Articles | Volume 11, issue 23
Biogeosciences, 11, 6683–6696, 2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
the Creative Commons Attribution 3.0 License.
Research article 04 Dec 2014
Research article | 04 Dec 2014
Comparative organic geochemistry of Indian margin (Arabian Sea) sediments: estuary to continental slope
G. Cowie et al.
L. A. Levin, A. L. McGregor, G. F. Mendoza, C. Woulds, P. Cross, U. Witte, A. J. Gooday, G. Cowie, and H. Kitazato
Biogeosciences, 10, 7161–7177,
Swaleha Inamdar, Liselotte Tinel, Rosie Chance, Lucy J. Carpenter, Prabhakaran Sabu, Racheal Chacko, Sarat C. Tripathy, Anvita U. Kerkar, Alok K. Sinha, Parli Venkateswaran Bhaskar, Amit Sarkar, Rajdeep Roy, Tomás Sherwen, Carlos Cuevas, Alfonso Saiz-Lopez, Kirpa Ram, and Anoop S. Mahajan
Atmos. Chem. Phys., 20, 12093–12114,Short summary
Iodine chemistry is generating a lot of interest because of its impacts on the oxidising capacity of the marine boundary and depletion of ozone. However, one of the challenges has been predicting the right levels of iodine in the models, which depend on parameterisations for emissions from the sea surface. This paper discusses the different parameterisations available and compares them with observations, showing that our current knowledge is still insufficient, especially on a regional scale.
Clare Woulds, James B. Bell, Adrian G. Glover, Steven Bouillon, and Louise S. Brown
Biogeosciences, 17, 1–12,Short summary
Sedimented hydrothermal vents occur where heated, mineral-rich (hydrothermal) water seeps through seafloor sediments. They host chemosynthetic microbes, which use chemical energy to fix dissolved carbon dioxide into sugars (chemosynthesis). We conducted carbon tracing experiments, and observed chemosynthesis at both vent and non-vent sites. Thus, chemosynthesis occurred over a much larger area than expected, suggesting it is more widespread than previously thought.
James B. Bell, William D. K. Reid, David A. Pearce, Adrian G. Glover, Christopher J. Sweeting, Jason Newton, and Clare Woulds
Biogeosciences, 14, 5705–5725,Short summary
Sedimented hydrothermal vents are among the least studied deep-sea ecosystems. We compared food webs between hydrothermally active and off-vent areas of the Bransfield Strait, Antarctica. Invertebrates showed diverse feeding strategies and occupied different positions in food webs between vent and non-vent sites. Feeding and microbial diversity was lowest at vent sites. Chemosynthetic organic matter was a minimal food source at both vents and non-vents.
Karoliina A. Koho, Lennart J. de Nooijer, Christophe Fontanier, Takashi Toyofuku, Kazumasa Oguri, Hiroshi Kitazato, and Gert-Jan Reichart
Biogeosciences, 14, 3067–3082,Short summary
Here we report Mn / Ca ratios in living benthic foraminifera from the NE Japan margin. The results show that the Mn incorporation directly reflects the environment where the foraminifera calcify. Foraminifera that live deeper in sediment, under greater redox stress, generally incorporate more Mn into their carbonate skeletons. As such, foraminifera living close to the Mn reduction zone in sediment appear promising tools for paleoceanographic reconstructions of sedimentary redox conditions.
Parvathi Vallivattathillam, Suresh Iyyappan, Matthieu Lengaigne, Christian Ethé, Jérôme Vialard, Marina Levy, Neetu Suresh, Olivier Aumont, Laure Resplandy, Hema Naik, and Wajih Naqvi
Biogeosciences, 14, 1541–1559,Short summary
During late boreal summer and fall, the west coast of India (WCI) experiences hypoxia, which turns into anoxia during some years. We analyze a coupled physical–biogeochemical simulation over the 1960–2012 period to investigate the physical processes influencing oxycline interannual variability off the WCI. We show that fall WCI oxycline fluctuations are strongly related to Indian Ocean Dipole (IOD), with positive IODs preventing anoxia, while negative IODs do not necessarily result in anoxia.
Pratirupa Bardhan, Syed Wajih Ahmad Naqvi, Supriya G. Karapurkar, Damodar M. Shenoy, Siby Kurian, and Hema Naik
Biogeosciences, 14, 767–779,Short summary
Although India has the third highest number of dams globally, there is a knowledge gap on the cycling of bioessential elements in such systems. This study (first of its kind) investigates the stable isotopes of nitrate and particulate organic matter in a pristine Indian reservoir. Nitrogen transformations in the anaerobic bottom waters were isotopically characterised. Overall, solar intensity, water depth and redox conditions are the major controls on the biogeochemical cycling in this system.
James B. Bell, William D. K. Reid, David A. Pearce, Adrian G. Glover, Christopher J. Sweeting, Jason Newton, and Clare Woulds
Revised manuscript not acceptedShort summary
Areas of the deep-seafloor where hydrothermal fluid flows through sediment are amongst the least studied environments on the planet. We studied the faunal and microbial food webs at one such system in the Southern Ocean and found evidence of a wide range of organic matter fixation pathways, both at vent sites and non-vent sites. Although faunal uptake of in situ food production was low, it was much wider spread than previously realised, raising important questions about seafloor food webs.
