Articles | Volume 12, issue 5
Biogeosciences, 12, 1415–1430, 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: KEOPS2: Kerguelen Ocean and Plateau Study 2
| Highlight paper
05 Mar 2015
Research article | Highlight paper | 05 Mar 2015
Use of Ra isotopes to deduce rapid transfer of sediment-derived inputs off Kerguelen
V. Sanial et al.
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
Revised manuscript has not been submitted
Stanley Ifeanyi Nmor, Eric Viollier, Lucie Pastor, Bruno Lansard, Christophe Rabouille, and Karline Soetaert
Geosci. Model Dev. Discuss.,
Revised manuscript under review for GMDShort summary
The coastal marine environment serves as a transition zone in the land-ocean continuum and is susceptible to episodic phenomena such as flash floods, which cause massive organic matter deposition. Here, we present a model of sediment early diagenesis that explicitly describes this type of deposition while also incorporating unique flood deposit characteristics. This model can be used to investigate the temporal evolution of marine sediments following abrupt changes in environmental conditions.
Philippe Massicotte, Rainer M. W. Amon, David Antoine, Philippe Archambault, Sergio Balzano, Simon Bélanger, Ronald Benner, Dominique Boeuf, Annick Bricaud, Flavienne Bruyant, Gwenaëlle Chaillou, Malik Chami, Bruno Charrière, Jing Chen, Hervé Claustre, Pierre Coupel, Nicole Delsaut, David Doxaran, Jens Ehn, Cédric Fichot, Marie-Hélène Forget, Pingqing Fu, Jonathan Gagnon, Nicole Garcia, Beat Gasser, Jean-François Ghiglione, Gaby Gorsky, Michel Gosselin, Priscillia Gourvil, Yves Gratton, Pascal Guillot, Hermann J. Heipieper, Serge Heussner, Stanford B. Hooker, Yannick Huot, Christian Jeanthon, Wade Jeffrey, Fabien Joux, Kimitaka Kawamura, Bruno Lansard, Edouard Leymarie, Heike Link, Connie Lovejoy, Claudie Marec, Dominique Marie, Johannie Martin, Jacobo Martín, Guillaume Massé, Atsushi Matsuoka, Vanessa McKague, Alexandre Mignot, William L. Miller, Juan-Carlos Miquel, Alfonso Mucci, Kaori Ono, Eva Ortega-Retuerta, Christos Panagiotopoulos, Tim Papakyriakou, Marc Picheral, Louis Prieur, Patrick Raimbault, Joséphine Ras, Rick A. Reynolds, André Rochon, Jean-François Rontani, Catherine Schmechtig, Sabine Schmidt, Richard Sempéré, Yuan Shen, Guisheng Song, Dariusz Stramski, Eri Tachibana, Alexandre Thirouard, Imma Tolosa, Jean-Éric Tremblay, Mickael Vaïtilingom, Daniel Vaulot, Frédéric Vaultier, John K. Volkman, Huixiang Xie, Guangming Zheng, and Marcel Babin
Earth Syst. Sci. Data, 13, 1561–1592,Short summary
The MALINA oceanographic expedition was conducted in the Mackenzie River and the Beaufort Sea systems. The sampling was performed across seven shelf–basin transects to capture the meridional gradient between the estuary and the open ocean. The main goal of this research program was to better understand how processes such as primary production are influencing the fate of organic matter originating from the surrounding terrestrial landscape during its transition toward the Arctic Ocean.
Eleonora Fossile, Maria Pia Nardelli, Arbia Jouini, Bruno Lansard, Antonio Pusceddu, Davide Moccia, Elisabeth Michel, Olivier Péron, Hélène Howa, and Meryem Mojtahid
Biogeosciences, 17, 1933–1953,Short summary
This study focuses on benthic foraminiferal distribution in an Arctic fjord characterised by continuous sea ice production during winter and the consequent cascading of salty and corrosive waters (brine) to the seabed. The inner fjord is dominated by calcareous species (C). In the central deep basins, where brines are persistent, calcareous foraminifera are dissolved and agglutinated (A) dominate. The high A/C ratio is suggested as a proxy for brine persistence and sea ice production.
Jens Rassmann, Eryn M. Eitel, Bruno Lansard, Cécile Cathalot, Christophe Brandily, Martial Taillefert, and Christophe Rabouille
Biogeosciences, 17, 13–33,Short summary
In this paper, we use a large set of measurements made using in situ and lab techniques to elucidate the cause of dissolved inorganic carbon fluxes in sediments from the Rhône delta and its companion compound alkalinity, which carries the absorption capacity of coastal waters with respect to atmospheric CO2. We show that sediment processes (sulfate reduction, FeS precipitation and accumulation) are crucial in generating the alkalinity fluxes observed in this study by in situ incubation chambers.
Jens K. Ehn, Rick A. Reynolds, Dariusz Stramski, David Doxaran, Bruno Lansard, and Marcel Babin
Biogeosciences, 16, 1583–1605,Short summary
Beam attenuation at 660 nm and suspended particle matter (SPM) relationships were determined during the MALINA cruise in August 2009 to the Canadian Beaufort Sea in order to expand our knowledge of particle distributions in Arctic shelf seas. The relationship was then used to determine SPM distributions for four other expeditions to the region. SPM patterns on the shelf were explained by an interplay between wind forcing, river discharge, and melting sea ice that controls the circulation.
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
Biogeosciences, 15, 7097–7109,Short summary
The GEOVIDE cruise (GEOTRACES Section GA01) was conducted in the North Atlantic Ocean and Labrador Sea in May–June 2014. In this special issue, results from GEOVIDE, including physical oceanography and trace element and isotope cyclings, are presented among 17 articles. Here, the scientific context, project objectives, and scientific strategy of GEOVIDE are provided, along with an overview of the main results from the articles published in the special issue.
