Articles | Volume 10, issue 4
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.
the Creative Commons Attribution 3.0 License.
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.
the Creative Commons Attribution 3.0 License.
Coccolithophore surface distributions in the North Atlantic and their modulation of the air-sea flux of CO2 from 10 years of satellite Earth observation data
J. D. Shutler
Plymouth Marine Laboratory, Plymouth, UK
P. E. Land
Plymouth Marine Laboratory, Plymouth, UK
C. W. Brown
Center for Satellite Applications and Research, National Oceanic and Atmospheric Administration, USA
H. S. Findlay
Plymouth Marine Laboratory, Plymouth, UK
C. J. Donlon
European Space Agency, ESA/ESTEC, Noordwijk, the Netherlands
Plymouth Marine Laboratory, Plymouth, UK
College of Life and Environmental Sciences, University of Exeter, UK
J. C. Blackford
Plymouth Marine Laboratory, Plymouth, UK
Related subject area
Biogeochemistry: Air - Sea ExchangeConcentrations of dissolved dimethyl sulfide (DMS), methanethiol and other trace gases in context of microbial communities from the temperate Atlantic to the Arctic OceanMarine nitrogen fixation as a possible source of atmospheric water-soluble organic nitrogen aerosols in the subtropical North PacificIce nucleating properties of the sea ice diatom Fragilariopsis cylindrus and its exudatesOn physical mechanisms enhancing air–sea CO2 exchangeWinter season Southern Ocean distributions of climate-relevant trace gasesHow biogenic polymers control surfactant dynamics in the surface microlayer: insights from a coastal Baltic Sea studyIdentifying the biological control of the annual and multi-year variations in South Atlantic air–sea CO2 fluxThe sensitivity of pCO2 reconstructions to sampling scales across a Southern Ocean sub-domain: a semi-idealized ocean sampling simulation approachPhysical mechanisms for biological carbon uptake during the onset of the spring phytoplankton bloom in the northwestern Mediterranean Sea (BOUSSOLE site)Air-sea gas exchange in a seagrass ecosystemWintertime process study of the North Brazil Current rings reveals the region as a larger sink for CO2 than expectedNew constraints on biological production and mixing processes in the South China Sea from triple isotope composition of dissolved oxygenTidal mixing of estuarine and coastal waters in the western English Channel is a control on spatial and temporal variability in seawater CO2A seamless ensemble-based reconstruction of surface ocean pCO2 and air–sea CO2 fluxes over the global coastal and open oceansSea ice concentration impacts dissolved organic gases in the Canadian ArcticEvaluating the Arabian Sea as a regional source of atmospheric CO2: seasonal variability and driversAn empirical MLR for estimating surface layer DIC and a comparative assessment to other gap-filling techniques for ocean carbon time seriesDerivation of seawater pCO2 from net community production identifies the South Atlantic Ocean as a CO2 sourceEukaryotic community composition in the sea surface microlayer across an east–west transect in the Mediterranean SeaEnhancement of the North Atlantic CO2 sink by Arctic WatersGlobal ocean dimethyl sulfide climatology estimated from observations and an artificial neural networkAtmospheric deposition of organic matter at a remote site in the central Mediterranean Sea: implications for the marine ecosystemUnderway seawater and atmospheric measurements of volatile organic compounds in the Southern OceanDimethylsulfide (DMS), marine biogenic aerosols and the ecophysiology of coral reefsSpatial variations in CO2 fluxes in the Saguenay Fjord (Quebec, Canada) and results of a water mixing modelGas exchange estimates in the Peruvian upwelling regime biased by multi-day near-surface stratificationInsights from year-long measurements of air–water CH4 and CO2 exchange in a coastal environmentOn the role of climate modes in modulating the air–sea CO2 fluxes in eastern boundary upwelling systemsReviews and syntheses: the GESAMP atmospheric iron deposition model intercomparison studyIncrease of dissolved inorganic carbon and decrease in pH in near-surface waters in the Mediterranean Sea during the past two decadesUtilizing the Drake Passage Time-series to understand variability and change in subpolar Southern Ocean pCO2Effect of wind speed on the size distribution of gel particles in the sea surface microlayer: insights from a wind–wave channel experimentThe seasonal cycle of pCO2 and CO2 fluxes in the Southern Ocean: diagnosing anomalies in CMIP5 Earth system modelsMarine phytoplankton stoichiometry mediates nonlinear interactions between nutrient supply, temperature, and atmospheric CO2Interannual drivers of the seasonal cycle of CO2 in the Southern OceanConstraints on global oceanic emissions of N2O from observations and modelsArctic Ocean CO2 uptake: an improved multiyear estimate of the air–sea CO2 flux incorporating chlorophyll a concentrationsUncertainty in the global oceanic CO2 uptake induced by wind forcing: quantification and spatial analysisPhytoplankton growth response to Asian dust addition in the northwest Pacific Ocean versus the Yellow SeaGlobal high-resolution monthly pCO2 climatology for the coastal ocean derived from neural network interpolationChanges in the partial pressure of carbon dioxide in the Mauritanian–Cap Vert upwelling region between 2005 and 2012Impact of ocean acidification on Arctic phytoplankton blooms and dimethyl sulfide concentration under simulated ice-free and under-ice conditionsCoral reef origins of atmospheric dimethylsulfide at Heron Island, southern Great Barrier Reef, AustraliaBioavailable atmospheric phosphorous supply to the global ocean: a 3-D global modeling studyCoastal-ocean uptake of anthropogenic carbonRole of zooplankton dynamics for Southern Ocean phytoplankton biomass and global biogeochemical cyclesSurfactant control of gas transfer velocity along an offshore coastal transect: results from a laboratory gas exchange tankClimate impacts on multidecadal pCO2 variability in the North Atlantic: 1948–2009The organic sea-surface microlayer in the upwelling region off the coast of Peru and potential implications for air–sea exchange processesThe impact of sedimentary alkalinity release on the water column CO2 system in the North Sea
Valérie Gros, Bernard Bonsang, Roland Sarda-Estève, Anna Nikolopoulos, Katja Metfies, Matthias Wietz, and Ilka Peeken
Biogeosciences, 20, 851–867,Short summary
The oceans are both sources and sinks for trace gases important for atmospheric chemistry and marine ecology. Here, we quantified selected trace gases (including the biological metabolites dissolved dimethyl sulfide, methanethiol and isoprene) along a 2500 km transect from the North Atlantic to the Arctic Ocean. In the context of phytoplankton and bacterial communities, our study suggests that methanethiol (rarely measured before) might substantially influence ocean–atmosphere cycling.