Clare Woulds, Steven Bouillon, Gregory L. Cowie, Emily Drake, Jack J. Middelburg, and Ursula Witte
Biogeosciences, 13, 4343–4357,Short summary
Estuarine sediments are important locations for carbon cycling and burial. We used tracer experiments to investigate how site conditions affect the way in which seafloor biological communities cycle carbon. We showed that while total respiration rates are primarily determined by temperature, total carbon processing by the biological community is strongly related to its biomass. Further, we saw a distinct pattern of carbon cycling in sandy sediment, in which uptake by bacteria dominates.
K. E. Larkin, A. J. Gooday, C. Woulds, R. M. Jeffreys, M. Schwartz, G. Cowie, C. Whitcraft, L. Levin, J. R. Dick, and D. W. Pond
Biogeosciences, 11, 3729–3738,
A. K. Pratihary, S. W. A. Naqvi, G. Narvenkar, S. Kurian, H. Naik, R. Naik, and B. R. Manjunatha
Biogeosciences, 11, 2771–2791,
K. Banse, S. W. A. Naqvi, P. V. Narvekar, J. R. Postel, and D. A. Jayakumar
Biogeosciences, 11, 2237–2261,
L. A. Levin, A. L. McGregor, G. F. Mendoza, C. Woulds, P. Cross, U. Witte, A. J. Gooday, G. Cowie, and H. Kitazato
Biogeosciences, 10, 7161–7177,
Related subject area
Biogeochemistry: Coastal OceanBiophysical controls on seasonal changes in the structure, growth, and grazing of the size-fractionated phytoplankton community in the northern South China SeaSeasonal dispersal of fjord meltwaters as an important source of iron and manganese to coastal Antarctic phytoplanktonModeling cyanobacteria life cycle dynamics and historical nitrogen fixation in the Baltic ProperSimultaneous assessment of oxygen- and nitrate-based net community production in a temperate shelf sea from a single ocean gliderReviews and syntheses: Physical and biogeochemical processes associated with upwelling in the Indian OceanParticulate organic carbon dynamics in the Gulf of Lion shelf (NW Mediterranean) using a coupled hydrodynamic–biogeochemical modelTechnical note: Novel triple O2 sensor aquatic eddy covariance instrument with improved time shift correction reveals central role of microphytobenthos for carbon cycling in coral reef sandsLong-term spatiotemporal variations in and expansion of low-oxygen conditions in the Pearl River estuary: a study synthesizing observations during 1976–2017Contrasting patterns of carbon cycling and DOM processing in two phytoplankton-bacteria communitiesFe-binding organic ligands in coastal and frontal regions of the western Antarctic PeninsulaTemporal variability and driving factors of the carbonate system in the Aransas Ship Channel, TX, USA: a time series studyNitrogen loss processes in response to upwelling in a Peruvian coastal setting dominated by denitrification – a mesocosm approachRetracing hypoxia in Eckernförde Bight (Baltic Sea)The impact of the freeze–melt cycle of land-fast ice on the distribution of dissolved organic matter in the Laptev and East Siberian seas (Siberian Arctic)The fate of upwelled nitrate off Peru shaped by submesoscale filaments and frontsReviews and Syntheses: Spatial and temporal patterns in metabolic fluxes inform potential for seagrass to locally mitigate ocean acidificationCoastal processes modify projections of some climate-driven stressors in the California Current SystemMixed layer depth dominates over upwelling in regulating the seasonality of ecosystem functioning in the Peruvian Upwelling SystemTemporal dynamics of surface ocean carbonate chemistry in response to natural and simulated upwelling events during the 2017 coastal El Niño near Callao, PeruUpwelling-induced trace gas dynamics in the Baltic Sea inferred from 8 years of autonomous measurements on a ship of opportunityDestruction and reinstatement of coastal hypoxia in the South China Sea off the Pearl River estuaryHypersaline tidal flats as important “blue carbon” systems: a case study from three ecosystemsDrivers and impact of the seasonal variability of the organic carbon offshore transport in the Canary upwelling systemOrganic carbon densities and accumulation rates in surface sediments of the North Sea and SkagerrakAn observation-based evaluation and ranking of historical Earth system model simulations in the northwest North Atlantic OceanCharacterizing the origins of dissolved organic carbon in coastal seawater using stable carbon isotope and light absorption characteristicsWarming and ocean acidification may decrease estuarine dissolved organic carbon export to the oceanChemical characterization of the Punta de Fuencaliente CO2-enriched system (La Palma, NE Atlantic Ocean): a new natural laboratory for ocean acidification studiesThe seasonal phases of an Arctic lagoon reveal the discontinuities of pH variability and CO2 flux at the air–sea interfaceThe northern European shelf as an increasing net sink for CO2Impacts of biogenic polyunsaturated aldehydes on metabolism and community composition of particle-attached bacteria in coastal hypoxiaA Lagrangian study of the contribution of the Canary coastal upwelling to the nitrogen budget of the open North AtlanticDenitrification by benthic foraminifera and their contribution to N-loss from a fjord environmentPelagic primary production in the coastal Mediterranean Sea: variability, trends and contribution to basin scale budgetsA numerical model study of the main factors contributing to hypoxia and its interannual and short-term variability in the East China SeaThe effects of decomposing invasive jellyfish on biogeochemical fluxes and microbial dynamics in an ultra-oligotrophic seaUsing 226Ra and 228Ra isotopes to distinguish water mass distribution in the Canadian Arctic ArchipelagoFactors controlling plankton community production, export flux, and particulate matter stoichiometry in the coastal upwelling system