Mathieu Rembauville, Stéphane Blain, Clara Manno, Geraint Tarling, Anu Thompson, George Wolff, and Ian Salter
Biogeosciences, 15, 3071–3084,Short summary
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.
Emilie Le Roy, Virginie Sanial, Matthew A. Charette, Pieter van Beek, François Lacan, Stéphanie H. M. Jacquet, Paul B. Henderson, Marc Souhaut, Maribel I. García-Ibáñez, Catherine Jeandel, Fiz F. Pérez, and Géraldine Sarthou
Biogeosciences, 15, 3027–3048,Short summary
We report detailed sections of radium-226 (226Ra, T1/2 = 1602 y) activities and barium (Ba) concentrations determined in the North Atlantic (Portugal–Greenland–Canada) in the framework of the international GEOTRACES program (GA01 section–GEOVIDE project, May–July 2014). Dissolved 226Ra and Ba are strongly correlated along the section, which may reflect their similar chemical behavior.
Ivia Closset, Damien Cardinal, Mathieu Rembauville, François Thil, and Stéphane Blain
Biogeosciences, 13, 6049–6066,Short summary
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.
Jens Rassmann, Bruno Lansard, Lara Pozzato, and Christophe Rabouille
Biogeosciences, 13, 5379–5394,Short summary
In situ O2 and pH measurements as well as determination of porewater concentrations of dissolved inorganic carbon, total alkalinity, sulfate and calcium have been measured in the sediments of the Rhône prodelta. Biogeochemical activity decreased with distance from the river mouth. Oxic processes decreased the carbonate saturation state (Ω) by lowering pH, whereas anaerobic organic matter degradation, dominated by sulfate reduction, was accompanied by increasing Ω and carbonate precipitation.
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,Short summary
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.
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,Short summary
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.
F. Carlotti, M.-P. Jouandet, A. Nowaczyk, M. Harmelin-Vivien, D. Lefèvre, P. Richard, Y. Zhu, and M. Zhou
Biogeosciences, 12, 4543–4563,
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,Short summary
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,Short summary
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.
M. Rembauville, I. Salter, N. Leblond, A. Gueneugues, and S. Blain
Biogeosciences, 12, 3153–3170,
M. Rembauville, S. Blain, L. Armand, B. Quéguiner, and I. Salter
Biogeosciences, 12, 3171–3195,
I. Obernosterer, M. Fourquez, and S. Blain
Biogeosciences, 12, 1983–1992,
M. Fourquez, I. Obernosterer, D. M. Davies, T. W. Trull, and S. Blain
Biogeosciences, 12, 1893–1906,Short summary
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.
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,Short summary
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.
E. C. Laurenceau-Cornec, T. W. Trull, D. M. Davies, S. G. Bray, J. Doran, F. Planchon, F. Carlotti, M.-P. Jouandet, A.-J. Cavagna, A. M. Waite, and S. Blain
Biogeosciences, 12, 1007–1027,
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,Short summary
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,
C. Lo Monaco, N. Metzl, F. D'Ovidio, J. Llort, and C. Ridame
Revised manuscript has not been submitted
U. Christaki, D. Lefèvre, C. Georges, J. Colombet, P. Catala, C. Courties, T. Sime-Ngando, S. Blain, and I. Obernosterer
Biogeosciences, 11, 6739–6753,Short summary
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,
M.-P. Jouandet, G. A. Jackson, F. Carlotti, M. Picheral, L. Stemmann, and S. Blain
Biogeosciences, 11, 4393–4406,
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
Revised manuscript has not been submitted
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,
Related subject area
Biogeochemistry: Open OceanEarly winter barium excess in the southern Indian Ocean as an annual remineralisation proxy (GEOTRACES GIPr07 cruise)Controlling factors on the global distribution of a representative marine non-cyanobacterial diazotroph phylotype (Gamma A)Summer trends and drivers of sea surface fCO2 and pH changes observed in the southern Indian Ocean over the last two decades (1998–2019)Global nutrient cycling by commercially targeted marine fishMajor processes of the dissolved cobalt cycle in the North and equatorial Pacific OceanThe impact of the South-East Madagascar Bloom on the oceanic CO2 sinkNitrite regeneration in the oligotrophic Atlantic OceanBridging the gaps between particulate backscattering measurements and modeled particulate organic carbon in the oceanBiological production in two contrasted regions of the Mediterranean Sea during the oligotrophic period: an estimate based on the diel cycle of optical properties measured by BioGeoChemical-Argo profiling floatsAcidification of the Nordic SeasReconstruction of global surface ocean pCO2 using region-specific predictors based on a stepwise FFNN regression algorithmBiogeochemical controls on ammonium accumulation in the surface layer of the Southern OceanOxygen export to the deep ocean following Labrador Sea Water formationN2 fixation in the Mediterranean Sea related to the composition of the diazotrophic community and impact of dust under present and future environmental conditionsDissolution of a submarine carbonate platform by a submerged lake of acidic seawaterSeasonal flux patterns and carbon transport from low-oxygen eddies at the Cape Verde Ocean Observatory: lessons learned from a time series sediment trap study (2009–2016)Subsurface iron accumulation and rapid aluminum removal in the Mediterranean following African dust depositionLong-distance particle transport to the central Ionian SeaDeep chlorophyll maximum and nutricline in the Mediterranean Sea: emerging properties from a multi-platform assimilated biogeochemical model experimentPhosphorus cycling in the upper waters of the Mediterranean Sea (PEACETIME cruise): relative contribution of external and internal sourcesFast local warming is the main driver of recent deoxygenation in the northern Arabian SeaInfluence of atmospheric deposition on biogeochemical cycles in an oligotrophic ocean systemImpact of dust addition on the metabolism of Mediterranean plankton communities and carbon export