Articles | Volume 17, issue 8
Research article 22 Apr 2020
Research article | 22 Apr 2020
Spatial variations in silicate-to-nitrate ratios in Southern Ocean surface waters are controlled in the short term by physics rather than biology
Pieter Demuynck et al.
No articles found.
Daisy Pickup and Toby Tyrrell
Revised manuscript not acceptedShort summary
Concentrations of chemical elements dissolved in seawater differ from place to place in the surface ocean. Understanding how they change, and why, is important, for instance to understand ocean carbon storage or to understand nutrient supply for life in the ocean. We used a new global dataset to study spatial changes of numerous elements, many not studied before. We find a common pattern: an increase from low to high latitudes, because deep water rises to the surface at high latitudes.
Angela A. Bahamondes Dominguez, Anna E. Hickman, Robert Marsh, and C. Mark Moore
Geosci. Model Dev., 13, 4019–4040,Short summary
The central Celtic Sea has previously been studied with a 1-D model called S2P3, showing discrepancies between observations and the model results due to poor representation of some processes. Therefore, the S2P3 model was developed to include zooplankton and phytoplankton cells' adaptation to changes in irradiance. Results demonstrate that better agreement with biological observations can be achieved when the model includes these processes and is adequately constrained.
Hannah K. Donald, Gavin L. Foster, Nico Fröhberg, George E. A. Swann, Alex J. Poulton, C. Mark Moore, and Matthew P. Humphreys
Biogeosciences, 17, 2825–2837,Short summary
The boron isotope pH proxy is increasingly being used to reconstruct ocean pH in the past. Here we detail a novel analytical methodology for measuring the boron isotopic composition (δ11B) of diatom opal and apply this to the study of the diatom Thalassiosira weissflogii grown in culture over a range of pH. To our knowledge this is the first study of its kind and provides unique insights into the way in which diatoms incorporate boron and their potential as archives of palaeoclimate records.
Jan D. Zika, Jean-Baptiste Sallée, Andrew J. S. Meijers, Alberto C. Naveira-Garabato, Andrew J. Watson, Marie-Jose Messias, and Brian A. King
Ocean Sci., 16, 323–336,Short summary
The ocean can regulate climate by distributing heat and carbon dioxide into its interior. This work has resulted from a major experiment aimed at understanding how that distribution occurs. In the experiment an artificial tracer was released into the ocean. After release the tracer was tracked as it was distorted by ocean currents. Using novel methods we reveal how the tracer's distortions follow the movement of the underlying water masses in the ocean and we estimate the rate at which it mixes.
Frances E. Hopkins, Philip D. Nightingale, John A. Stephens, C. Mark Moore, Sophie Richier, Gemma L. Cripps, and Stephen D. Archer
Biogeosciences, 17, 163–186,Short summary
We investigated the effects of ocean acidification (OA) on the production of climate active gas dimethylsulfide (DMS) in polar waters. We found that polar DMS production was unaffected by OA – in contrast to temperate waters, where large increases in DMS occurred. The regional differences in DMS response may reflect natural variability in community adaptation to ambient carbonate chemistry and should be taken into account in predicting the influence of future DMS emissions on Earth's climate.
Alexander Forryan, Sheldon Bacon, Takamasa Tsubouchi, Sinhué Torres-Valdés, and Alberto C. Naveira Garabato
The Cryosphere, 13, 2111–2131,Short summary
We compare control volume and geochemical tracer-based methods of estimating the Arctic Ocean freshwater budget and find both methods in good agreement. Inconsistencies arise from the distinction between
Pacificwaters in the geochemical calculations. The definition of Pacific waters is particularly problematic due to the non-conservative nature of the nutrients underpinning the definition and the low salinity characterizing waters entering the Arctic through Bering Strait.