off PeruReconstructing extreme climatic and geochemical conditions during the largest natural mangrove dieback on recordTechnical note: Measurements and data analysis of sediment–water oxygen flux using a new dual-optode eddy covariance instrumentThe impact of intertidal areas on the carbonate system of the southern North SeaThe recent state and variability of the carbonate system of the Canadian Arctic Archipelago and adjacent basins in the context of ocean acidificationA regional hindcast model simulating ecosystem dynamics, inorganic carbon chemistry, and ocean acidification in the Gulf of AlaskaRelative impacts of global changes and regional watershed changes on the inorganic carbon balance of the Chesapeake BayDecoupling of ΔO2∕Ar and particulate organic carbon dynamics in nearshore surface ocean watersWind-driven stratification patterns and dissolved oxygen depletion off the Changjiang (Yangtze) EstuaryRemoval of phosphorus and nitrogen in sediments of the eutrophic Stockholm archipelago, Baltic SeaQuantifying the contributions of riverine vs. oceanic nitrogen to hypoxia in the East China SeaMacroalgal metabolism and lateral carbon flows can create significant carbon sinksRegulation of nitrous oxide production in low-oxygen waters off the coast of Peru
Yuan Dong, Qian P. Li, Zhengchao Wu, Yiping Shuai, Zijia Liu, Zaiming Ge, Weiwen Zhou, and Yinchao Chen
Biogeosciences, 18, 6423–6434,Short summary
Temporal change of plankton growth and grazing are less known in the coastal ocean, not to mention the relevant controlling mechanisms. Here, we performed monthly size-specific dilution experiments outside a eutrophic estuary over a 1-year cycle. Phytoplankton growth was correlated to nutrients and grazing mortality to total chlorophyll a. A selective grazing on small cells may be important for maintaining high abundance of large-chain-forming diatoms in this eutrophic system.
Kiefer O. Forsch, Lisa Hahn-Woernle, Robert M. Sherrell, Vincent J. Roccanova, Kaixuan Bu, David Burdige, Maria Vernet, and Katherine A. Barbeau
Biogeosciences, 18, 6349–6375,Short summary
We show that for an unperturbed cold western Antarctic Peninsula fjord, the seasonality of iron and manganese is linked to the dispersal of metal-rich meltwater sources. Geochemical measurements of trace metals in meltwaters, porewaters, and seawater, collected during two expeditions, showed a seasonal cycle of distinct sources. Finally, model results revealed that the dispersal of surface meltwater and meltwater plumes originating from under the glacier is sensitive to katabatic wind events.
Jenny Hieronymus, Kari Eilola, Malin Olofsson, Inga Hense, H. E. Markus Meier, and Elin Almroth-Rosell
Biogeosciences, 18, 6213–6227,Short summary
Dense blooms of cyanobacteria occur every summer in the Baltic Proper and can add to eutrophication by their ability to turn nitrogen gas into dissolved inorganic nitrogen. Being able to correctly estimate the size of this nitrogen fixation is important for management purposes. In this work, we find that the life cycle of cyanobacteria plays an important role in capturing the seasonality of the blooms as well as the size of nitrogen fixation in our ocean model.
Tom Hull, Naomi Greenwood, Antony Birchill, Alexander Beaton, Matthew Palmer, and Jan Kaiser
Biogeosciences, 18, 6167–6180,Short summary
The shallow shelf seas play a large role in the global cycling of CO2 and also support large fisheries. We use an autonomous underwater vehicle in the central North Sea to measure the rates of change in oxygen and nutrients. Using these data we determine the amount of carbon dioxide taken out of the atmosphere by the sea and measure how productive the region is. These observations will be useful for improving our predictive models and help us predict and adapt to a changing ocean.
Puthenveettil Narayana Menon Vinayachandran, Yukio Masumoto, Michael J. Roberts, Jenny A. Huggett, Issufo Halo, Abhisek Chatterjee, Prakash Amol, Garuda V. M. Gupta, Arvind Singh, Arnab Mukherjee, Satya Prakash, Lynnath E. Beckley, Eric Jorden Raes, and Raleigh Hood
Biogeosciences, 18, 5967–6029,Short summary
Upwelling in the coastal ocean triggers biological productivity and thus enhances fisheries. Therefore, understanding the phenomenon of upwelling and the underlying mechanisms is important. In this paper, the present understanding of the upwelling along the coastline of the Indian Ocean from the coast of Africa all the way up to the coast of Australia is reviewed. The review provides a synthesis of the physical processes associated with upwelling and its impact on the marine ecosystem.
Gaël Many, Caroline Ulses, Claude Estournel, and Patrick Marsaleix
Biogeosciences, 18, 5513–5538,Short summary
The Gulf of Lion shelf is one of the most productive areas in the Mediterranean. A model is used to study the mechanisms that drive the particulate organic carbon (POC). The model reproduces the annual cycle of primary production well. The shelf appears as an autotrophic ecosystem with a high production and as a source of POC for the adjacent basin. The increase in temperature induced by climate change could impact the trophic status of the shelf.
Alireza Merikhi, Peter Berg, and Markus Huettel
Biogeosciences, 18, 5381–5395,Short summary
The aquatic eddy covariance technique is a powerful method for measurements of solute fluxes across the sediment–water interface. Data measured by conventional eddy covariance instruments require a time shift correction that can result in substantial flux errors. We introduce a triple O2 sensor eddy covariance instrument that by design eliminates these errors. Deployments next to a conventional instrument in the Florida Keys demonstrate the improvements achieved through the new design.