under present and future conditions of pH and temperatureComparing CLE-AdCSV applications using SA and TAC to determine the Fe-binding characteristics of model ligands in seawaterImpact of dust addition on Mediterranean plankton communities under present and future conditions of pH and temperature: an experimental overviewReviews and syntheses: Trends in primary production in the Bay of Bengal – is it at a tipping point?Incorporating the stable carbon isotope 13C in the ocean biogeochemical component of the Max Planck Institute Earth System ModelSeasonal cycling of zinc and cobalt in the south-eastern Atlantic along the GEOTRACES GA10 sectionCarbon export and fate beneath a dynamic upwelled filament off the California coastContrasted release of insoluble elements (Fe, Al, rare earth elements, Th, Pa) after dust deposition in seawater: a tank experiment approachOn the barium–oxygen consumption relationship in the Mediterranean Sea: implications for mesopelagic marine snow remineralizationCompound high-temperature and low-chlorophyll extremes in the ocean over the satellite periodCan machine learning extract the mechanisms controlling phytoplankton growth from large-scale observations? – A proof-of-concept studyReviews and syntheses: The biogeochemical cycle of silicon in the modern oceanOxygen budget of the north-western Mediterranean deep- convection regionCross-basin differences in the nutrient assimilation characteristics of induced phytoplankton blooms in the subtropical Pacific watersDynamics of the deep chlorophyll maximum in the Black Sea as depicted by BGC-Argo floatsNitrate assimilation and regeneration in the Barents Sea: insights from nitrate isotopesAssimilating synthetic Biogeochemical-Argo and ocean colour observations into a global ocean model to inform observing system designSouthern Ocean Biogeochemical Argo detect under-ice phytoplankton growth before sea ice retreatA new intermittent regime of convective ventilation threatens the Black Sea oxygenation statusReviews and syntheses: Present, past, and future of the oxygen minimum zone in the northern Indian OceanParticulate rare earth element behavior in the North Atlantic (GEOVIDE cruise)Elevated sources of cobalt in the Arctic OceanIncrease in ocean acidity variability and extremes under increasing atmospheric CO2Can ocean community production and respiration be determined by measuring high-frequency oxygen profiles from autonomous floats?Assessing the value of biogeochemical Argo profiles versus ocean color observations for biogeochemical model optimization in the Gulf of MexicoThe Southern Annular Mode (SAM) influences phytoplankton communities in the seasonal ice zone of the Southern OceanProfiling float observation of thermohaline staircases in the western Mediterranean Sea and impact on nutrient fluxesOcean carbonate system variability in the North Atlantic Subpolar surface water (1993–2017)
Natasha René van Horsten, Hélène Planquette, Géraldine Sarthou, Thomas James Ryan-Keogh, Nolwenn Lemaitre, Thato Nicholas Mtshali, Alakendra Roychoudhury, and Eva Bucciarelli
Biogeosciences, 19, 3209–3224,Short summary
The remineralisation proxy, barite, was measured along 30°E in the southern Indian Ocean during early austral winter. To our knowledge this is the first reported Southern Ocean winter study. Concentrations throughout the water column were comparable to observations during spring to autumn. By linking satellite primary production to this proxy a possible annual timescale is proposed. These findings also suggest possible carbon remineralisation from satellite data on a basin scale.
Zhibo Shao and Ya-Wei Luo
Biogeosciences, 19, 2939–2952,Short summary
Non-cyanobacterial diazotrophs (NCDs) may be an important player in fixing N2 in the ocean. By conducting meta-analyses, we found that a representative marine NCD phylotype, Gamma A, tends to inhabit ocean environments with high productivity, low iron concentration and high light intensity. It also appears to be more abundant inside cyclonic eddies. Our study suggests a niche differentiation of NCDs from cyanobacterial diazotrophs as the latter prefers low-productivity and high-iron oceans.
Coraline Leseurre, Claire Lo Monaco, Gilles Reverdin, Nicolas Metzl, Jonathan Fin, Claude Mignon, and Léa Benito
Biogeosciences, 19, 2599–2625,Short summary
Decadal trends of fugacity of CO2 (fCO2), total alkalinity (AT), total carbon (CT) and pH in surface waters are investigated in different domains of the southern Indian Ocean (45°S–57°S) from ongoing and station observations regularly conducted in summer over the period 1998–2019. The fCO2 increase and pH decrease are mainly driven by anthropogenic CO2 estimated just below the summer mixed layer, as well as by a warming south of the polar front or in the fertilized waters near Kerguelen Island.
Priscilla Le Mézo, Jérôme Guiet, Kim Scherrer, Daniele Bianchi, and Eric Galbraith
Biogeosciences, 19, 2537–2555,Short summary
This study quantifies the role of commercially targeted fish biomass in the cycling of three important nutrients (N, P, and Fe), relative to nutrients otherwise available in water and to nutrients required by primary producers, and the impact of fishing. We use a model of commercially targeted fish biomass constrained by fish catch and stock assessment data to assess the contributions of fish at the global scale, at the time of the global peak catch and prior to industrial fishing.
Rebecca Chmiel, Nathan Lanning, Allison Laubach, Jong-Mi Lee, Jessica Fitzsimmons, Mariko Hatta, William Jenkins, Phoebe Lam, Matthew McIlvin, Alessandro Tagliabue, and Mak Saito
Biogeosciences, 19, 2365–2395,Short summary
Dissolved cobalt is present in trace amounts in seawater and is a necessary nutrient for marine microbes. On a transect from the Alaskan coast to Tahiti, we measured seawater concentrations of dissolved cobalt. Here, we describe several interesting features of the Pacific cobalt cycle including cobalt sources along the Alaskan coast and Hawaiian vents, deep-ocean particle formation, cobalt activity in low-oxygen regions, and how our samples compare to a global biogeochemical model’s predictions.