Tsukasa Dobashi, Yuzo Miyazaki, Eri Tachibana, Kazutaka Takahashi, Sachiko Horii, Fuminori Hashihama, Saori Yasui-Tamura, Yoko Iwamoto, Shu-Kuan Wong, and Koji Hamasaki
Biogeosciences, 20, 439–449,Short summary
Water-soluble organic nitrogen (WSON) in marine aerosols is important for biogeochemical cycling of bioelements. Our shipboard measurements suggested that reactive nitrogen produced and exuded by nitrogen-fixing microorganisms in surface seawater likely contributed to the formation of WSON aerosols in the subtropical North Pacific. This study provides new implications for the role of marine microbial activity in the formation of WSON aerosols in the ocean surface.
Lukas Eickhoff, Maddalena Bayer-Giraldi, Naama Reicher, Yinon Rudich, and Thomas Koop
Biogeosciences, 20, 1–14,Short summary
The formation of ice is an important process in Earth’s atmosphere, biosphere, and cryosphere, in particular in polar regions. Our research focuses on the influence of the sea ice diatom Fragilariopsis cylindrus and of molecules produced by it upon heterogenous ice nucleation. For that purpose, we studied the freezing of tiny droplets containing the diatoms in a microfluidic device. Together with previous studies, our results suggest a common freezing behaviour of various sea ice diatoms.
Lucía Gutiérrez-Loza, Erik Nilsson, Marcus B. Wallin, Erik Sahlée, and Anna Rutgersson
Biogeosciences, 19, 5645–5665,Short summary
The exchange of CO2 between the ocean and the atmosphere is an essential aspect of the global carbon cycle and is highly relevant for the Earth's climate. In this study, we used 9 years of in situ measurements to evaluate the temporal variability in the air–sea CO2 fluxes in the Baltic Sea. Furthermore, using this long record, we assessed the effect of atmospheric and water-side mechanisms controlling the efficiency of the air–sea CO2 exchange under different wind-speed conditions.
Li Zhou, Dennis Booge, Miming Zhang, and Christa A. Marandino
Biogeosciences, 19, 5021–5040,Short summary
Trace gas air–sea exchange exerts an important control on air quality and climate, especially in the Southern Ocean (SO). Almost all of the measurements there are skewed to summer, but it is essential to expand our measurement database over greater temporal and spatial scales. Therefore, we report measured concentrations of dimethylsulfide (DMS, as well as related sulfur compounds) and isoprene in the Atlantic sector of the SO. The observations of isoprene are the first in the winter in the SO.
Theresa Barthelmeß and Anja Engel
Biogeosciences, 19, 4965–4992,Short summary
Greenhouse gases released by human activity cause a global rise in mean temperatures. While scientists can predict how much of these gases accumulate in the atmosphere based on not only human-derived sources but also oceanic sinks, it is rather difficult to predict the major influence of coastal ecosystems. We provide a detailed study on the occurrence, composition, and controls of substances that suppress gas exchange. We thus help to determine what controls coastal greenhouse gas fluxes.
Daniel J. Ford, Gavin H. Tilstone, Jamie D. Shutler, and Vassilis Kitidis
Biogeosciences, 19, 4287–4304,Short summary
This study explores the seasonal, inter-annual, and multi-year drivers of the South Atlantic air–sea CO2 flux. Our analysis showed seasonal sea surface temperatures dominate in the subtropics, and the subpolar regions correlated with biological processes. Inter-annually, the El Niño–Southern Oscillation correlated with the CO2 flux by modifying sea surface temperatures and biological activity. Long-term trends indicated an important biological contribution to changes in the air–sea CO2 flux.
Laique M. Djeutchouang, Nicolette Chang, Luke Gregor, Marcello Vichi, and Pedro M. S. Monteiro
Biogeosciences, 19, 4171–4195,Short summary
Based on observing system simulation experiments using a mesoscale-resolving model, we found that to significantly improve uncertainties and biases in carbon dioxide (CO2) mapping in the Southern Ocean, it is essential to resolve the seasonal cycle (SC) of the meridional gradient of CO2 through high frequency (at least daily) observations that also span the region's meridional axis. We also showed that the estimated SC anomaly and mean annual CO2 are highly sensitive to seasonal sampling biases.
Liliane Merlivat, Michael Hemming, Jacqueline Boutin, David Antoine, Vincenzo Vellucci, Melek Golbol, Gareth A. Lee, and Laurence Beaumont
Biogeosciences, 19, 3911–3920,Short summary
We use in situ high-temporal-resolution measurements of dissolved inorganic carbon and atmospheric parameters at the air–sea interface to analyse phytoplankton bloom initiation identified as the net rate of biological carbon uptake in the Mediterranean Sea. The shift from wind-driven to buoyancy-driven mixing creates conditions for blooms to begin. Active mixing at the air–sea interface leads to the onset of the surface phytoplankton bloom due to the relaxation of wind speed following storms.
Ryo Dobashi and David T. Ho
Seagrass meadows are productive ecosystems and bury much carbon. Understanding their role in the global carbon cycle requires knowledge of air-sea CO2 fluxes and hence the knowledge of gas transfer velocity (k). In this study, k was determined from the dual tracer technique in Florida Bay. The observed gas transfer velocity was lower than previous studies in the coastal and open oceans at the same wind speeds, most likely due to wave attenuation by seagrass and limited wind fetch in this area.
Léa Olivier, Jacqueline Boutin, Gilles Reverdin, Nathalie Lefèvre, Peter Landschützer, Sabrina Speich, Johannes Karstensen, Matthieu Labaste, Christophe Noisel, Markus Ritschel, Tobias Steinhoff, and Rik Wanninkhof
Biogeosciences, 19, 2969–2988,Short summary
We investigate the impact of the interactions between eddies and the Amazon River plume on the CO2 air–sea fluxes to better characterize the ocean carbon sink in winter 2020. The region is a strong CO2 sink, previously underestimated by a factor of 10 due to a lack of data and understanding of the processes responsible for the variability in ocean carbon parameters. The CO2 absorption is mainly driven by freshwater from the Amazon entrained by eddies and by the winter seasonal cooling.