Jiatang Hu, Zhongren Zhang, Bin Wang, and Jia Huang
Biogeosciences, 18, 5247–5264,Short summary
In situ observations over 42 years were used to explore the long-term changes to low-oxygen conditions in the Pearl River estuary. Apparent expansion of the low-oxygen conditions in summer was identified, primarily due to the combined effects of increased anthropogenic inputs and decreased sediment load. Large areas of severe low-oxygen events were also observed in early autumn and were formed by distinct mechanisms. The estuary seems to be growing into a seasonal, estuary-wide hypoxic zone.
Samu Markku Elovaara, Eeva Liisa Eronen-Rasimus, Eero Jooseppi Asmala, Tobias Tamelander, and Hermanni Pekka Kaartokallio
Revised manuscript accepted for BGShort summary
Dissolved organic matter (DOM) is a significant carbon pool in the marine environment. The composition of the DOM pool, as well as its interaction with microbes, is complex, yet understanding them is important for understanding global carbon cycling. This study shows that two phytoplankton species have different effects on the composition of the DOM pool and, through the DOM they produce, on the ensuing microbial community. These communities in turn have different effects on DOM composition.
Indah Ardiningsih, Kyyas Seyitmuhammedov, Sylvia G. Sander, Claudine H. Stirling, Gert-Jan Reichart, Kevin R. Arrigo, Loes J. A. Gerringa, and Rob Middag
Biogeosciences, 18, 4587–4601,Short summary
Organic Fe speciation is investigated along a natural gradient of the western Antarctic Peninsula from an ice-covered shelf to the open ocean. The two major fronts in the region affect the distribution of ligands. The excess ligands not bound to dissolved Fe (DFe) comprised up to 80 % of the total ligand concentrations, implying the potential to solubilize additional Fe input. The ligands on the shelf can increase the DFe residence time and fuel local primary production upon ice melt.
Melissa R. McCutcheon, Hongming Yao, Cory J. Staryk, and Xinping Hu
Biogeosciences, 18, 4571–4586,Short summary
We used 5+ years of discrete samples and 10 months of hourly sensor measurements to explore temporal variability and environmental controls on pH and pCO2 at the Aransas Ship Channel. Seasonal and diel variability were both present but small compared to other regions in the literature. Despite the small tidal range, tidal control often surpassed biological control. In comparison with sensor data, discrete samples were generally representative of mean annual and seasonal carbonate chemistry.
Kai G. Schulz, Eric P. Achterberg, Javier Arístegui, Lennart T. Bach, Isabel Baños, Tim Boxhammer, Dirk Erler, Maricarmen Igarza, Verena Kalter, Andrea Ludwig, Carolin Löscher, Jana Meyer, Judith Meyer, Fabrizio Minutolo, Elisabeth von der Esch, Bess B. Ward, and Ulf Riebesell
Biogeosciences, 18, 4305–4320,Short summary
Upwelling of nutrient-rich deep waters to the surface make eastern boundary upwelling systems hot spots of marine productivity. This leads to subsurface oxygen depletion and the transformation of bioavailable nitrogen into inert N2. Here we quantify nitrogen loss processes following a simulated deep water upwelling. Denitrification was the dominant process, and budget calculations suggest that a significant portion of nitrogen that could be exported to depth is already lost in the surface ocean.
Heiner Dietze and Ulrike Löptien
Biogeosciences, 18, 4243–4264,Short summary
In recent years fish-kill events caused by oxygen deficit have been reported in Eckernförde Bight (Baltic Sea). This study sets out to understand the processes causing respective oxygen deficits by combining high-resolution coupled ocean circulation biogeochemical modeling, monitoring data, and artificial intelligence.
Jens A. Hölemann, Bennet Juhls, Dorothea Bauch, Markus Janout, Boris P. Koch, and Birgit Heim
Biogeosciences, 18, 3637–3655,Short summary
The Arctic Ocean receives large amounts of river water rich in terrestrial dissolved organic matter (tDOM), which is an important component of the Arctic carbon cycle. Our analysis shows that mixing of three major freshwater sources is the main factor that regulates the distribution of tDOM concentrations in the Siberian shelf seas. In this context, the formation and melting of the land-fast ice in the Laptev Sea and the peak spring discharge of the Lena River are of particular importance.
Jaard Hauschildt, Soeren Thomsen, Vincent Echevin, Andreas Oschlies, Yonss Saranga José, Gerd Krahmann, Laura A. Bristow, and Gaute Lavik
Biogeosciences, 18, 3605–3629,Short summary
In this paper we quantify the subduction of upwelled nitrate due to physical processes on the order of several kilometers in the coastal upwelling off Peru and its effect on primary production. We also compare the prepresentation of these processes in a high-resolution simulation (~2.5 km) with a more coarsely resolved simulation (~12 km). To do this, we combine high-resolution shipboard observations of physical and biogeochemical parameters with a complex biogeochemical model configuration.
Kristy Kroeker, Tye Kindinger, Heidi Hirsh, Melissa Ward, Tessa Hill, Brittany Jellison, David Koweek, Sarah Lummis, Emily Rivest, George Waldbusser, and Brian Gaylord
Revised manuscript accepted for BGShort summary
Here, we synthesize the results from 62 studies reporting in situ rates of seagrass metabolism to highlight spatial and temporal variability in carbon fluxes and inform efforts to use seagrass to mitigate ocean acidification. Our analyses suggest seagrass meadows are generally autotrophic, variable in space and tie, and the modeled effects on seawater pH are relatively small in magnitude.