Nicolas Metzl, Claire Lo Monaco, Coraline Leseurre, Céline Ridame, Jonathan Fin, Claude Mignon, Marion Gehlen, and Thi Tuyet Trang Chau
Biogeosciences, 19, 1451–1468,Short summary
During an oceanographic cruise conducted in January 2020 in the south-western Indian Ocean, we observed very low CO2 concentrations associated with a strong phytoplankton bloom that occurred south-east of Madagascar. This biological event led to a strong regional CO2 ocean sink not previously observed.
Darren R. Clark, Andrew P. Rees, Charissa M. Ferrera, Lisa Al-Moosawi, Paul J. Somerfield, Carolyn Harris, Graham D. Quartly, Stephen Goult, Glen Tarran, and Gennadi Lessin
Biogeosciences, 19, 1355–1376,Short summary
Measurements of microbial processes were made in the sunlit open ocean during a research cruise (AMT19) between the UK and Chile. These help us to understand how microbial communities maintain the function of remote ecosystems. We find that the nitrogen cycling microbes which produce nitrite respond to changes in the environment. Our insights will aid the development of models that aim to replicate and ultimately project how marine environments may respond to ongoing climate change.
Martí Galí, Marcus Falls, Hervé Claustre, Olivier Aumont, and Raffaele Bernardello
Biogeosciences, 19, 1245–1275,Short summary
Part of the organic matter produced by plankton in the upper ocean is exported to the deep ocean. This process, known as the biological carbon pump, is key for the regulation of atmospheric carbon dioxide and global climate. However, the dynamics of organic particles below the upper ocean layer are not well understood. Here we compared the measurements acquired by autonomous robots in the top 1000 m of the ocean to a numerical model, which can help improve future climate projections.
Marie Barbieux, Julia Uitz, Alexandre Mignot, Collin Roesler, Hervé Claustre, Bernard Gentili, Vincent Taillandier, Fabrizio D'Ortenzio, Hubert Loisel, Antoine Poteau, Edouard Leymarie, Christophe Penkerc'h, Catherine Schmechtig, and Annick Bricaud
Biogeosciences, 19, 1165–1194,Short summary
This study assesses marine biological production in two Mediterranean systems representative of vast desert-like (oligotrophic) areas encountered in the global ocean. We use a novel approach based on non-intrusive high-frequency in situ measurements by two profiling robots, the BioGeoChemical-Argo (BGC-Argo) floats. Our results indicate substantial yet variable production rates and contribution to the whole water column of the subsurface layer, typically considered steady and non-productive.
Filippa Fransner, Friederike Fröb, Jerry Tjiputra, Nadine Goris, Siv K. Lauvset, Ingunn Skjelvan, Emil Jeansson, Abdirahman Omar, Melissa Chierici, Elizabeth Jones, Agneta Fransson, Sólveig R. Ólafsdóttir, Truls Johannessen, and Are Olsen
Biogeosciences, 19, 979–1012,Short summary
Ocean acidification, a direct consequence of the CO2 release by human activities, is a serious threat to marine ecosystems. In this study, we conduct a detailed investigation of the acidification of the Nordic Seas, from 1850 to 2100, by using a large set of samples taken during research cruises together with numerical model simulations. We estimate the effects of changes in different environmental factors on the rate of acidification and its potential effects on cold-water corals.
Guorong Zhong, Xuegang Li, Jinming Song, Baoxiao Qu, Fan Wang, Yanjun Wang, Bin Zhang, Xiaoxia Sun, Wuchang Zhang, Zhenyan Wang, Jun Ma, Huamao Yuan, and Liqin Duan
Biogeosciences, 19, 845–859,Short summary
A predictor selection algorithm was constructed to decrease the predicting error in the surface ocean partial pressure of CO2 (pCO2) mapping by finding better combinations of pCO2 predictors in different regions. Compared with previous research using the same combination of predictors in all regions, using different predictors selected by the algorithm in different regions can effectively decrease pCO2 predicting errors.
Shantelle Smith, Katye E. Altieri, Mhlangabezi Mdutyana, David R. Walker, Ruan G. Parrott, Sedick Gallie, Kurt A. M. Spence, Jessica M. Burger, and Sarah E. Fawcett
Biogeosciences, 19, 715–741,Short summary
Ammonium is a crucial yet poorly understood component of the Southern Ocean nitrogen cycle. We attribute our finding of consistently high ammonium concentrations in the winter mixed layer to limited ammonium consumption and sustained ammonium production, conditions under which the Southern Ocean becomes a source of carbon dioxide to the atmosphere. From similar data collected over an annual cycle, we propose a seasonal cycle for ammonium in shallow polar waters – a first for the Southern Ocean.
Jannes Koelling, Dariia Atamanchuk, Johannes Karstensen, Patricia Handmann, and Douglas W. R. Wallace
Biogeosciences, 19, 437–454,Short summary
In this study, we investigate oxygen variability in the deep western boundary current in the Labrador Sea from multiyear moored records. We estimate that about half of the oxygen taken up in the interior Labrador Sea by air–sea gas exchange during deep water formation is exported southward the same year. Our results underline the complexity of the oxygen uptake and export in the Labrador Sea and highlight the important role this region plays in supplying oxygen to the deep ocean.