Hana Jurikova, Osamu Abe, Fuh-Kwo Shiah, and Mao-Chang Liang
Biogeosciences, 19, 2043–2058,Short summary
We studied the isotopic composition of oxygen dissolved in seawater in the South China Sea. This tells us about the origin of oxygen in the water column, distinguishing between biological oxygen produced by phytoplankton communities and atmospheric oxygen entering seawater through gas exchange. We found that the East Asian Monsoon plays an important role in determining the amount of oxygen produced vs. consumed by the phytoplankton, as well as in inducing vertical water mass mixing.
Richard P. Sims, Michael Bedington, Ute Schuster, Andrew J. Watson, Vassilis Kitidis, Ricardo Torres, Helen S. Findlay, James R. Fishwick, Ian Brown, and Thomas G. Bell
Biogeosciences, 19, 1657–1674,Short summary
The amount of carbon dioxide (CO2) being absorbed by the ocean is relevant to the earth's climate. CO2 values in the coastal ocean and estuaries are not well known because of the instrumentation used. We used a new approach to measure CO2 across the coastal and estuarine zone. We found that CO2 and salinity were linked to the state of the tide. We used our CO2 measurements and model salinity to predict CO2. Previous studies overestimate how much CO2 the coastal ocean draws down at our site.
Thi Tuyet Trang Chau, Marion Gehlen, and Frédéric Chevallier
Biogeosciences, 19, 1087–1109,Short summary
Air–sea CO2 fluxes and associated uncertainty over the open ocean to coastal shelves are estimated with a new ensemble-based reconstruction of pCO2 trained on observation-based data. The regional distribution and seasonality of CO2 sources and sinks are consistent with those suggested in previous studies as well as mechanisms discussed therein. The ensemble-based uncertainty field allows identifying critical regions where improvements in pCO2 and air–sea CO2 flux estimates should be a priority.
Charel Wohl, Anna E. Jones, William T. Sturges, Philip D. Nightingale, Brent Else, Brian J. Butterworth, and Mingxi Yang
Biogeosciences, 19, 1021–1045,Short summary
We measured concentrations of five different organic gases in seawater in the high Arctic during summer. We found higher concentrations near the surface of the water column (top 5–10 m) and in areas of partial ice cover. This suggests that sea ice influences the concentrations of these gases. These gases indirectly exert a slight cooling effect on the climate, and it is therefore important to measure the levels accurately for future climate predictions.
Alain de Verneil, Zouhair Lachkar, Shafer Smith, and Marina Lévy
Biogeosciences, 19, 907–929,Short summary
The Arabian Sea is a natural CO2 source to the atmosphere, but previous work highlights discrepancies between data and models in estimating air–sea CO2 flux. In this study, we use a regional ocean model, achieve a flux closer to available data, and break down the seasonal cycles that impact it, with one result being the great importance of monsoon winds. As demonstrated in a meta-analysis, differences from data still remain, highlighting the great need for further regional data collection.
Jesse M. Vance, Kim Currie, John Zeldis, Peter W. Dillingham, and Cliff S. Law
Biogeosciences, 19, 241–269,Short summary
Long-term monitoring is needed to detect changes in our environment. Time series of ocean carbon have aided our understanding of seasonal cycles and provided evidence for ocean acidification. Data gaps are inevitable, yet no standard method for filling gaps exists. We present a regression approach here and compare it to seven other common methods to understand the impact of different approaches when assessing seasonal to climatic variability in ocean carbon.
Daniel J. Ford, Gavin H. Tilstone, Jamie D. Shutler, and Vassilis Kitidis
Biogeosciences, 19, 93–115,Short summary
This study identifies the most accurate biological proxy for the estimation of seawater pCO2 fields, which are key to assessing the ocean carbon sink. Our analysis shows that the net community production (NCP), the balance between photosynthesis and respiration, was more accurate than chlorophyll a within a neural network scheme. The improved pCO2 estimates, based on NCP, identified the South Atlantic Ocean as a net CO2 source, compared to a CO2 sink using chlorophyll a.
Birthe Zäncker, Michael Cunliffe, and Anja Engel
Biogeosciences, 18, 2107–2118,Short summary
Fungi are found in numerous marine environments. Our study found an increased importance of fungi in the Ionian Sea, where bacterial and phytoplankton counts were reduced, but organic matter was still available, suggesting fungi might benefit from the reduced competition from bacteria in low-nutrient, low-chlorophyll (LNLC) regions.
Jon Olafsson, Solveig R. Olafsdottir, Taro Takahashi, Magnus Danielsen, and Thorarinn S. Arnarson
Biogeosciences, 18, 1689–1701,Short summary
The Atlantic north of 50° N is an intense ocean sink area for atmospheric CO2. Observations in the vicinity of Iceland reveal a previously unrecognized Arctic contribution to the North Atlantic CO2 sink. Sustained CO2 influx to waters flowing from the Arctic Ocean is linked to their excess alkalinity derived from sources in the changing Arctic. The results relate to the following question: will the North Atlantic continue to absorb CO2 in the future as it has in the past?
Wei-Lei Wang, Guisheng Song, François Primeau, Eric S. Saltzman, Thomas G. Bell, and J. Keith Moore
Biogeosciences, 17, 5335–5354,Short summary
Dimethyl sulfide, a volatile compound produced as a byproduct of marine phytoplankton activity, can be emitted to the atmosphere via gas exchange. In the atmosphere, DMS is oxidized to cloud condensation nuclei, thus contributing to cloud formation. Therefore, oceanic DMS plays an important role in regulating the planet's climate by influencing the radiation budget. In this study, we use an artificial neural network model to update the global DMS climatology and estimate the sea-to-air flux.
Yuri Galletti, Silvia Becagli, Alcide di Sarra, Margherita Gonnelli, Elvira Pulido-Villena, Damiano M. Sferlazzo, Rita Traversi, Stefano Vestri, and Chiara Santinelli
Biogeosciences, 17, 3669–3684,Short summary
This paper reports the first data about atmospheric deposition of dissolved organic matter (DOM) on the island of Lampedusa. It also shows the implications for the surface marine layer by studying the impact of atmospheric organic carbon deposition in the marine ecosystem. It is a preliminary study, but it is pioneering and important for having new data that can be crucial in order to understand the impact of atmospheric deposition on the marine carbon cycle in a global climate change scenario.