Chris J. Daniels, Alex J. Poulton, William M. Balch, Emilio Marañón, Tim Adey, Bruce C. Bowler, Pedro Cermeño, Anastasia Charalampopoulou, David W. Crawford, Dave Drapeau, Yuanyuan Feng, Ana Fernández, Emilio Fernández, Glaucia M. Fragoso, Natalia González, Lisa M. Graziano, Rachel Heslop, Patrick M. Holligan, Jason Hopkins, María Huete-Ortega, David A. Hutchins, Phoebe J. Lam, Michael S. Lipsen, Daffne C. López-Sandoval, Socratis Loucaides, Adrian Marchetti, Kyle M. J. Mayers, Andrew P. Rees, Cristina Sobrino, Eithne Tynan, and Toby Tyrrell
Earth Syst. Sci. Data, 10, 1859–1876,Short summary
Calcifying marine algae (coccolithophores) are key to oceanic biogeochemical processes, such as calcium carbonate production and export. We compile a global database of calcium carbonate production from field samples (n = 2756), alongside primary production rates and coccolithophore abundance. Basic statistical analysis highlights global distribution, average surface and integrated rates, patterns with depth and the importance of considering cell-normalised rates as a simple physiological index.
M. Dolores Pérez-Hernández, Alonso Hernández-Guerra, Isis Comas-Rodríguez, Verónica M. Benítez-Barrios, Eugenio Fraile-Nuez, Josep L. Pelegrí, and Alberto C. Naveira Garabato
Ocean Sci., 13, 577–587,Short summary
The decadal differences between the ALBATROSS (April 1999) and MOC2-Austral (February 2010) hydrographic cruises are analyzed. Changes in the intermediate water masses beneath seem to be very sensitive to the wind conditions existing in their formation area. The Subantarctic Front is wider and weaker in 2010 than in 1999, while the Polar Front remains in the same position and strengthens.
Anastasia Charalampopoulou, Alex J. Poulton, Dorothee C. E. Bakker, Mike I. Lucas, Mark C. Stinchcombe, and Toby Tyrrell
Biogeosciences, 13, 5917–5935,Short summary
Coccolithophores are global calcifiers, potentially impacted by ocean acidity. Data from the Southern Ocean is scarce, though latitudinal gradients of acidity exist. We made measurements of calcification, species composition and physiochemical environment between America and the Antarctic Peninsula. Calcification and cell calcite declined to the south, though rates of coccolith production did not. Declining temperature and irradiance were more important in driving latitudinal changes than pH.
C. J. Daniels, A. J. Poulton, M. Esposito, M. L. Paulsen, R. Bellerby, M. St John, and A. P. Martin
Biogeosciences, 12, 2395–2409,
B. A. Kelly-Gerreyn, A. P. Martin, B. J. Bett, T. R. Anderson, J. I. Kaariainen, C. E. Main, C. J. Marcinko, and A. Yool
Biogeosciences, 11, 6401–6416,
J. R. Young, A. J. Poulton, and T. Tyrrell
Biogeosciences, 11, 4771–4782,
S. Richier, E. P. Achterberg, C. Dumousseaud, A. J. Poulton, D. J. Suggett, T. Tyrrell, M. V. Zubkov, and C. M. Moore
Biogeosciences, 11, 4733–4752,
M. Ribas-Ribas, V. M. C. Rérolle, D. C. E. Bakker, V. Kitidis, G. A. Lee, I. Brown, E. P. Achterberg, N. J. Hardman-Mountford, and T. Tyrrell
Biogeosciences, 11, 4339–4355,
S. Torres Valdés, S. C. Painter, A. P. Martin, R. Sanders, and J. Felden
Earth Syst. Sci. Data, 6, 123–145,
Related subject area
Biogeochemistry: Open OceanImpact 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 sectionComparing CLE-AdCSV applications using SA and TAC to determine the Fe binding characteristics of model ligands in seawaterCarbon 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 approachPhosphorus cycling in the upper waters of the Mediterranean Sea (Peacetime cruise): relative contribution of external and internal sourcesImpact of dust addition on the metabolism of Mediterranean plankton communities and carbon export under present and future conditions of pH and temperatureOn 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 isotopesLong distance particle transport to the central Ionian SeaAssimilating 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 OceanInfluence of atmospheric deposition on biogeochemical cycles in an oligotrophic ocean systemParticulate 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)Characterizing the surface microlayer in the Mediterranean Sea: trace metal concentrations and microbial plankton abundancePhytoplankton and dimethylsulfide dynamics at two contrasting Arctic ice edgesExperiment design and bacterial abundance control extracellular H2O2 concentrations during four series of mesocosm experimentsDissolved iron in the North Atlantic Ocean and Labrador Sea along the GEOVIDE section (GEOTRACES section GA01)No nitrogen fixation in the Bay of Bengal?Trends and decadal oscillations of oxygen and nutrients at 50 to 300 m depth in the equatorial and North PacificPhysical drivers of the nitrate