Céline Ridame, Julie Dinasquet, Søren Hallstrøm, Estelle Bigeard, Lasse Riemann, France Van Wambeke, Matthieu Bressac, Elvira Pulido-Villena, Vincent Taillandier, Fréderic Gazeau, Antonio Tovar-Sanchez, Anne-Claire Baudoux, and Cécile Guieu
Biogeosciences, 19, 415–435,Short summary
We show that in the Mediterranean Sea spatial variability in N2 fixation is related to the diazotrophic community composition reflecting different nutrient requirements among species. Nutrient supply by Saharan dust is of great importance to diazotrophs, as shown by the strong stimulation of N2 fixation after a simulated dust event under present and future climate conditions; the magnitude of stimulation depends on the degree of limitation related to the diazotrophic community composition.
Matthew P. Humphreys, Erik H. Meesters, Henk de Haas, Szabina Karancz, Louise Delaigue, Karel Bakker, Gerard Duineveld, Siham de Goeyse, Andreas F. Haas, Furu Mienis, Sharyn Ossebaar, and Fleur C. van Duyl
Biogeosciences, 19, 347–358,Short summary
A series of submarine sinkholes were recently discovered on Luymes Bank, part of Saba Bank, a carbonate platform in the Caribbean Netherlands. Here, we investigate the waters inside these sinkholes for the first time. One of the sinkholes contained a body of dense, low-oxygen and low-pH water, which we call the
acid lake. We use measurements of seawater chemistry to work out what processes were responsible for forming the acid lake and discuss the consequences for the carbonate platform.
Gerhard Fischer, Oscar E. Romero, Johannes Karstensen, Karl-Heinz Baumann, Nasrollah Moradi, Morten Iversen, Götz Ruhland, Marco Klann, and Arne Körtzinger
Biogeosciences, 18, 6479–6500,Short summary
Low-oxygen eddies in the eastern subtropical North Atlantic can form an oasis for phytoplankton growth. Here we report on particle flux dynamics at the oligotrophic Cape Verde Ocean Observatory. We observed consistent flux patterns during the passages of low-oxygen eddies. We found distinct flux peaks in late winter, clearly exceeding background fluxes. Our findings suggest that the low-oxygen eddies sequester higher organic carbon than expected for oligotrophic settings.
Matthieu Bressac, Thibaut Wagener, Nathalie Leblond, Antonio Tovar-Sánchez, Céline Ridame, Vincent Taillandier, Samuel Albani, Sophie Guasco, Aurélie Dufour, Stéphanie H. M. Jacquet, François Dulac, Karine Desboeufs, and Cécile Guieu
Biogeosciences, 18, 6435–6453,Short summary
Phytoplankton growth is limited by the availability of iron in about 50 % of the ocean. Atmospheric deposition of desert dust represents a key source of iron. Here, we present direct observations of dust deposition in the Mediterranean Sea. A key finding is that the input of iron from dust primarily occurred in the deep ocean, while previous studies mainly focused on the ocean surface. This new insight will enable us to better represent controls on global marine productivity in models.
Léo Berline, Andrea Michelangelo Doglioli, Anne Petrenko, Stéphanie Barrillon, Boris Espinasse, Frederic A. C. Le Moigne, François Simon-Bot, Melilotus Thyssen, and François Carlotti
Biogeosciences, 18, 6377–6392,Short summary
While the Ionian Sea is considered a nutrient-depleted and low-phytoplankton biomass area, it is a crossroad for water mass circulation. In the central Ionian Sea, we observed a strong contrast in particle distribution across a ~100 km long transect. Using remote sensing and Lagrangian simulations, we suggest that this contrast finds its origin in the long-distance transport of particles from the north, west and east of the Ionian Sea, where phytoplankton production was more intense.
Anna Teruzzi, Giorgio Bolzon, Laura Feudale, and Gianpiero Cossarini
Biogeosciences, 18, 6147–6166,Short summary
During summer, maxima of phytoplankton chlorophyll concentration (DCM) occur in the subsurface of the Mediterranean Sea and can play a relevant role in carbon sequestration into the ocean interior. A numerical model based on in situ and satellite observations provides insights into the range of DCM conditions across the relatively small Mediterranean Sea and shows a western DCM that is 25 % shallower and with a higher phytoplankton chlorophyll concentration than in the eastern Mediterranean.
Elvira Pulido-Villena, Karine Desboeufs, Kahina Djaoudi, France Van Wambeke, Stéphanie Barrillon, Andrea Doglioli, Anne Petrenko, Vincent Taillandier, Franck Fu, Tiphanie Gaillard, Sophie Guasco, Sandra Nunige, Sylvain Triquet, and Cécile Guieu
Biogeosciences, 18, 5871–5889,Short summary
We report on phosphorus dynamics in the surface layer of the Mediterranean Sea. Highly sensitive phosphate measurements revealed vertical gradients above the phosphacline. The relative contribution of diapycnal fluxes to total external supply of phosphate to the mixed layer decreased towards the east, where atmospheric deposition dominated. Taken together, external sources of phosphate contributed little to total supply, which was mainly sustained by enzymatic hydrolysis of organic phosphorus.
Zouhair Lachkar, Michael Mehari, Muchamad Al Azhar, Marina Lévy, and Shafer Smith
Biogeosciences, 18, 5831–5849,Short summary
This study documents and quantifies a significant recent oxygen decline in the upper layers of the Arabian Sea and explores its drivers. Using a modeling approach we show that the fast local warming of sea surface is the main factor causing this oxygen drop. Concomitant summer monsoon intensification contributes to this trend, although to a lesser extent. These changes exacerbate oxygen depletion in the subsurface, threatening marine habitats and altering the local biogeochemistry.
France Van Wambeke, Vincent Taillandier, Karine Desboeufs, Elvira Pulido-Villena, Julie Dinasquet, Anja Engel, Emilio Marañón, Céline Ridame, and Cécile Guieu
Biogeosciences, 18, 5699–5717,Short summary
Simultaneous in situ measurements of (dry and wet) atmospheric deposition and biogeochemical stocks and fluxes in the sunlit waters of the open Mediterranean Sea revealed complex physical and biological processes occurring within the mixed layer. Nitrogen (N) budgets were computed to compare the sources and sinks of N in the mixed layer. The transitory effect observed after a wet dust deposition impacted the microbial food web down to the deep chlorophyll maximum.