Charel Wohl, Ian Brown, Vassilis Kitidis, Anna E. Jones, William T. Sturges, Philip D. Nightingale, and Mingxi Yang
Biogeosciences, 17, 2593–2619,Short summary
The oceans represent a poorly understood source of organic carbon to the atmosphere. In this paper, we present ship-based measurements of specific compounds in ambient air and seawater of the Southern Ocean. We present fluxes of these gases between air and sea at very high resolution. The data also contain evidence for day and night variations in some of these compounds. These measurements can be used to better understand the role of the Southern Ocean in the cycling of these compounds.
Rebecca L. Jackson, Albert J. Gabric, Roger Cropp, and Matthew T. Woodhouse
Biogeosciences, 17, 2181–2204,Short summary
Coral reefs are a strong source of atmospheric sulfur through stress-induced emissions of dimethylsulfide (DMS). This biogenic sulfur can influence aerosol and cloud properties and, consequently, the radiative balance over the ocean. DMS emissions may therefore help to mitigate coral physiological stress via increased low-level cloud cover and reduced sea surface temperature. The importance of DMS in coral physiology and climate is reviewed and the implications for coral bleaching are discussed.
Louise Delaigue, Helmuth Thomas, and Alfonso Mucci
Biogeosciences, 17, 547–566,Short summary
This paper reports on the first compilation and analysis of the surface water pCO2 distribution in the Saguenay Fjord, the southernmost subarctic fjord in the Northern Hemisphere, and thus fills a significant knowledge gap in current regional estimates of estuarine CO2 emissions.
Tim Fischer, Annette Kock, Damian L. Arévalo-Martínez, Marcus Dengler, Peter Brandt, and Hermann W. Bange
Biogeosciences, 16, 2307–2328,Short summary
We investigated air–sea gas exchange in oceanic upwelling regions for the case of nitrous oxide off Peru. In this region, routine concentration measurements from ships at 5 m or 10 m depth prove to overestimate surface (bulk) concentration. Thus, standard estimates of gas exchange will show systematic error. This is due to very shallow stratified layers that inhibit exchange between surface water and waters below and can exist for several days. Maximum bias occurs in moderate wind conditions.
Mingxi Yang, Thomas G. Bell, Ian J. Brown, James R. Fishwick, Vassilis Kitidis, Philip D. Nightingale, Andrew P. Rees, and Timothy J. Smyth
Biogeosciences, 16, 961–978,Short summary
We quantify the emissions and uptake of the greenhouse gases carbon dioxide and methane from the coastal seas of the UK over 1 year using the state-of-the-art eddy covariance technique. Our measurements show how these air–sea fluxes vary twice a day (tidal), diurnally (circadian) and seasonally. We also estimate the air–sea gas transfer velocity, which is essential for modelling and predicting coastal air-sea exchange.
Riley X. Brady, Nicole S. Lovenduski, Michael A. Alexander, Michael Jacox, and Nicolas Gruber
Biogeosciences, 16, 329–346,
Stelios Myriokefalitakis, Akinori Ito, Maria Kanakidou, Athanasios Nenes, Maarten C. Krol, Natalie M. Mahowald, Rachel A. Scanza, Douglas S. Hamilton, Matthew S. Johnson, Nicholas Meskhidze, Jasper F. Kok, Cecile Guieu, Alex R. Baker, Timothy D. Jickells, Manmohan M. Sarin, Srinivas Bikkina, Rachel Shelley, Andrew Bowie, Morgane M. G. Perron, and Robert A. Duce
Biogeosciences, 15, 6659–6684,Short summary
The first atmospheric iron (Fe) deposition model intercomparison is presented in this study, as a result of the deliberations of the United Nations Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP; http://www.gesamp.org/) Working Group 38. We conclude that model diversity over remote oceans reflects uncertainty in the Fe content parameterizations of dust aerosols, combustion aerosol emissions and the size distribution of transported aerosol Fe.
Liliane Merlivat, Jacqueline Boutin, David Antoine, Laurence Beaumont, Melek Golbol, and Vincenzo Vellucci
Biogeosciences, 15, 5653–5662,Short summary
The fugacity of carbon dioxide in seawater (fCO2) was measured hourly in the surface waters of the NW Mediterranean Sea during two 3-year sequences separated by 18 years. A decrease of pH of 0.0022 yr−1 was computed. About 85 % of the accumulation of dissolved inorganic carbon (DIC) comes from chemical equilibration with increasing atmospheric CO2; the remaining 15 % accumulation is consistent with estimates of transfer of Atlantic waters through the Gibraltar Strait.
Amanda R. Fay, Nicole S. Lovenduski, Galen A. McKinley, David R. Munro, Colm Sweeney, Alison R. Gray, Peter Landschützer, Britton B. Stephens, Taro Takahashi, and Nancy Williams
Biogeosciences, 15, 3841–3855,Short summary
The Southern Ocean is highly under-sampled and since this region dominates the ocean sink for CO2, understanding change is critical. Here we utilize available observations to evaluate how the seasonal cycle, variability, and trends in surface ocean carbon in the well-sampled Drake Passage region compare to that of the broader subpolar Southern Ocean. Results indicate that the Drake Passage is representative of the broader region; however, additional winter observations would improve comparisons.
Cui-Ci Sun, Martin Sperling, and Anja Engel
Biogeosciences, 15, 3577–3589,Short summary
Biogenic gel particles such as transparent exopolymer particles (TEP) and Coomassie stainable particles (CSP) are important components in the sea-surface microlayer (SML). Their potential role in air–sea gas exchange and in primary organic aerosol emission has generated considerable research interest. Our wind wave channel experiment revealed how wind speed controls the accumulation and size distribution of biogenic gel particles in the SML.
N. Precious Mongwe, Marcello Vichi, and Pedro M. S. Monteiro
Biogeosciences, 15, 2851–2872,Short summary
Here we analyze seasonal cycle of CO2 biases in 10 CMIP5 models in the SO. We find two main model biases; exaggeration of primary production such that biologically driven DIC changes mainly regulates FCO2 variability, and an overestimation of the role of solubility, such that changes in temperature dominantly drive FCO2 seasonal changes to an extent of opposing biological CO2 uptake in spring. CMIP5 models show greater zonal homogeneity in the seasonal cycle of FCO2 than observational products.
