time of water from the northwest to the northeast. Salinity is the main driver causing decadal changes in surface density, whereas salinity and temperature contribute about equally to long-term declining density trends.
Takamitsu Ito, Hernan E. Garcia, Zhankun Wang, Shoshiro Minobe, Matthew C. Long, Just Cebrian, James Reagan, Tim Boyer, Christopher Paver, Courtney Bouchard, Yohei Takano, Seth Bushinsky, Ahron Cervania, and Curtis A. Deutsch
Biogeosciences, 21, 747–759, https://doi.org/10.5194/bg-21-747-2024, https://doi.org/10.5194/bg-21-747-2024, 2024
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This study aims to estimate how much oceanic oxygen has been lost and its uncertainties. One major source of uncertainty comes from the statistical gap-filling methods. Outputs from Earth system models are used to generate synthetic observations where oxygen data are extracted from the model output at the location and time of historical oceanographic cruises. Reconstructed oxygen trend is approximately two-thirds of the true trend.
Robert W. Izett, Katja Fennel, Adam C. Stoer, and David P. Nicholson
Biogeosciences, 21, 13–47, https://doi.org/10.5194/bg-21-13-2024, https://doi.org/10.5194/bg-21-13-2024, 2024
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This paper provides an overview of the capacity to expand the global coverage of marine primary production estimates using autonomous ocean-going instruments, called Biogeochemical-Argo floats. We review existing approaches to quantifying primary production using floats, provide examples of the current implementation of the methods, and offer insights into how they can be better exploited. This paper is timely, given the ongoing expansion of the Biogeochemical-Argo array.
Qian Liu, Yingjie Liu, and Xiaofeng Li
Biogeosciences, 20, 4857–4874, https://doi.org/10.5194/bg-20-4857-2023, https://doi.org/10.5194/bg-20-4857-2023, 2023
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In the Southern Ocean, abundant eddies behave opposite to our expectations. That is, anticyclonic (cyclonic) eddies are cold (warm). By investigating the variations of physical and biochemical parameters in eddies, we find that abnormal eddies have unique and significant effects on modulating the parameters. This study fills a gap in understanding the effects of abnormal eddies on physical and biochemical parameters in the Southern Ocean.
Caroline Ulses, Claude Estournel, Patrick Marsaleix, Karline Soetaert, Marine Fourrier, Laurent Coppola, Dominique Lefèvre, Franck Touratier, Catherine Goyet, Véronique Guglielmi, Fayçal Kessouri, Pierre Testor, and Xavier Durrieu de Madron
Biogeosciences, 20, 4683–4710, https://doi.org/10.5194/bg-20-4683-2023, https://doi.org/10.5194/bg-20-4683-2023, 2023
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Deep convection plays a key role in the circulation, thermodynamics, and biogeochemical cycles in the Mediterranean Sea, considered to be a hotspot of biodiversity and climate change. In this study, we investigate the seasonal and annual budget of dissolved inorganic carbon in the deep-convection area of the northwestern Mediterranean Sea.
Daniela König and Alessandro Tagliabue
Biogeosciences, 20, 4197–4212, https://doi.org/10.5194/bg-20-4197-2023, https://doi.org/10.5194/bg-20-4197-2023, 2023
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Using model simulations, we show that natural and anthropogenic changes in the global climate leave a distinct fingerprint in the isotopic signatures of iron in the surface ocean. We find that these climate effects on iron isotopes are often caused by the redistribution of iron from different external sources to the ocean, due to changes in ocean currents, and by changes in algal growth, which take up iron. Thus, isotopes may help detect climate-induced changes in iron supply and algal uptake.
Chloé Baumas, Robin Fuchs, Marc Garel, Jean-Christophe Poggiale, Laurent Memery, Frédéric A. C. Le Moigne, and Christian Tamburini
Biogeosciences, 20, 4165–4182, https://doi.org/10.5194/bg-20-4165-2023, https://doi.org/10.5194/bg-20-4165-2023, 2023
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Through the sink of particles in the ocean, carbon (C) is exported and sequestered when reaching 1000 m. Attempts to quantify C exported vs. C consumed by heterotrophs have increased. Yet most of the conducted estimations have led to C demands several times higher than C export. The choice of parameters greatly impacts the results. As theses parameters are overlooked, non-accurate values are often used. In this study we show that C budgets can be well balanced when using appropriate values.
Anna Belcher, Sian F. Henley, Katharine Hendry, Marianne Wootton, Lisa Friberg, Ursula Dallman, Tong Wang, Christopher Coath, and Clara Manno
Biogeosciences, 20, 3573–3591, https://doi.org/10.5194/bg-20-3573-2023, https://doi.org/10.5194/bg-20-3573-2023, 2023
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The oceans play a crucial role in the uptake of atmospheric carbon dioxide, particularly the Southern Ocean. The biological pumping of carbon from the surface to the deep ocean is key to this. Using sediment trap samples from the Scotia Sea, we examine biogeochemical fluxes of carbon, nitrogen, and biogenic silica and their stable isotope compositions. We find phytoplankton community structure and physically mediated processes are important controls on particulate fluxes to the deep ocean.