Frédéric Gazeau, France Van Wambeke, Emilio Marañón, Maria Pérez-Lorenzo, Samir Alliouane, Christian Stolpe, Thierry Blasco, Nathalie Leblond, Birthe Zäncker, Anja Engel, Barbara Marie, Julie Dinasquet, and Cécile Guieu
Biogeosciences, 18, 5423–5446,Short summary
Our study shows that the impact of dust deposition on primary production depends on the initial composition and metabolic state of the tested community and is constrained by the amount of nutrients added, to sustain both the fast response of heterotrophic prokaryotes and the delayed one of phytoplankton. Under future environmental conditions, heterotrophic metabolism will be more impacted than primary production, therefore reducing the capacity of surface waters to sequester anthropogenic CO2.
Loes J. A. Gerringa, Martha Gledhill, Indah Ardiningsih, Niels Muntjewerf, and Luis M. Laglera
Biogeosciences, 18, 5265–5289,Short summary
For 3 decades, competitive ligand exchange–adsorptive cathodic stripping voltammetry was used to estimate the Fe-binding capacity of organic matter in seawater. In this paper the performance of the competing ligands is compared through the analysis of a series of model ligands. The main finding of this paper is that the determined speciation parameters are not independent of the application, making interpretation of Fe speciation data more complex than it was thought before.
Frédéric Gazeau, Céline Ridame, France Van Wambeke, Samir Alliouane, Christian Stolpe, Jean-Olivier Irisson, Sophie Marro, Jean-Michel Grisoni, Guillaume De Liège, Sandra Nunige, Kahina Djaoudi, Elvira Pulido-Villena, Julie Dinasquet, Ingrid Obernosterer, Philippe Catala, and Cécile Guieu
Biogeosciences, 18, 5011–5034,Short summary
This paper shows that the impacts of Saharan dust deposition in different Mediterranean basins are as strong as those observed in coastal waters but differed substantially between the three tested stations, differences attributed to variable initial metabolic states. A stronger impact of warming and acidification on mineralization suggests a decreased capacity of Mediterranean surface communities to sequester CO2 following the deposition of atmospheric particles in the coming decades.
Carolin R. Löscher
Biogeosciences, 18, 4953–4963,Short summary
The Bay of Bengal (BoB) is classically seen as an ocean region with low primary production, which has been predicted to decrease even further. Here, the importance of such a trend is used to explore what could happen to the BoB's low-oxygen core waters if primary production decreases. Lower biological production leads to less oxygen loss in deeper waters by respiration; thus it could be that oxygen will not further decrease and the BoB will not become anoxic, different to other low-oxygen areas.
Bo Liu, Katharina D. Six, and Tatiana Ilyina
Biogeosciences, 18, 4389–4429,Short summary
We incorporate a new representation of the stable carbon isotope 13C in a global ocean biogeochemistry model. The model well reproduces the present-day 13C observations. We find a recent observation-based estimate of the oceanic 13C Suess effect (the decrease in 13C/12C ratio due to uptake of anthropogenic CO2; 13CSE) possibly underestimates 13CSE by 0.1–0.26 per mil. The new model will aid in better understanding the past ocean state via comparison to 13C/12C measurements from sediment cores.
Neil J. Wyatt, Angela Milne, Eric P. Achterberg, Thomas J. Browning, Heather A. Bouman, E. Malcolm S. Woodward, and Maeve C. Lohan
Biogeosciences, 18, 4265–4280,Short summary
Using data collected during two expeditions to the South Atlantic Ocean, we investigated how the interaction between external sources and biological activity influenced the availability of the trace metals zinc and cobalt. This is important as both metals play essential roles in the metabolism and growth of phytoplankton and thus influence primary productivity of the oceans. We found seasonal changes in both processes that helped explain upper-ocean trace metal cycling.
Hannah L. Bourne, James K. B. Bishop, Elizabeth J. Connors, and Todd J. Wood
Biogeosciences, 18, 3053–3086,Short summary
To learn how the biological carbon pump works in productive coastal upwelling systems, four autonomous carbon flux explorers measured carbon flux through the twilight zone beneath an offshore-flowing filament of biologically productive water. Strikingly different particle classes dominated the carbon fluxes during successive stages of the filament evolution over 30 d. Both flux and transfer efficiency were far greater than expected, suggesting an outsized filament impact in California waters.
Matthieu Roy-Barman, Lorna Foliot, Eric Douville, Nathalie Leblond, Fréderic Gazeau, Matthieu Bressac, Thibaut Wagener, Céline Ridame, Karine Desboeufs, and Cécile Guieu
Biogeosciences, 18, 2663–2678,Short summary
The release of insoluble elements such as aluminum (Al), iron (Fe), rare earth elements (REEs), thorium (Th) and protactinium (Pa) when Saharan dust falls over the Mediterranean Sea was studied during tank experiments under present and future climate conditions. Each element exhibited different dissolution kinetics and dissolution fractions (always lower than a few percent). Changes in temperature and/or pH under greenhouse conditions lead to a lower Th release and a higher light REE release.
Stéphanie H. M. Jacquet, Dominique Lefèvre, Christian Tamburini, Marc Garel, Frédéric A. C. Le Moigne, Nagib Bhairy, and Sophie Guasco
Biogeosciences, 18, 2205–2212,Short summary
We present new data concerning the relation between biogenic barium (Baxs, a tracer of carbon remineralization at mesopelagic depths), O2 consumption and prokaryotic heterotrophic production (PHP) in the Mediterranean Sea. The purpose of this paper is to improve our understanding of the relation between Baxs, PHP and O2 and to test the validity of the Dehairs transfer function in the Mediterranean Sea. This relation has never been tested in the Mediterranean Sea.