Allison R. Moreno, George I. Hagstrom, Francois W. Primeau, Simon A. Levin, and Adam C. Martiny
Biogeosciences, 15, 2761–2779,Short summary
To bridge the missing links between variable marine elemental stoichiometry, phytoplankton physiology and carbon cycling, we embed four environmentally controlled stoichiometric models into a five-box ocean model. As predicted each model varied in its influence on the biological pump. Surprisingly, we found that variation can lead to nonlinear controls on atmospheric CO2 and carbon export, suggesting the need for further studies of ocean C : P and the impact on ocean carbon cycling.
Luke Gregor, Schalk Kok, and Pedro M. S. Monteiro
Biogeosciences, 15, 2361–2378,Short summary
The Southern Ocean accounts for a large portion of the variability in oceanic CO2 uptake. However, the drivers of these changes are not understood due to a lack of observations. In this study, we used an ensemble of gap-filling methods to estimate surface CO2. We found that winter was a more important driver of longer-term variability driven by changes in wind stress. Summer variability of CO2 was driven primarily by increases in primary production.
Erik T. Buitenhuis, Parvadha Suntharalingam, and Corinne Le Quéré
Biogeosciences, 15, 2161–2175,Short summary
Thanks to decreases in CFC concentrations, N2O is now the third-most important greenhouse gas, and the dominant contributor to stratospheric ozone depletion. Here we estimate the ocean–atmosphere N2O flux. We find that an estimate based on observations alone has a large uncertainty. By combining observations and a range of model simulations we find that the uncertainty is much reduced to 2.45 ± 0.8 Tg N yr−1, and better constrained and at the lower end of the estimate in the latest IPCC report.
Sayaka Yasunaka, Eko Siswanto, Are Olsen, Mario Hoppema, Eiji Watanabe, Agneta Fransson, Melissa Chierici, Akihiko Murata, Siv K. Lauvset, Rik Wanninkhof, Taro Takahashi, Naohiro Kosugi, Abdirahman M. Omar, Steven van Heuven, and Jeremy T. Mathis
Biogeosciences, 15, 1643–1661,Short summary
We estimated monthly air–sea CO2 fluxes in the Arctic Ocean and its adjacent seas north of 60° N from 1997 to 2014, after mapping pCO2 in the surface water using a self-organizing map technique. The addition of Chl a as a parameter enabled us to improve the estimate of pCO2 via better representation of its decline in spring. The uncertainty in the CO2 flux estimate was reduced, and a net annual Arctic Ocean CO2 uptake of 180 ± 130 Tg C y−1 was determined to be significant.
Alizée Roobaert, Goulven G. Laruelle, Peter Landschützer, and Pierre Regnier
Biogeosciences, 15, 1701–1720,
Chao Zhang, Huiwang Gao, Xiaohong Yao, Zongbo Shi, Jinhui Shi, Yang Yu, Ling Meng, and Xinyu Guo
Biogeosciences, 15, 749–765,Short summary
This study compares the response of phytoplankton growth in the northwest Pacific to those in the Yellow Sea. In general, larger positive responses of phytoplankton induced by combined nutrients (in the subtropical gyre of the northwest Pacific) than those induced by a single nutrient (in the Kuroshio Extension and the Yellow Sea) from the dust are observed. We also emphasize the importance of an increase in bioavailable P stock for phytoplankton growth following dust addition.
Goulven G. Laruelle, Peter Landschützer, Nicolas Gruber, Jean-Louis Tison, Bruno Delille, and Pierre Regnier
Biogeosciences, 14, 4545–4561,
Melchor González-Dávila, J. Magdalena Santana Casiano, and Francisco Machín
Biogeosciences, 14, 3859–3871,Short summary
The Mauritanian–Cap Vert upwelling is shown to be sensitive to climate change forcing on upwelling processes, which strongly affects the CO2 surface distribution, ocean acidification rates, and air–sea CO2 exchange. We confirmed an upwelling intensification, an increase in the CO2 outgassing, and an important decrease in the pH of the surface waters. Upwelling areas are poorly studied and VOS lines are shown as one of the most significant contributors to our knowledge of the ocean's response.
Rachel Hussherr, Maurice Levasseur, Martine Lizotte, Jean-Éric Tremblay, Jacoba Mol, Helmuth Thomas, Michel Gosselin, Michel Starr, Lisa A. Miller, Tereza Jarniková, Nina Schuback, and Alfonso Mucci
Biogeosciences, 14, 2407–2427,Short summary
This study assesses the impact of ocean acidification on phytoplankton and its synthesis of the climate-active gas dimethyl sulfide (DMS), as well as its modulation, by two contrasting light regimes in the Arctic. The light regimes tested had no significant impact on either the phytoplankton or DMS concentration, whereas both variables decreased linearly with the decrease in pH. Thus, a rapid decrease in surface water pH could alter the algal biomass and inhibit DMS production in the Arctic.
Hilton B. Swan, Graham B. Jones, Elisabeth S. M. Deschaseaux, and Bradley D. Eyre
Biogeosciences, 14, 229–239,Short summary
We measured the sulfur gas dimethylsulfide (DMS) in marine air at a coral cay on the Great Barrier Reef. DMS is well known to be released from the world's oceans, but environmental evidence of coral reefs releasing DMS has not been clearly demonstrated. We showed the coral reef can sometimes release DMS to the air, which was seen as spikes above the DMS released from the ocean. The DMS from the reef supplements the DMS from the ocean to assist formation of clouds that influence local climate.
Stelios Myriokefalitakis, Athanasios Nenes, Alex R. Baker, Nikolaos Mihalopoulos, and Maria Kanakidou
Biogeosciences, 13, 6519–6543,Short summary
The global atmospheric cycle of P is simulated accounting for natural and anthropogenic sources, acid dissolution of dust aerosol and changes in atmospheric acidity. Simulations show that P-containing dust dissolution flux may have increased in the last 150 years but is expected to decrease in the future, and biological particles are important carriers of bioavailable P to the ocean. These insights to the P cycle have important implications for marine ecosystem responses to climate change.
Timothée Bourgeois, James C. Orr, Laure Resplandy, Jens Terhaar, Christian Ethé, Marion Gehlen, and Laurent Bopp
Biogeosciences, 13, 4167–4185,Short summary
The global coastal ocean took up 0.1 Pg C yr−1 of anthropogenic carbon during 1993–2012 based on new biogeochemical simulations with an eddying 3-D global model. That is about half of the most recent estimate, an extrapolation based on surface areas. It should not be confused with the continental shelf pump, perhaps 10 times larger, which includes natural as well as anthropogenic carbon. Coastal uptake of anthropogenic carbon is limited by its offshore transport.