Asmita Singh, Susanne Fietz, Sandy J. Thomalla, Nicolas Sanchez, Murat V. Ardelan, Sébastien Moreau, Hanna M. Kauko, Agneta Fransson, Melissa Chierici, Saumik Samanta, Thato N. Mtshali, Alakendra N. Roychoudhury, and Thomas J. Ryan-Keogh
Biogeosciences, 20, 3073–3091, https://doi.org/10.5194/bg-20-3073-2023, https://doi.org/10.5194/bg-20-3073-2023, 2023
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Despite the scarcity of iron in the Southern Ocean, seasonal blooms occur due to changes in nutrient and light availability. Surprisingly, during an autumn bloom in the Antarctic sea-ice zone, the results from incubation experiments showed no significant photophysiological response of phytoplankton to iron addition. This suggests that ambient iron concentrations were sufficient, challenging the notion of iron deficiency in the Southern Ocean through extended iron-replete post-bloom conditions.
Benoît Pasquier, Mark Holzer, Matthew A. Chamberlain, Richard J. Matear, Nathaniel L. Bindoff, and François W. Primeau
Biogeosciences, 20, 2985–3009, https://doi.org/10.5194/bg-20-2985-2023, https://doi.org/10.5194/bg-20-2985-2023, 2023
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Modeling the ocean's carbon and oxygen cycles accurately is challenging. Parameter optimization improves the fit to observed tracers but can introduce artifacts in the biological pump. Organic-matter production and subsurface remineralization rates adjust to compensate for circulation biases, changing the pathways and timescales with which nutrients return to the surface. Circulation biases can thus strongly alter the system’s response to ecological change, even when parameters are optimized.
Priyanka Banerjee
Biogeosciences, 20, 2613–2643, https://doi.org/10.5194/bg-20-2613-2023, https://doi.org/10.5194/bg-20-2613-2023, 2023
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This study shows that atmospheric deposition is the most important source of iron to the upper northern Indian Ocean for phytoplankton growth. This is followed by iron from continental-shelf sediment. Phytoplankton increase following iron addition is possible only with high background levels of nitrate. Vertical mixing is the most important physical process supplying iron to the upper ocean in this region throughout the year. The importance of ocean currents in supplying iron varies seasonally.
Iris Kriest, Julia Getzlaff, Angela Landolfi, Volkmar Sauerland, Markus Schartau, and Andreas Oschlies
Biogeosciences, 20, 2645–2669, https://doi.org/10.5194/bg-20-2645-2023, https://doi.org/10.5194/bg-20-2645-2023, 2023
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Global biogeochemical ocean models are often subjectively assessed and tuned against observations. We applied different strategies to calibrate a global model against observations. Although the calibrated models show similar tracer distributions at the surface, they differ in global biogeochemical fluxes, especially in global particle flux. Simulated global volume of oxygen minimum zones varies strongly with calibration strategy and over time, rendering its temporal extrapolation difficult.
John C. Tracey, Andrew R. Babbin, Elizabeth Wallace, Xin Sun, Katherine L. DuRussel, Claudia Frey, Donald E. Martocello III, Tyler Tamasi, Sergey Oleynik, and Bess B. Ward
Biogeosciences, 20, 2499–2523, https://doi.org/10.5194/bg-20-2499-2023, https://doi.org/10.5194/bg-20-2499-2023, 2023
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Nitrogen (N) is essential for life; thus, its availability plays a key role in determining marine productivity. Using incubations of seawater spiked with a rare form of N measurable on a mass spectrometer, we quantified microbial pathways that determine marine N availability. The results show that pathways that recycle N have higher rates than those that result in its loss from biomass and present new evidence for anaerobic nitrite oxidation, a process long thought to be strictly aerobic.
Amanda Gerotto, Hongrui Zhang, Renata Hanae Nagai, Heather M. Stoll, Rubens César Lopes Figueira, Chuanlian Liu, and Iván Hernández-Almeida
Biogeosciences, 20, 1725–1739, https://doi.org/10.5194/bg-20-1725-2023, https://doi.org/10.5194/bg-20-1725-2023, 2023
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Based on the analysis of the response of coccolithophores’ morphological attributes in a laboratory dissolution experiment and surface sediment samples from the South China Sea, we proposed that the thickness shape (ks) factor of fossil coccoliths together with the normalized ks variation, which is the ratio of the standard deviation of ks (σ) over the mean ks (σ/ks), is a robust and novel proxy to reconstruct past changes in deep ocean carbon chemistry.
Katherine E. Turner, Doug M. Smith, Anna Katavouta, and Richard G. Williams
Biogeosciences, 20, 1671–1690, https://doi.org/10.5194/bg-20-1671-2023, https://doi.org/10.5194/bg-20-1671-2023, 2023
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We present a new method for reconstructing ocean carbon using climate models and temperature and salinity observations. To test this method, we reconstruct modelled carbon using synthetic observations consistent with current sampling programmes. Sensitivity tests show skill in reconstructing carbon trends and variability within the upper 2000 m. Our results indicate that this method can be used for a new global estimate for ocean carbon content.
Alexandre Mignot, Hervé Claustre, Gianpiero Cossarini, Fabrizio D'Ortenzio, Elodie Gutknecht, Julien Lamouroux, Paolo Lazzari, Coralie Perruche, Stefano Salon, Raphaëlle Sauzède, Vincent Taillandier, and Anna Teruzzi
Biogeosciences, 20, 1405–1422, https://doi.org/10.5194/bg-20-1405-2023, https://doi.org/10.5194/bg-20-1405-2023, 2023
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Numerical models of ocean biogeochemistry are becoming a major tool to detect and predict the impact of climate change on marine resources and monitor ocean health. Here, we demonstrate the use of the global array of BGC-Argo floats for the assessment of biogeochemical models. We first detail the handling of the BGC-Argo data set for model assessment purposes. We then present 23 assessment metrics to quantify the consistency of BGC model simulations with respect to BGC-Argo data.
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