Samantha A. Siedlecki, Darren Pilcher, Evan M. Howard, Curtis Deutsch, Parker MacCready, Emily L. Norton, Hartmut Frenzel, Jan Newton, Richard A. Feely, Simone R. Alin, and Terrie Klinger
Biogeosciences, 18, 2871–2890,Short summary
Future ocean conditions can be simulated using projected trends in fossil fuel use paired with Earth system models. Global models generally do not include local processes important to coastal ecosystems. These coastal processes can alter the degree of change projected. Higher-resolution models that include local processes predict modified changes in carbon stressors when compared to changes projected by global models in the California Current System.
Tianfei Xue, Ivy Frenger, A. E. Friederike Prowe, Yonss Saranga José, and Andreas Oschlies
Revised manuscript accepted for BGShort summary
The Peruvian system supports 10 % of the world's fishing yield. In the Peruvian system, wind and earth’s rotation bring cold, nutrient-rich water to the surface and allow phytoplankton to grow. But observations show that it grows worse at high upwelling. Using a model, we find that high upwelling happens when air mixes the water the most. Then phytoplankton is diluted and grows slowly due to low light and cool upwelled water. This study helps to estimate how it might change in a warming climate.
Shao-Min Chen, Ulf Riebesell, Kai G. Schulz, Elisabeth von der Esch, Eric P. Achterberg, and Lennart T. Bach
Revised manuscript accepted for BGShort summary
Oxygen minimum zones in the ocean are characterized by enhanced carbon dioxide (CO2) levels and are being further acidified by increasing anthropogenic atmospheric CO2. Here we report CO2 system measurements in a mesocosm study offshore Peru during a rare coastal El Niño event, to investigate how CO2 dynamics may respond to on-going ocean deoxygenation. Our observations show that nitrogen limitation, productivity and plankton community shift play an important role in driving the CO2 dynamics.
Erik Jacobs, Henry C. Bittig, Ulf Gräwe, Carolyn A. Graves, Michael Glockzin, Jens D. Müller, Bernd Schneider, and Gregor Rehder
Biogeosciences, 18, 2679–2709,Short summary
We use a unique data set of 8 years of continuous carbon dioxide (CO2) and methane (CH4) surface water measurements from a commercial ferry to study upwelling in the Baltic Sea. Its seasonality and regional and interannual variability are examined. Strong upwelling events drastically increase local surface CO2 and CH4 levels and are mostly detected in late summer after long periods of impaired mixing. We introduce an extrapolation method to estimate regional upwelling-induced trace gas fluxes.
Yangyang Zhao, Khanittha Uthaipan, Zhongming Lu, Yan Li, Jing Liu, Hongbin Liu, Jianping Gan, Feifei Meng, and Minhan Dai
Biogeosciences, 18, 2755–2775,Short summary
In situ oxygen consumption rates were estimated for the first time during destruction of coastal hypoxia as disturbed by a typhoon and its reinstatement in the South China Sea off the Pearl River estuary. The reinstatement of summer hypoxia was rapid with a comparable timescale with that of its initial disturbance from frequent tropical cyclones, which has important implications for better understanding the intermittent nature of coastal hypoxia and its prediction in a changing climate.
Dylan R. Brown, Humberto Marotta, Roberta B. Peixoto, Alex Enrich-Prast, Glenda C. Barroso, Mario L. G. Soares, Wilson Machado, Alexander Pérez, Joseph M. Smoak, Luciana M. Sanders, Stephen Conrad, James Z. Sippo, Isaac R. Santos, Damien T. Maher, and Christian J. Sanders
Biogeosciences, 18, 2527–2538,Short summary
Hypersaline tidal flats (HTFs) are coastal ecosystems with freshwater deficits often occurring in arid or semi-arid regions near mangrove supratidal zones with no major fluvial contributions. This study shows that HTFs are important carbon and nutrient sinks which may be significant given their extensive coverage. Our findings highlight a previously unquantified carbon as well as a nutrient sink and suggest that coastal HTF ecosystems could be included in the emerging blue carbon framework.
Giulia Bonino, Elisa Lovecchio, Nicolas Gruber, Matthias Münnich, Simona Masina, and Doroteaciro Iovino
Biogeosciences, 18, 2429–2448,Short summary
Seasonal variations of processes such as upwelling and biological production that happen along the northwestern African coast can modulate the temporal variability of the biological activity of the adjacent open North Atlantic hundreds of kilometers away from the coast thanks to the lateral transport of coastal organic carbon. This happens with a temporal delay, which is smaller than a season up to roughly 500 km from the coast due to the intense transport by small-scale filaments.
Markus Diesing, Terje Thorsnes, and Lilja Rún Bjarnadóttir
Biogeosciences, 18, 2139–2160,Short summary
The upper 10 cm of the seafloor of the North Sea and Skagerrak contain 231×106 t of carbon in organic form. The Norwegian Trough, the deepest sedimentary basin in the studied area, stands out as a zone of strong organic carbon accumulation with rates on par with neighbouring fjords. Conversely, large parts of the North Sea are characterised by rapid organic carbon degradation and negligible accumulation. This dual character is likely typical for continental shelf sediments worldwide.