seasonal variability in the Atlantic cold tongueCoccolithophore biodiversity controls carbonate export in the Southern OceanArctic (Svalbard islands) active and exported diatom stocks and cell health statusHow will the key marine calcifier Emiliania huxleyi respond to a warmer and more thermally variable ocean?Ideas and perspectives: Is dark carbon fixation relevant for oceanic primary production estimates?Sensitivity of ocean biogeochemistry to the iron supply from the Antarctic Ice Sheet explored with a biogeochemical modelIsotopic fractionation of carbon during uptake by phytoplankton across the South Atlantic subtropical convergenceThe effect of marine aggregate parameterisations on nutrients and oxygen minimum zones in a global biogeochemical modelSensitivity of atmospheric CO2 to regional variability in particulate organic matter remineralization depthsNutrient distribution and nitrogen and oxygen isotopic composition of nitrate in water masses of the subtropical southern Indian OceanWhat drives the latitudinal gradient in open-ocean surface dissolved inorganic carbon concentration?Investigating the effect of El Niño on nitrous oxide distribution in the eastern tropical South PacificReciprocal bias compensation and ensuing uncertainties in model-based climate projections: pelagic biogeochemistry versus ocean mixing
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.
Loes J. A. Gerringa, Martha Gledhill, Indah Ardiningsih, Niels Muntjewerf, and Luis M. Laglera
Revised manuscript accepted for BGShort summary
For three decades, competitive ligand exchange-adsorptive cathodic stripping voltammetry was used to estimate the Fe-binding capacity of organic matter in seawater. In this manuscript the performance of the competing ligands is compared trough the analysis of a series of model ligands. The main finding of this manuscript 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.
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.
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
Revised manuscript under review for BGShort summary
High sensitive phosphate measurements in the Mediterranean Sea allowed detecting vertical gradients of phosphate concentration above the phosphacline. Estimated phosphate fluxes from below were comparable to atmospheric deposition except under the influence of rain and Saharan dust. Taken together, external sources of phosphate contributed little to total phosphate requirements which were mainly sustained by enzymatic hydrolysis of the organic phosphorus pool.
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
Revised manuscript accepted for BGShort 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.
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.
Léo Berline, Andrea Michelangelo Doglioli, Anne Petrenko, Stéphanie Barrillon, Boris Espinasse, Frederic A. C. Le Moigne, François Simon-Bot, Melilotus Thyssen, and François Carlotti
Preprint under review for BGShort summary
While Ionian Sea is considered as 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 relatively short distance. Using remote sensing and Lagrangian simulations, we suggest that this contrast originate from long distance transport of particles from the north, west and east of Ionian Sea, where phytoplankton production was more intense.
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.
France Van Wambeke, Vincent Taillandier, Karine Deboeufs, Elvira Pulido-Villena, Julie Dinasquet, Anja Engel, Emilio Marañón, Céline Ridame, and Cécile Guieu
Revised manuscript under review for BGShort summary
Simultaneous in situ measurements of (dry and wet) atmospheric deposition, and biogeochemical stocks and fluxes in the sunlight waters of the open Mediterranean Sea revealed complex physical and biological processes. Dry N deposition contributed moderately to the N biological demand in the mixed layer (11 % for primary producers, 27 % for heterotrophic bacteria). The transitory effect observed after a wet dust deposition impacted the microbial food web down to the DCM.
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.
Antonio Tovar-Sánchez, Araceli Rodríguez-Romero, Anja Engel, Birthe Zäncker, Franck Fu, Emilio Marañón, María Pérez-Lorenzo, Matthieu Bressac, Thibaut Wagener, Sylvain Triquet, Guillaume Siour, Karine Desboeufs, and Cécile Guieu
Biogeosciences, 17, 2349–2364,Short summary
Residence times of particulate metals derived from aerosol deposition in the Sea Surface Microlayer of the Mediterranean Sea ranged from a couple of minutes (e.g., for Fe) to a few hours (e.g., for Cu). Microbial activity seems to play an important role in in this process and in the concentration and distribution of metals between diferent water layers.