Natacha Le Grix, Jakob Zscheischler, Charlotte Laufkötter, Cecile S. Rousseaux, and Thomas L. Frölicher
Biogeosciences, 18, 2119–2137,Short summary
Marine ecosystems could suffer severe damage from the co-occurrence of a marine heat wave with extremely low chlorophyll concentration. Here, we provide a first assessment of compound marine heat wave and low-chlorophyll events in the global ocean from 1998 to 2018. We reveal hotspots of these compound events in the equatorial Pacific and in the Arabian Sea and show that they mostly occur in summer at high latitudes and their frequency is modulated by large-scale modes of climate variability.
Christopher Holder and Anand Gnanadesikan
Biogeosciences, 18, 1941–1970,Short summary
A challenge for marine ecologists in studying phytoplankton is linking small-scale relationships found in a lab to broader relationships observed on large scales in the environment. We investigated whether machine learning (ML) could help connect these small- and large-scale relationships. ML was able to provide qualitative information about the small-scale processes from large-scale information. This method could help identify important relationships from observations in future research.
Paul J. Tréguer, Jill N. Sutton, Mark Brzezinski, Matthew A. Charette, Timothy Devries, Stephanie Dutkiewicz, Claudia Ehlert, Jon Hawkings, Aude Leynaert, Su Mei Liu, Natalia Llopis Monferrer, María López-Acosta, Manuel Maldonado, Shaily Rahman, Lihua Ran, and Olivier Rouxel
Biogeosciences, 18, 1269–1289,Short summary
Silicon is the second most abundant element of the Earth's crust. In this review, we show that silicon inputs and outputs, to and from the world ocean, are 57 % and 37 % higher, respectively, than previous estimates. These changes are significant, modifying factors such as the geochemical residence time of silicon, which is now about 8000 years and 2 times faster than previously assumed. We also update the total biogenic silica pelagic production and provide an estimate for sponge production.
Caroline Ulses, Claude Estournel, Marine Fourrier, Laurent Coppola, Fayçal Kessouri, Dominique Lefèvre, and Patrick Marsaleix
Biogeosciences, 18, 937–960,Short summary
We analyse the seasonal cycle of O2 and estimate an annual O2 budget in the north-western Mediterranean deep-convection region, using a numerical model. We show that this region acts as a large sink of atmospheric O2 and as a major source of O2 for the western Mediterranean Sea. The decrease in the deep convection intensity predicted in recent projections may have important consequences on the overall uptake of O2 in the Mediterranean Sea and on the O2 exchanges with the Atlantic Ocean.
Fuminori Hashihama, Hiroaki Saito, Taketoshi Kodama, Saori Yasui-Tamura, Jota Kanda, Iwao Tanita, Hiroshi Ogawa, E. Malcolm S. Woodward, Philip W. Boyd, and Ken Furuya
Biogeosciences, 18, 897–915,Short summary
We investigated the nutrient assimilation characteristics of deep-water-induced phytoplankton blooms across the subtropical North and South Pacific Ocean. Nutrient drawdown ratios of dissolved inorganic nitrogen to phosphate were anomalously low in the western North Pacific, likely due to the high phosphate uptake capability of low-phosphate-adapted phytoplankton. The anomalous phosphate uptake might influence the maintenance of chronic phosphate depletion in the western North Pacific.
Florian Ricour, Arthur Capet, Fabrizio D'Ortenzio, Bruno Delille, and Marilaure Grégoire
Biogeosciences, 18, 755–774,Short summary
This paper addresses the phenology of the deep chlorophyll maximum (DCM) in the Black Sea (BS). We show that the DCM forms in March at a density level set by the winter mixed layer. It maintains this location until June, suggesting an influence of the DCM on light and nutrient profiles rather than mere adaptation to external factors. In summer, the DCM concentrates ~55 % of the chlorophyll in a 10 m layer at ~35 m depth and should be considered a major feature of the BS phytoplankton dynamics.
Robyn E. Tuerena, Joanne Hopkins, Raja S. Ganeshram, Louisa Norman, Camille de la Vega, Rachel Jeffreys, and Claire Mahaffey
Biogeosciences, 18, 637–653,Short summary
The Barents Sea is a rapidly changing shallow sea within the Arctic. Here, nitrate, an essential nutrient, is fully consumed by algae in surface waters during summer months. Nitrate is efficiently regenerated in the Barents Sea, and there is no evidence for nitrogen loss from the sediments by denitrification, which is prevalent on other Arctic shelves. This suggests that nitrogen availability in the Barents Sea is largely determined by the supply of nutrients in water masses from the Atlantic.
Biogeosciences, 18, 509–534,Short summary
Biogeochemical-Argo floats are starting to routinely measure ocean chlorophyll, nutrients, oxygen, and pH. This study generated synthetic observations representing two potential Biogeochemical-Argo observing system designs and created a data assimilation scheme to combine them with an ocean model. The proposed system of 1000 floats brought clear benefits to model results, with additional floats giving further benefit. Existing satellite ocean colour observations gave complementary information.
Mark Hague and Marcello Vichi
Biogeosciences, 18, 25–38,Short summary
This paper examines the question of what causes the rapid spring growth of microscopic marine algae (phytoplankton) in the ice-covered ocean surrounding Antarctica. One prominent hypothesis proposes that the melting of sea ice is the primary cause, while our results suggest that this is only part of the explanation. In particular, we show that phytoplankton are able to start growing before the sea ice melts appreciably, much earlier than previously thought.