Corinne Le Quéré, Erik T. Buitenhuis, Róisín Moriarty, Séverine Alvain, Olivier Aumont, Laurent Bopp, Sophie Chollet, Clare Enright, Daniel J. Franklin, Richard J. Geider, Sandy P. Harrison, Andrew G. Hirst, Stuart Larsen, Louis Legendre, Trevor Platt, I. Colin Prentice, Richard B. Rivkin, Sévrine Sailley, Shubha Sathyendranath, Nick Stephens, Meike Vogt, and Sergio M. Vallina
Biogeosciences, 13, 4111–4133,Short summary
We present a global biogeochemical model which incorporates ecosystem dynamics based on the representation of ten plankton functional types, and use the model to assess the relative roles of iron vs. grazing in determining phytoplankton biomass in the Southern Ocean. Our results suggest that observed low phytoplankton biomass in the Southern Ocean during summer is primarily explained by the dynamics of the Southern Ocean zooplankton community, despite iron limitation of phytoplankton growth.
R. Pereira, K. Schneider-Zapp, and R. C. Upstill-Goddard
Biogeosciences, 13, 3981–3989,Short summary
Understanding controls of air–sea gas exchange is necessary for predicting regional- and global-scale trace gas fluxes and feedbacks. Recent studies demonstrated the importance of surfactants, which occur naturally in the uppermost layer of coastal water bodies, to suppress the gas transfer velocity (kw). Here we present data for seawater samples collected from the North Sea. Using a novel analytical approach we show a strong seasonal and spatial relationship between natural surfactants and kw.
Melissa L. Breeden and Galen A. McKinley
Biogeosciences, 13, 3387–3396,Short summary
Natural variability of the North Atlantic carbon cycle is modeled for 1948–2009. The dominant mode of surface ocean CO2 variability is associated with sea surface temperature (SST) variability composed of (a) the Atlantic Multidecadal Oscillation (AMO) and (b) a positive SST trend. In the subpolar gyre, positive AMO is associated with reduced vertical mixing that lowers pCO2. In the subtropical gyre, AMO-associated warming increases pCO2. Since 1980, the SST trend has amplified AMO impacts.
Anja Engel and Luisa Galgani
Biogeosciences, 13, 989–1007,Short summary
The sea-surface microlayer (SML) is a very thin layer at the interface between the ocean and the atmosphere. Organic compounds in the SML may influence the exchange of gases between seawater and air, as well as primary aerosol emission. Here, we report results from the SOPRAN M91 cruise, a field study to the coastal upwelling regime off Peru's coast in 2012. Our study provides novel insight to the relationship between plankton productivity, wind speed and organic matter accumulation in the SML.
H. Brenner, U. Braeckman, M. Le Guitton, and F. J. R. Meysman
Biogeosciences, 13, 841–863,Short summary
Alkalinity released from sediments of the southern North Sea can play an important role in the carbon cycle of the North Sea by lowering the pCO2 of the seawater and thus increasing the CO2 flux between the atmosphere and the water. However, not every single mole alkalinity generated in sediments leads to an additional CO2 uptake, as certain reactions in the water column can negate the respective alkalinity release.
Balch, W. M., Holligan, P. M., Ackleson, S. G., and Voss, K. J.: Biological and optical properties of mesosclae coccolithophore blooms in the Gulf of Maine, Limnol. Oceanogr., 36, 629–643, 1991.
Balch, W. M., Holligan, P. M., and Kilpatrick, K. A.: Calcification, photosynthesis and growth of the bloom forming cocoolithophore, Emiliania huxleyi, Cont. Shelf Res., 12, 1353–1374, 1992.
Balch, W. M., Kilpatrick, K. A., Holligan, P. M., Harbour, D., and Fernandez, E.: The 1991 coccolithophore bloom in the central north Atlantic. II Relating optics to coccolith concentration, Limnol. Oceanogr., 41, 1684–1696, 1996.
Balch, W. M., Gordon, H. R., Bowler, B. C., Drapeau, D. T., and Booth, E. S.: Calcium carbonate measurements in the surface global ocean based on Moderate-Resolution Imaging Spectroradiometer data, J. Geophys. Res., 110, https://doi.org/10.1029/2004JC002560, 2005.
Berelson, W. M., Balch, W. M., Najjar, R. G., Feely, R. A., Sabine, C., and Lee, K.: Relating estimates of CaCO3 production, export and dissolution in the water column to measurements of CaCO3 rain into sediment traps and dissolution on the sea floor: A revised global carbonate budget, Global Biogeochem. Cy., 21, 15, https://doi.org/10.1029/2006GB002803, 2007.
Boyce, D. G., Lewis, M. R., and Worm, B.: Global phytoplankton decline over the past century, Nature, 466, 591–596, 2010.
Brown, C. W. and Yoder, J. A.: Coccolithorid blooms in the global ocean, J. Geophys. Res., 99, 7467–7482, 1994a.
Brown, C. W. and Yoder, J. A.: The distribution pattern of coccolithophorid blooms in the western North Atlantic, Cont. Shelf Res., 14, 175–198, 1994b.
Buitenhuis, E., Van Bleijswijk, J., Bakker, D. C. E., and Veldhuis, M.: Trends in inorganic and organic carbon in a bloom of Emiliania huxleyi in the North Sea, Mar. Ecol. Prog. Ser., 143, 271–282, 1996.
Cokacar, T., Kubilay, N., and Oguz, T.: Structure of Emiliania huxleyi blooms in the Black Sea surface waters as detected by SeaWiFS imagery, Geophys. Res. Lett., 28, 4607–4610, 2001.
Dickson, A. G., Sabine, C., and Christian, J. R.: Guide to best practices for ocean CO2 measurements, PICES Special Publication, 3, 1–191, 2007.
DOE: Handbook of methods for the analysis of the various parameters of the carbon dioxide system in sea water, edited by: Dickson, A. G., and Goyet, C., Department of Energy, 1994.
Frankignoulle, M. and Gattuso, J.-P.: A complete set of buffer factors for acid/base CO2 system in seawater, J. Mar. Syst., 5, 111–118, 1994.