Martine Lizotte, Maurice Levasseur, Virginie Galindo, Margaux Gourdal, Michel Gosselin, Jean-Éric Tremblay, Marjolaine Blais, Joannie Charette, and Rachel Hussherr
Biogeosciences, 17, 1557–1581,Short summary
This study brings further support to the premise that the prevalence of younger and thinner icescapes over older and thicker ones in the Canadian High Arctic favors the early development of under-ice microorganisms as well as their production of the climate-relevant gas dimethylsulfide (DMS). Given the rapid rate of climate-driven changes in Arctic sea ice, our results suggest implications for the timing and magnitude of DMS pulses in the Arctic, with ramifications for climate forecasting.
Mark J. Hopwood, Nicolas Sanchez, Despo Polyviou, Øystein Leiknes, Julián Alberto Gallego-Urrea, Eric P. Achterberg, Murat V. Ardelan, Javier Aristegui, Lennart Bach, Sengul Besiktepe, Yohann Heriot, Ioanna Kalantzi, Tuba Terbıyık Kurt, Ioulia Santi, Tatiana M. Tsagaraki, and David Turner
Biogeosciences, 17, 1309–1326,Short summary
Hydrogen peroxide, H2O2, is formed naturally in sunlight-exposed water by photochemistry. At high concentrations it is undesirable to biological cells because it is a stressor. Here, across a range of incubation experiments in diverse marine environments (Gran Canaria, the Mediterranean, Patagonia and Svalbard), we determine that two factors consistently affect the H2O2 concentrations irrespective of geographical location: bacteria abundance and experiment design.
Manon Tonnard, Hélène Planquette, Andrew R. Bowie, Pier van der Merwe, Morgane Gallinari, Floriane Desprez de Gésincourt, Yoan Germain, Arthur Gourain, Marion Benetti, Gilles Reverdin, Paul Tréguer, Julia Boutorh, Marie Cheize, François Lacan, Jan-Lukas Menzel Barraqueta, Leonardo Pereira-Contreira, Rachel Shelley, Pascale Lherminier, and Géraldine Sarthou
Biogeosciences, 17, 917–943,Short summary
We investigated the spatial distribution of dissolved Fe during spring 2014, in order to understand the processes influencing the biogeochemical cycle in the North Atlantic. Our results highlighted elevated Fe close to riverine inputs at the Iberian Margin and glacial inputs at the Newfoundland and Greenland margins. Atmospheric deposition appeared to be a minor source of Fe. Convection was an important source of Fe in the Irminger Sea, which was depleted in Fe relative to nitrate.
Carolin R. Löscher, Wiebke Mohr, Hermann W. Bange, and Donald E. Canfield
Biogeosciences, 17, 851–864,Short summary
Oxygen minimum zones (OMZs) are ocean areas severely depleted in oxygen as a result of physical, chemical, and biological processes. Biologically, organic material is produced in the sea surface and exported to deeper waters, where it respires. In the Bay of Bengal (BoB), an OMZ is present, but there are traces of oxygen left. Our study now suggests that this is because one key process, nitrogen fixation, is absent in the BoB, thus preventing primary production and consecutive respiration.
Lothar Stramma, Sunke Schmidtko, Steven J. Bograd, Tsuneo Ono, Tetjana Ross, Daisuke Sasano, and Frank A. Whitney
Biogeosciences, 17, 813–831,Short summary
The influence of climate signals in the Pacific, especially the Pacific Decadal Oscillation and the North Pacific Gyre Oscillation, as well as El Niño–La Niña and an 18.6-year nodal tidal cycle on oxygen and nutrient trends is investigated. At different locations in the Pacific Ocean different climate signals dominate. Hence, not only trends related to warming but also the influence of climate signals need to be investigated to understand oxygen and nutrient changes in the ocean.