Arthur Capet, Luc Vandenbulcke, and Marilaure Grégoire
Biogeosciences, 17, 6507–6525,Short summary
The Black Sea is 2000 m deep, but, due to limited ventilation, only about the upper 100 m contains enough oxygen to support marine life such as fish. This oxygenation depth has been shown to be decreasing (1955–2019). Here, we evidence that atmospheric warming induced a clear shift in an important ventilation mechanism. We highlight the impact of this shift on oxygenation. There are important implications for marine life and carbon and nutrient cycling if this new ventilation regime persists.
Tim Rixen, Greg Cowie, Birgit Gaye, Joaquim Goes, Helga do Rosário Gomes, Raleigh R. Hood, Zouhair Lachkar, Henrike Schmidt, Joachim Segschneider, and Arvind Singh
Biogeosciences, 17, 6051–6080,Short summary
The northern Indian Ocean hosts an extensive oxygen minimum zone (OMZ), which intensified due to human-induced global changes. This includes the occurrence of anoxic events on the Indian shelf and affects benthic ecosystems and the pelagic ecosystem structure in the Arabian Sea. Consequences for biogeochemical cycles are unknown, which, in addition to the poor representation of mesoscale features, reduces the reliability of predictions of the future OMZ development in the northern Indian Ocean.
Marion Lagarde, Nolwenn Lemaitre, Hélène Planquette, Mélanie Grenier, Moustafa Belhadj, Pascale Lherminier, and Catherine Jeandel
Biogeosciences, 17, 5539–5561,
Randelle M. Bundy, Alessandro Tagliabue, Nicholas J. Hawco, Peter L. Morton, Benjamin S. Twining, Mariko Hatta, Abigail E. Noble, Mattias R. Cape, Seth G. John, Jay T. Cullen, and Mak A. Saito
Biogeosciences, 17, 4745–4767,Short summary
Cobalt (Co) is an essential nutrient for ocean microbes and is scarce in most areas of the ocean. This study measured Co concentrations in the Arctic Ocean for the first time and found that Co levels are extremely high in the surface waters of the Canadian Arctic. Although the Co primarily originates from the shelf, the high concentrations persist throughout the central Arctic. Co in the Arctic appears to be increasing over time and might be a source of Co to the North Atlantic.
Friedrich A. Burger, Jasmin G. John, and Thomas L. Frölicher
Biogeosciences, 17, 4633–4662,Short summary
Ensemble simulations of an Earth system model reveal that ocean acidity extremes have increased in the past few decades and are projected to increase further in terms of frequency, intensity, duration, and volume extent. The increase is not only caused by the long-term ocean acidification due to the uptake of anthropogenic CO2, but also due to changes in short-term variability. The increase in ocean acidity extremes may enhance the risk of detrimental impacts on marine organisms.
Christopher Gordon, Katja Fennel, Clark Richards, Lynn K. Shay, and Jodi K. Brewster
Biogeosciences, 17, 4119–4134,Short summary
We describe a method for correcting errors in oxygen optode measurements on autonomous platforms in the ocean. The errors result from the relatively slow response time of the sensor. The correction method includes an in situ determination of the effective response time and requires the time stamps of the individual measurements. It is highly relevant for the BGC-Argo program and also applicable to gliders. We also explore if diurnal changes in oxygen can be obtained from profiling floats.
Bin Wang, Katja Fennel, Liuqian Yu, and Christopher Gordon
Biogeosciences, 17, 4059–4074,Short summary
We assess trade-offs between different types of biological observations, specifically satellite ocean color and BGC-Argo profiles and the benefits of combining both for optimizing a biogeochemical model of the Gulf of Mexico. Using all available observations leads to significant improvements in observed and unobserved variables (including primary production and C export). Our results highlight the significant benefits of BGC-Argo measurements for biogeochemical model optimization and validation.
Bruce L. Greaves, Andrew T. Davidson, Alexander D. Fraser, John P. McKinlay, Andrew Martin, Andrew McMinn, and Simon W. Wright
Biogeosciences, 17, 3815–3835,Short summary
We observed that variation in the Southern Annular Mode (SAM) over 11 years showed a relationship with the species composition of hard-shelled phytoplankton in the seasonal ice zone (SIZ) of the Southern Ocean. Phytoplankton in the SIZ are productive during the southern spring and summer when the area is ice-free, with production feeding most Antarctic life. The SAM is known to be increasing with climate change, and changes in phytoplankton in the SIZ may have implications for higher life forms.
Vincent Taillandier, Louis Prieur, Fabrizio D'Ortenzio, Maurizio Ribera d'Alcalà, and Elvira Pulido-Villena
Biogeosciences, 17, 3343–3366,Short summary
This study addresses the role played by vertical diffusion in the nutrient enrichment of the Levantine intermediate waters, a process particularly relevant inside thermohaline staircases. Thanks to a high profiling frequency over a 4-year period, BGC-Argo float observations reveal the temporal continuity of the layering patterns encountered during the cruise PEACETIME and their impact on vertical and lateral transfers of nitrate between the deep reservoir and the surface productive zone.
Coraline Leseurre, Claire Lo Monaco, Gilles Reverdin, Nicolas Metzl, Jonathan Fin, Solveig Olafsdottir, and Virginie Racapé
Biogeosciences, 17, 2553–2577,Short summary
In this study, we investigate the evolution of CO2 uptake and ocean acidification in the North Atlantic Subpolar surface water. Our results show an important reduction in the capacity of the ocean to absorb CO2 from the atmosphere (1993–2007), due to a rapid increase in the fCO2 and associated with a rapid decrease in pH. Conversely, data obtained during the last decade (2008–2017) show a stagnation of fCO2 (increasing the ocean sink for CO2) and pH.
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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.
We investigated the origin and mechanisms of the natural iron fertilization that sustains a...