Fromentin, J. M. and Planque, B.: Calanus and environment in the eastern North Atlantic. Influence of the North Atlantic Oscillation on C. finmarchicus and C. helgolandicus, Mar. Ecol. Prog. Ser., 134, 111–118, 1996.
Gattuso, J.-P., Pichon, M., and Frankignoulle, M.: Biological control of air-sea CO2 fluxes: Effect of photosynthetic and calcifying marine organisms and ecosystems, Mar. Ecol. Prog. Ser., 129, 307–312, 1995.
Harlay, J., Borges, A. V., Van Der Zee, C., Delille, B., Godoi, R. H. M., Schiettecatte, L.-S., Roevros, N., Aerts, K., Lapernat, P.-E., Rebreanu, L., Groom, S. B., Daro, R., Van Grieken, M.-H., and Chou, L.: Biogeochemical study of a coccolithophorid bloom in the northern, Bay of Biscay (NE Atlantic Ocean) in June 2004, Prog. Oceanogr., 86, 317–336, 2010.
Holligan, P., Viollier, M., Harbour, D. S., Camus, P., and Champagne-Philippe, M.: Satellite and ship studies of coccolithophore production along a continental shelf edge, Nature, 304, 339–342, https://doi.org/10.1038/304339a0, 1983.
Holligan, P., Fernandez, E., Aiken, J. A., Balch, W. M., Boyd, P., Burkill, P. H., Finch, M., Groom, S. B., Malin, G., Muller, K., Purdie, D. A., Robinson, C., Trees, C., Turner, S. M., and Wal, P. v. d.: A biogeochemical study of the coccolithophore Emiliania huxleyi in the North Atlantic, Global Biogeochem. Cy., 7, 879–900, 1993.
Honjo, S., Manganini, S. J., Krishfield, R. A., and Francois, R.: Particulate organic carbon fluxes to the ocean interior and factors controlling the biological pump: a synthesis of global sediment trap programs since 1983, Prog. Oceanogr., 76, 217–285, 2008.
Hooker, S. B., Zibordi, G., Berthon, J.-F., A'Alimonte, D., Maritorena, S., McLean, S., and Sildam, J.: Results of second SeaWiFS Data Analysis Round Robin, March 2000 (DARR-00), SeaWiFS Project Postlaunch Technical Report Series, 15, 75, 2001.
Hurrell, J. W., Yochanan, K., and Visbeck, M.: The North Atlantic Oscilation, Science, 291, 603–605, 2001.
Hurrell, J. W.: North Atlantic Oscillation data determined using Principal Component Analysis of sea-level pressure, http://www.cgd.ucar.edu/cas/jhurrell/, 2011.
Iglesias-Rodriguez, M. D., Brown, C. W., Doney, S. C., Kleypas, J., Kolber, D., Kolber, Z., Hayes, P. K., and Falkowski, P. G.: Representing key phytoplankton functional groups in ocean carbon cycle models: Coccolithophorids, Global Biogeochem. Cy., 16, 1100, https://doi.org/10.1029/2001GB001454, 2002.
Lavigne, H., and Gattuso, J.-P.: seacarb seawater carbonate chemistry with R, http://CRAN.R-project.org/package=seacarb, 2011.
Le Quere, C., Raupach, M. R., Canadell, J. G., Marland, G., Bopp, L., Ciais, P., Conway, T. J., Doney, S. C., Feely, R. A., Foster, P., Friedlingstein, P., Gurney, K., Houghton, R. A., House, J. I., Huntingford, C., Levy, P. E., Lomas, M. R., Majkut, J., Metzl, N., Ometto, J. P., Peters, G. P., Prentice, I. C., Randerson, J. T., Running, S. W., Sarmiento, J. L., Schuster, U., Sitch, S., Takahashi, T., Viovy, N., van der Werf, G. R., and Woodward, F. I.: Trends in the sources and sinks of carbon dioxide, Nat. Geosci., 2, 831–836, 2009.
Lee, K.: Global net community production estimated from the annual cycle of surface water total dissolved inorganic carbon, Limnol. Oceanogr., 46, 1287–1297, 2001.
Lefevre, N., Watson, A. J., Rios, A. F., Perez, F. F., and Johannessen, T.: A decrease in the sink of atmospheric CO2 in the North Atlantic, Geophys. Res. Lett., 31, https://doi.org/10.1029/2003GL018957, 2004.
McQuatters-Gollop, A., Burkill, P. H., Beaugrand, G., Johns, D. G., Gattuso, J.-P., and Edwards, M.: Atlas of Calcifying Plankton: Results from the North Atlantic Continuous Plankton Recorder survey, Sir Alister Hardy Foundation for Ocean Science, Plymouth, UK, 20 pp., 2010.
Merico, A., Tyrrell, T., Brown, C. W., Groom, S. B., and Miller, P. I.: Analysis of satellite imagery for Emiliania huxleyi blooms in the Bering Sea before 1997, Geophys. Res. Lett., 30, https://doi.org/10.1029/2002GL016648, 2003.
Mokhov, I. I., and Smirnov, D. A.: El Niño–Southern Oscillation drives North Atlantic Oscillation as revealed with nonlinear techniques from climatic indices, Geophys. Res. Lett., 33, https://doi.org/10.1029/2005GL024557, 2006.
Najjar, R. G., Jin, X., Louanchi, F., Aumont, O., Caldeira, K., Doney, S. C., Dutay, J.-C., Follows, M., Gruber, N., Joos, F., Lindsay, K., Maier-Reimer, E., Matear, R., Matsumoto, K., Monfray, P., Mouchet, A., Orr, J. C., Plattner, G.-K., Sarmiento, J. L., Schlitzer, R., Slater, R. D., Weirig, M.-F., Yamanaka, Y., and Yool, A.: Impact of circulation on export production, dissolved organic matter, and dissolved oxygen in the ocen: Results from Phase II of the Ocean Carbon-cycle Model Intercomparison Project (OCMIP-2), Global Biogeochem. Cy., 21, https://doi.org/10.1029/2006GB002857, 2007.
NASA: Ocean colour biology group website, http://oceancolor.gsfc.nasa.gov/, 2010.
NOAA: Multivariate El Niño/Southern Oscillation, http://www.esrl.noaa.gov/psd/enso/mei, 2011.