Arnaud Laurent, Katja Fennel, and Angela Kuhn
Biogeosciences, 18, 1803–1822,Short summary
CMIP5 and CMIP6 models, and a high-resolution regional model, were evaluated by comparing historical simulations with observations in the northwest North Atlantic, a climate-sensitive and biologically productive ocean margin region. Many of the CMIP models performed poorly for biological properties. There is no clear link between model resolution and skill in the global models, but there is an overall improvement in performance in CMIP6 from CMIP5. The regional model performed best.
Heejun Han, Jeomshik Hwang, and Guebuem Kim
Biogeosciences, 18, 1793–1801,Short summary
The main source of excess DOC occurring in coastal seawater off an artificial lake, which is enclosed by a dike along the western coast of South Korea, was determined using a combination of various biogeochemical tools including DOC and nutrient concentrations, stable carbon isotope, and optical properties (absorbance and fluorescence) of dissolved organic matter in two different seasons (March 2017 and September 2018).
Michelle N. Simone, Kai G. Schulz, Joanne M. Oakes, and Bradley D. Eyre
Biogeosciences, 18, 1823–1838,Short summary
Estuaries are responsible for a large contribution of dissolved organic carbon (DOC) to the global C cycle, but it is unknown how this will change in the future. DOC fluxes from unvegetated sediments were investigated ex situ subject to conditions of warming and ocean acidification. The future climate shifted sediment fluxes from a slight DOC source to a significant sink, with global coastal DOC export decreasing by 80 %. This has global implications for C cycling and long-term C storage.
Sara González-Delgado, David González-Santana, Magdalena Santana-Casiano, Melchor González-Dávila, Celso A. Hernández, Carlos Sangil, and José Carlos Hernández
Biogeosciences, 18, 1673–1687,Short summary
We describe the carbon system dynamics of a new CO2 seep system located off the coast of La Palma. We explored for over a year, finding points with lower levels of pH and alkalinity; high levels of carbon; and poorer levels of aragonite and calcite, both essential for calcifying species. The seeps are a key feature for robust experimental designs, aimed at comprehending how life has persisted through past eras or at predicting the consequences of ocean acidification in the marine realm.
Cale A. Miller, Christina Bonsell, Nathan D. McTigue, and Amanda L. Kelley
Biogeosciences, 18, 1203–1221,Short summary
We report here the first year-long high-frequency pH data set for an Arctic lagoon that captures ice-free and ice-covered seasons. pH and salinity correlation varies by year as we observed positive correlation and independence. Photosynthesis is found to drive high pH values, and small changes in underwater solar radiation can result in rapid decreases in pH. We estimate that arctic lagoons may act as sources of CO2 to the atmosphere, potentially offsetting the Arctic Ocean's CO2 sink capacity.
Meike Becker, Are Olsen, Peter Landschützer, Abdirhaman Omar, Gregor Rehder, Christian Rödenbeck, and Ingunn Skjelvan
Biogeosciences, 18, 1127–1147,Short summary
We developed a simple method to refine existing open-ocean maps towards different coastal seas. Using a multi-linear regression, we produced monthly maps of surface ocean fCO2 in the northern European coastal seas (the North Sea, the Baltic Sea, the Norwegian Coast and the Barents Sea) covering a time period from 1998 to 2016. Based on this fCO2 map, we calculate trends in surface ocean fCO2, pH and the air–sea gas exchange.
Zhengchao Wu, Qian P. Li, Zaiming Ge, Bangqin Huang, and Chunming Dong
Biogeosciences, 18, 1049–1065,Short summary
Seasonal hypoxia in the nearshore bottom waters frequently occurs in the Pearl River estuary. Aerobic respiration is the ultimate cause of local hypoxia. We found an elevated level of polyunsaturated aldehydes in the bottom water outside the estuary, which promoted the growth and metabolism of special groups of particle-attached bacteria and thus contributed to oxygen depletion in hypoxic waters. Our results may be important for understanding coastal hypoxia and its linkages to eutrophication.
Derara Hailegeorgis, Zouhair Lachkar, Christoph Rieper, and Nicolas Gruber
Biogeosciences, 18, 303–325,Short summary
Using a Lagrangian modeling approach, this study provides a quantitative analysis of water and nitrogen offshore transport in the Canary Current System. We investigate the timescales, reach and structure of offshore transport and demonstrate that the Canary upwelling is a key source of nutrients to the open North Atlantic Ocean. Our findings stress the need for improving the representation of the Canary system and other eastern boundary upwelling systems in global coarse-resolution models.
Constance Choquel, Emmanuelle Geslin, Edouard Metzger, Helena L. Filipsson, Nils Risgaard-Petersen, Patrick Launeau, Manuel Giraud, Thierry Jauffrais, Bruno Jesus, and Aurélia Mouret
Biogeosciences, 18, 327–341,Short summary
Marine microorganisms such as foraminifera are able to live temporarily without oxygen in sediments. In a Swedish fjord subjected to seasonal oxygen scarcity, a change in fauna linked to the decrease in oxygen and the increase in an invasive species was shown. The invasive species respire nitrate until 100 % of the nitrate porewater in the sediment and could be a major contributor to nitrogen balance in oxic coastal ecosystems. But prolonged hypoxia creates unfavorable conditions to survive.