Marie-Hélène Radenac, Julien Jouanno, Christine Carine Tchamabi, Mesmin Awo, Bernard Bourlès, Sabine Arnault, and Olivier Aumont
Biogeosciences, 17, 529–545,Short summary
Satellite data and a remarkable set of in situ measurements show a main bloom of microscopic seaweed, the phytoplankton, in summer and a secondary bloom in December in the central equatorial Atlantic. They are driven by a strong vertical supply of nitrate in May–July and a shorter and moderate supply in November. In between, transport of low-nitrate water from the west explains most nitrate losses in the sunlit layer. Horizontal eddy-induced processes also contribute to seasonal nitrate removal.
Andrés S. Rigual Hernández, Thomas W. Trull, Scott D. Nodder, José A. Flores, Helen Bostock, Fátima Abrantes, Ruth S. Eriksen, Francisco J. Sierro, Diana M. Davies, Anne-Marie Ballegeer, Miguel A. Fuertes, and Lisa C. Northcote
Biogeosciences, 17, 245–263,Short summary
Coccolithophores account for a major fraction of the carbonate produced in the world's oceans. However, their contribution in the subantarctic Southern Ocean remains undocumented. We quantitatively partition calcium carbonate fluxes amongst coccolithophore species in the Australian–New Zealand sector of the Southern Ocean. We provide new insights into the importance of species other than Emiliania huxleyi in the carbon cycle and assess their possible response to projected environmental change.
Susana Agustí, Jeffrey W. Krause, Israel A. Marquez, Paul Wassmann, Svein Kristiansen, and Carlos M. Duarte
Biogeosciences, 17, 35–45,Short summary
We found that 24 % of the total diatoms community in the Arctic water column (450 m depth) was located below the photic layer. Healthy diatom communities in active spring–bloom stages remained in the photic layer. Dying diatom communities exported a large fraction of the biomass to the aphotic zone, fuelling carbon sequestration and benthic ecosystems in the Arctic. The results of the study conform to a conceptual model where diatoms grow during the bloom until silicic acid stocks are depleted.
Xinwei Wang, Feixue Fu, Pingping Qu, Joshua D. Kling, Haibo Jiang, Yahui Gao, and David A. Hutchins
Biogeosciences, 16, 4393–4409,Short summary
In this study, we examine the responses of E. huxleyi to a future warmer and more thermally variable ocean. Elevated temperatures and thermal variation have negative effects on growth rate and physiology that are especially pronounced at high temperatures, but high-frequency thermal variation may reduce the risk of extreme high-temperature events. These findings have potentially large implications for ocean productivity and marine biogeochemical cycles under a future changing climate.
Federico Baltar and Gerhard J. Herndl
Biogeosciences, 16, 3793–3799,Short summary
Around half of the global primary production (PP) is produced in the ocean. Here we quantified how much oceanic PP estimates would increase if we included the dark DIC fixation rates (which are usually excluded in the carbon-14 method) into the PP estimation. We found that the inclusion of dark DIC fixation would increase PP estimates by 5–22 %. This represents ca. 1.2 to 11 Pg C yr−1 of newly synthesized organic carbon available for the marine food web.
Renaud Person, Olivier Aumont, Gurvan Madec, Martin Vancoppenolle, Laurent Bopp, and Nacho Merino
Biogeosciences, 16, 3583–3603,Short summary
The Antarctic Ice Sheet is considered a possibly important but largely overlooked source of iron (Fe). Here we explore its fertilization capacity by evaluating the response of marine biogeochemistry to Fe release from icebergs and ice shelves in a global ocean model. Large regional impacts are simulated, leading to only modest primary production and carbon export increases at the scale of the Southern Ocean. Large uncertainties are due to low observational constraints on modeling choices.
Robyn E. Tuerena, Raja S. Ganeshram, Matthew P. Humphreys, Thomas J. Browning, Heather Bouman, and Alexander P. Piotrowski
Biogeosciences, 16, 3621–3635,Short summary
The carbon isotopes in algae can be used to predict food sources and environmental change. We explore how dissolved carbon is taken up by algae in the South Atlantic Ocean and how this affects their carbon isotope signature. We find that cell size controls isotope fractionation. We use our results to investigate how climate change may impact the carbon isotopes in algae. We suggest a shift to smaller algae in this region would decrease the carbon isotope ratio at the base of the food web.