Purdie, D. A. and Finch, M. S.: Impact of a coccolithorid bloom on dissolved carbon dioxide in sea water enclosures in a Norwegian fjord, Sarsia, 79, https://doi.org/10.1080/00364827.1994.10413569, 1994.
Raitsos, D. E., Lavender, S. J., Pradhan, Y., Tyrrell, T., Reid, P. C., and Edwards, M.: Coccolithophore bloom size variation in response to th regional environment of the subarctic North Atlantic, Liminol. Oceanogr., 51, 2122–2130, 2006.
Reid, P. C., Colebrook, J. M., Matthews, J. B. L., and Aiken, J.: The Continuous Plankton Recorder: concepts and history, from plankton indicator to undulating recorders, Prog. Oceanogr., 58, 117–173, 2003.
Ridgwell, A., Hargreaves, J. C., Edwards, N. R., Annan, J. D., Lenton, T. M., Marsh, R., Yool, A., and Watson, A.: Marine geochemical data assimilation in an efficient Earth System Model of global biogeochemical cycling, Biogeosciences, 4, 87–104, https://doi.org/10.5194/bg-4-87-2007, 2007.
Robertson, J. E., Robertson, C., Turner, D. R., Holligan, P., Watson, A. J., Boyd, P., Fernandez, E., and Finch, M.: The impact of a coccolithophore bloom on oceanic carbon uptake in the northeast Atlantic during summer 1991, Deep Sea Res. Pt. I, 41, 297–314, 1991.
Sabine, C. L., Feely, R. A., Gruber, N., Key, R. M., Lee, K., Bullister, J. L., Wanninkhof, R., Wong, C. S., Wallace, D. W. R., Tilbrook, B., Millero, F. J., Peng, T. H., Hozyr, A., Ono, T., and Rios, A. F.: The oceanic sink for anthropogenic CO2, Science, 305, 367–371, 2004.
Schuster, U. and Watson, A. J.: A variable and decreasing sink for atmospheric CO2 in the North Atlantic, J. Geophys. Res., 112, https://doi.org/10.1029/2006JC003941, 2007.
Shutler, J. D., Smyth, T. J., Land, P. E., and Groom, S. B.: A near-real time automatic MODIS data processing system, Int. J. Remote Sens., 25, 1049–1055, 2005.
Shutler, J. D., Grant, M. G., Miller, P. I., Rushton, E., and Anderson, K.: Coccolithophore bloom detection in the north east Atlantic using SeaWiFS: algorithm description, application and sensitivity analysis, Remote Sens. Environ., 114, 1008–1016, https://doi.org/10.1016/j.rse.2009.12.024, 2010.
Shutler, J. D., Smyth, T. J., Saux-Picart, S., Wakelin, S. L., Hyder, P., Orekhov, P., Grant, M. G., Tilstone, G. H., and Allen, J. I.: Evaluating the ability of a hydrodynamic ecosystem model to capture inter- and intra-annual spatial characteristics of chlorophyll-a in the north east Atlantic, J. Mar. Syst., 88, 169–182, https://doi.org/10.1016/j.jmarsys.2011.03.013, 2011.
Smyth, T. J., Tyrrell, T., and Tarrant, B.: Time series of coccolithophore activity in the Barents Sea from twenty years of satellite imagery, Geophys. Res. Lett., 31, https://doi.org/10.1029/2004GL019735, 2004.
Suykens, K., Delille, B., Chou, L., De Bodt, C., Harlay J., and Borges, A. V.: Dissolved inorganic carbon dynamics and air-sea carbon dioxide fluxes during coccolithophore blooms in the northwest European continental margin (northern Bay of Biscay), Global Biogeochem. Cy., 24, https://doi.org/10.1029/2009GB003730, 2010.
Takahashi, T., Sutherland, S. C., Wanninkhof, R., Sweeney, C., Feely, R. A., Chipman, D. W., Burke Hales, B., Friederich, G., Chavez, F., Watson, A. J., Bakker, D. C. E., Schuster, U., Metzl, N., Yoshikawa-Inoue, H., Ishii, M., Midorikawa, T., Sabine, C., Hoppema, J. M. J., Olafsson, J., Arnarson, T. S., Tilbrook, B., Johannessen, T., Olsen, A., Bellerby, R., Baar, H. J. W. d., Nojiri, Y., Wong, C. S., and Delille, B.: Climatological mean and decadal change in surface ocean pCO2 and net sea-air CO2 flux over the global oceans, Deep Sea Res. Pt. II, 56, 554–577, 2009.
Taylor, J. R.: An introduction to Error Analysis; the study of uncertainties in physical measurements, in, Second ed., edited by: McGuire, A., University Science Books, 1997.
Tyrrell, T., Holligan, P., and Mobley, C. D.: Optical impacts of oceanic coccolithophore blooms, J. Geophys. Res., 104, 3223–3241, 1999.
Tyrrell, T. and Merico, A.: Emiliania huxleyi: Bloom observations and the conditions that induce them, in: Coccolithophores: from Molecular processes to global impact, edited by: Thiertein, H. R., and Young, J. R., Springer-Verlag, 2004.
Wakelin, S., Holt, J. T., Blackford, J., Allen, J. I., Butenschon, M., and Artioli, Y.: Modeling the carbon fluxes of the Northwest European Continential Shelf: validation and budgets, J. Geophys. Res., https://doi.org/10.1029/2011JC007402, 2012.
Watson, A. J., Schuster, U., Bakker, D. C. E., Bates, N. R., Corbiere, A., Gonzalez-Davila, M., Friedrich, T., Hauck, J., Heinze, C., Johannessen, T., Kortzinger, A., Metzl, N., Olafsson, J., Olsen, A., Oschlies, A., Padin, X. A., Pfeil, B., Santana-Casiano, J. M., Steinhoff, T., Telszewski, M., Rios, A. F., Wallace, D. W. R., and Wanninkhof, R.: Tracking the Variable North Atlantic Sink for Atmospheric CO2, Science, 326, 1391–1393, 2009.
Yool, A., Popova, E. E., and Andersen, T. R.: Medusa-1.0:a new intermediate complexity plankton ecosystem model for the global domain, Geosci. Model Develop., 4, 381–417, https://doi.org/10.5194/gmd-4-381-2011, 2011.
Zeebe, R. E. and Wolf-Gladrow, D. A.: CO2 in seawater: equilibrium, kinetics, isotopes, Elsevier, Amsterdam, 346 pp., 2001.