Paula Maria Salgado-Hernanz, Aurore Regaudie de Gioux, David Antoine, and Gotzon Basterretxea
Revised manuscript accepted for BG
Haiyan Zhang, Katja Fennel, Arnaud Laurent, and Changwei Bian
Biogeosciences, 17, 5745–5761,Short summary
In coastal seas, low oxygen, which is detrimental to coastal ecosystems, is increasingly caused by man-made nutrients from land. This is especially so near mouths of major rivers, including the Changjiang in the East China Sea. Here a simulation model is used to identify the main factors determining low-oxygen conditions in the region. High river discharge is identified as the prime cause, while wind and intrusions of open-ocean water modulate the severity and extent of low-oxygen conditions.
Tamar Guy-Haim, Maxim Rubin-Blum, Eyal Rahav, Natalia Belkin, Jacob Silverman, and Guy Sisma-Ventura
Biogeosciences, 17, 5489–5511,Short summary
The availability of nutrients in oligotrophic marine ecosystems is limited. Following jellyfish blooms, large die-off events result in the release of high amounts of nutrients to the water column and sediment. Our study assessed the decomposition effects of an infamous invasive jellyfish in the ultra-oligotrophic Eastern Mediterranean Sea. We found that jellyfish decomposition favored heterotrophic bacteria and altered biogeochemical fluxes, further impoverishing this nutrient-poor ecosystem.
Chantal Mears, Helmuth Thomas, Paul B. Henderson, Matthew A. Charette, Hugh MacIntyre, Frank Dehairs, Christophe Monnin, and Alfonso Mucci
Biogeosciences, 17, 4937–4959,Short summary
Major research initiatives have been undertaken within the Arctic Ocean, highlighting this area's global importance and vulnerability to climate change. In 2015, the international GEOTRACES program addressed this importance by devoting intense research activities to the Arctic Ocean. Among various tracers, we used radium and carbonate system data to elucidate the functioning and vulnerability of the hydrographic regime of the Canadian Arctic Archipelago, bridging the Pacific and Atlantic oceans.
Lennart Thomas Bach, Allanah Joy Paul, Tim Boxhammer, Elisabeth von der Esch, Michelle Graco, Kai Georg Schulz, Eric Achterberg, Paulina Aguayo, Javier Arístegui, Patrizia Ayón, Isabel Baños, Avy Bernales, Anne Sophie Boegeholz, Francisco Chavez, Gabriela Chavez, Shao-Min Chen, Kristin Doering, Alba Filella, Martin Fischer, Patricia Grasse, Mathias Haunost, Jan Hennke, Nauzet Hernández-Hernández, Mark Hopwood, Maricarmen Igarza, Verena Kalter, Leila Kittu, Peter Kohnert, Jesus Ledesma, Christian Lieberum, Silke Lischka, Carolin Löscher, Andrea Ludwig, Ursula Mendoza, Jana Meyer, Judith Meyer, Fabrizio Minutolo, Joaquin Ortiz Cortes, Jonna Piiparinen, Claudia Sforna, Kristian Spilling, Sonia Sanchez, Carsten Spisla, Michael Sswat, Mabel Zavala Moreira, and Ulf Riebesell
Biogeosciences, 17, 4831–4852,Short summary
The eastern boundary upwelling system off Peru is among Earth's most productive ocean ecosystems, but the factors that control its functioning are poorly constrained. Here we used mesocosms, moored ~ 6 km offshore Peru, to investigate how processes in plankton communities drive key biogeochemical processes. We show that nutrient and light co-limitation keep productivity and export at a remarkably constant level while stoichiometry changes strongly with shifts in plankton community structure.
James Z. Sippo, Isaac R. Santos, Christian J. Sanders, Patricia Gadd, Quan Hua, Catherine E. Lovelock, Nadia S. Santini, Scott G. Johnston, Yota Harada, Gloria Reithmeir, and Damien T. Maher
Biogeosciences, 17, 4707–4726,Short summary
In 2015–2016, a massive mangrove dieback event occurred along ~1000 km of coastline in Australia. Multiple lines of evidence from climate data, wood and sediment samples suggest low water availability within the dead mangrove forest. Wood and sediments also reveal a large increase in iron concentrations in mangrove sediments during the dieback. This study supports the hypothesis that the forest dieback was associated with low water availability driven by a climate-change-related ENSO event.
Markus Huettel, Peter Berg, and Alireza Merikhi
Biogeosciences, 17, 4459–4476,Short summary
Oxygen fluxes are a valued proxy for organic carbon production and mineralization at the seafloor. These fluxes can be measured non-invasively with the aquatic eddy covariance instrument, but the fast, fragile oxygen sensor it uses often causes questionable flux data. We developed a dual-O2-optode instrument and data evaluation method that allow improved flux measurements. Deployments over carbonate sands in the shallow shelf demonstrate that the instrument can produce reliable oxygen flux data.
Fabian Schwichtenberg, Johannes Pätsch, Michael Ernst Böttcher, Helmuth Thomas, Vera Winde, and Kay-Christian Emeis
Biogeosciences, 17, 4223–4245,Short summary
Ocean acidification has a range of potentially harmful consequences for marine organisms. It is related to total alkalinity (TA) mainly produced in oxygen-poor situations like sediments in tidal flats. TA reduces the sensitivity of a water body to acidification. The decomposition of organic material and subsequent TA release in the tidal areas of the North Sea (Wadden Sea) is responsible for reduced acidification in the southern North Sea. This is shown with the results of an ecosystem model.