Daniela Niemeyer, Iris Kriest, and Andreas Oschlies
Biogeosciences, 16, 3095–3111,Short summary
Recent studies suggest spatial variations of the marine particle flux length scale. Using a global biogeochemical ocean model, we investigate whether changes in particle size and size-dependent sinking can explain this variation. We address uncertainties by varying aggregate properties and circulation. Both aspects have an impact on the representation of nutrients, oxygen and oxygen minimum zones. The formation and sinking of large aggregates in productive areas lead to deeper flux penetration.
Jamie D. Wilson, Stephen Barker, Neil R. Edwards, Philip B. Holden, and Andy Ridgwell
Biogeosciences, 16, 2923–2936,Short summary
The remains of plankton rain down from the surface ocean to the deep ocean, acting to store CO2 in the deep ocean. We used a model of biology and ocean circulation to explore the importance of this process in different regions of the ocean. The amount of CO2 stored in the deep ocean is most sensitive to changes in the Southern Ocean. As plankton in the Southern Ocean are likely those most impacted by future climate change, the amount of CO2 they store in the deep ocean could also be affected.
Natalie C. Harms, Niko Lahajnar, Birgit Gaye, Tim Rixen, Kirstin Dähnke, Markus Ankele, Ulrich Schwarz-Schampera, and Kay-Christian Emeis
Biogeosciences, 16, 2715–2732,Short summary
The Indian Ocean subtropical gyre is a large oligotrophic area that is likely to adjust to continued warming by increasing stratification, reduced nutrient supply and decreasing biological production. In this study, we investigated concentrations of nutrients and stable isotopes of nitrate. We determine the lateral influence of water masses entering the gyre from the northern Indian Ocean and from the Southern Ocean and quantify the input of nitrogen by N2 fixation into the surface layer.
Yingxu Wu, Mathis P. Hain, Matthew P. Humphreys, Sue Hartman, and Toby Tyrrell
Biogeosciences, 16, 2661–2681,Short summary
This study takes advantage of the GLODAPv2 database to investigate the processes driving the surface ocean dissolved inorganic carbon distribution, with the focus on its latitudinal gradient between the polar oceans and the low-latitude oceans. Based on our quantitative study, we find that temperature-driven CO2 gas exchange and high-latitude upwelling of DIC- and TA-rich deep waters are the two major drivers, with the importance of the latter not having been previously realized.
Qixing Ji, Mark A. Altabet, Hermann W. Bange, Michelle I. Graco, Xiao Ma, Damian L. Arévalo-Martínez, and Damian S. Grundle
Biogeosciences, 16, 2079–2093,Short summary
A strong El Niño event occurred in the Peruvian coastal region in 2015–2016, during which higher sea surface temperatures co-occurred with significantly lower sea-to-air fluxes of nitrous oxide, an important greenhouse gas and ozone depletion agent. Stratified water column during El Niño retained a larger amount of nitrous oxide that was produced via multiple microbial pathways; and intense nitrous oxide effluxes could occur when normal upwelling is resumed after El Niño.
Ulrike Löptien and Heiner Dietze
Biogeosciences, 16, 1865–1881,Short summary
Anthropogenic greenhouse gas emissions trigger complex climate feedbacks. Output form Earth system models provides a basis for related political decision-making. One challenge is to arrive at reliable model parameter estimates for the ocean biogeochemistry module. We illustrate pitfalls through which flaws in the ocean module are masked by wrongly tuning the biogeochemistry and discuss ensuing uncertainties in climate projections.
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The availability of macronutrients N and Si is of key importance to sustain life in the Southern Ocean. N and Si are available in abundance at the southern boundary of the Southern Ocean due to constant supply from the deep ocean. In the more northern regions of the Southern Ocean, a decline in macronutrient concentration is noticed, especially strong for Si rather than N. This paper uses a simplified biogeochemical model to investigate processes responsible for this decline in concentration.
The availability of macronutrients N and Si is of key importance to sustain life in the Southern...