Alexis Beaupré-Laperrière, Alfonso Mucci, and Helmuth Thomas
Biogeosciences, 17, 3923–3942,Short summary
Ocean acidification is the process by which the oceans are changing due to carbon dioxide emissions from human activities. Studying this process in the Arctic Ocean is essential as this ocean and its ecosystems are more vulnerable to the effects of acidification. Water chemistry measurements made in recent years show that waters in and around the Canadian Arctic Archipelago are considerably affected by this process and show dynamic conditions that might have an impact on local marine organisms.
Claudine Hauri, Cristina Schultz, Katherine Hedstrom, Seth Danielson, Brita Irving, Scott C. Doney, Raphael Dussin, Enrique N. Curchitser, David F. Hill, and Charles A. Stock
Biogeosciences, 17, 3837–3857,Short summary
The coastal ecosystem of the Gulf of Alaska (GOA) is especially vulnerable to the effects of ocean acidification and climate change. To improve our conceptual understanding of the system, we developed a new regional biogeochemical model setup for the GOA. Model output suggests that bottom water is seasonally high in CO2 between June and January. Such extensive periods of reoccurring high CO2 may be harmful to ocean acidification-sensitive organisms.
Pierre St-Laurent, Marjorie A. M. Friedrichs, Raymond G. Najjar, Elizabeth H. Shadwick, Hanqin Tian, and Yuanzhi Yao
Biogeosciences, 17, 3779–3796,Short summary
Over the past century, estuaries have experienced global (atmospheric CO2 concentrations and temperature) and regional changes (river inputs, land use), but their relative impact remains poorly known. In the Chesapeake Bay, we find that global and regional changes have worked together to enhance how much atmospheric CO2 is taken up by the estuary. The increased uptake is roughly equally due to the global and regional changes, providing crucial perspective for managers of the bay's watershed.
Sarah Z. Rosengard, Robert W. Izett, William J. Burt, Nina Schuback, and Philippe D. Tortell
Biogeosciences, 17, 3277–3298,Short summary
Net community production sets the maximum quantity of phytoplankton carbon available for the marine food web and longer-term storage in the deep ocean. We compared two approaches to estimate this critical variable from autonomous measurements of mixed-layer dissolved oxygen and particulate organic carbon, observing a significant discrepancy between estimates in an upwelling zone near the Oregon coast. We use this discrepancy to assess the fate of organic carbon produced in the mixed layer.
Taavi Liblik, Yijing Wu, Daidu Fan, and Dinghui Shang
Biogeosciences, 17, 2875–2895,Short summary
Multiple factors have been accused of triggering coastal hypoxia off the Changjiang Estuary. In situ observations, remote sensing and numerical simulation data were used to study dissolved oxygen depletion in the area. Oxygen distributions can be explained by wind forcing and river discharge, as well as concurrent features in surface and deep layer circulation. If summer monsoon prevails, hypoxia more likely occurs in the north while hypoxia in the south appears if the summer monsoon is weaker.
Niels A. G. M. van Helmond, Elizabeth K. Robertson, Daniel J. Conley, Martijn Hermans, Christoph Humborg, L. Joëlle Kubeneck, Wytze K. Lenstra, and Caroline P. Slomp
Biogeosciences, 17, 2745–2766,Short summary
We studied the removal of phosphorus (P) and nitrogen (N) in the eutrophic Stockholm archipelago (SA). High sedimentation rates and sediment P contents lead to high P burial. Benthic denitrification is the primary nitrate-reducing pathway. Together, these mechanisms limit P and N transport to the open Baltic Sea. We expect that further nutrient load reduction will contribute to recovery of the SA from low-oxygen conditions and that the sediments will continue to remove part of the P and N loads.
Fabian Große, Katja Fennel, Haiyan Zhang, and Arnaud Laurent
Biogeosciences, 17, 2701–2714,Short summary
In the East China Sea, hypoxia occurs frequently from spring to fall due to high primary production and subsequent decomposition of organic matter. Nitrogen inputs from the Changjiang and the open ocean have been suggested to contribute to hypoxia formation. We used a numerical modelling approach to quantify the relative contributions of these nitrogen sources. We found that the Changjiang dominates, which suggests that nitrogen management in the watershed would improve oxygen conditions.
Kenta Watanabe, Goro Yoshida, Masakazu Hori, Yu Umezawa, Hirotada Moki, and Tomohiro Kuwae
Biogeosciences, 17, 2425–2440,Short summary
Macroalgal beds are among the vegetated coastal ecosystems that take up atmospheric CO2. We investigated the relationships between macroalgal metabolism and inorganic and organic carbon fluxes in a temperate macroalgal bed during the productive time of year. The macroalgal metabolism formed water with low CO2 and high dissolved organic carbon concentrations that was then exported offshore. This export process potentially enhances CO2 uptake in and around macroalgal beds.
Claudia Frey, Hermann W. Bange, Eric P. Achterberg, Amal Jayakumar, Carolin R. Löscher, Damian L. Arévalo-Martínez, Elizabeth León-Palmero, Mingshuang Sun, Xin Sun, Ruifang C. Xie, Sergey Oleynik, and Bess B. Ward
Biogeosciences, 17, 2263–2287,Short summary
The production of N2O via nitrification and denitrification associated with low-O2 waters is a major source of oceanic N2O. We investigated the regulation and dynamics of these processes with respect to O2 and organic matter inputs. The transcription of the key nitrification gene amoA rapidly responded to changes in O2 and strongly correlated with N2O production rates. N2O production by denitrification was clearly stimulated by organic carbon, implying that its supply controls N2O production.
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