Contribution des données isotopiques de deutérium, oxygène-18, hélium-3 et tritium, à l'étude de la circulation de la Mer Rouge

Les données concernant les différents traceurs isotopiques D, 18O, 3He et tritium sont relatives à la campagne Merou de juillet 1982. Les isotopes stables D et 18O, associés aux données de salinité, mettant en évidence une structure à trois couches des eaux au niveau du seuil de Bab-el-Mandeb, au moins jusqu'à 15°N. Une approche du rapport évaporation-précipitation E/P est tentée. Les données d'hélium-3 constituent des contraintes importantes au plan de la circulation profonde et intermédiaires. Une source hydrothermale active a été échantillonnée vers 21°N, responsable de l'enrichissement en hélium-3 est sans doute l'effet d'un courant de retour centré vers 600-800 m. L'ensemble des données isotopiques indique que le flux sortant vers l'Océan Indien provient principalement d'eaux de subsurface s'écoulant du Nord à une profondeur voisine de celle du seuil de Bab-el-Mandeb. Pendant cette situation d'été, la composante des eaux profondes dans le flux sortant est inférieure à 10 %. (Résumé d'auteur

Tritium in the western Mediterranean Sea during 1981 Phycemed cruise

International audienceWe report on simultaneous hydrological and tritium data taken in the western Mediterranean Sea during April 1981 and which implement our knowledge of the spatial and temporal variability of the convection process occurring in the Northern Basin (Gulf of Lion, Ligurian Sea). The renewal time of the deep waters in the Medoc area is calculated to be 11 ± 2 years using a box-model assymption. An important local phenomenon of “cascading” off the Ebro River near the Spanish coast is, noticeable by the use of tritium data. In the Sardinia Straits area tritium data indicate very active mixing between 100 and 500 m depth. The tritium subsurface maxima in Sardinia Straits suggests the influence of not only the Levantine Intermediate Water (LIW) but also an important shallower component. In waters deeper than 500m, an active mixing occurs between the deep water and the LIW via an intermediate water mass from the Tyrrhenian Sea by “salt-fingering”. Assuming a two end-member mixing. We determine the deep tritium content in the Sardinia Channel to be 1.8 TU. For comparison, the deep tritium content of the Northern Basin is equal to 1.3 TU.Tritium data relative to the Alboran Sea show that a layer of high tritium content persists all along its path from Sardifia to Gibraltar on a density surface shallower than the intermediate water. The homogeneity of the deep tritium concentrations between 1200 m depth and the bottom corroborate the upward “pumping” and westward circulation of deep waters along the continental slope of the North African Shelf. From the data measured in the Sardinia Straits and in the Alboran Sea, and upper limit of the deep advection rate of the order of 0.5 cm s$^{−1}$ is estimated

Annual to interannual variations of ƒCO2 in the northwestern Mediterranean Sea: Results from hourly measurements made by CARIOCA buoys, 1995–1997

A time series of fCO2, SST, and fluorescence data was collected between 1995 and 1997 by a CARIOCA buoy moored at the DyFAMed station (Dynamique des Flux Atmospheriques en Mediterranée) located in the northwestern Mediterranean Sea. On seasonal timescales, the spring phytoplankton bloom decreases the surface water fCO2 to approximately 290 µatm, followed by summer heating and a strong increase in fCO2 to a maximum of approximately 510 µatm. While the ΔfCO2 shows strong variations on seasonal timescales, the annual average air-sea disequilibrium is only 2 µatm. Temperature-normalized fCO2 shows a continued decrease in dissolved CO2 throughout the summer and fall at a rate of approximately 0.6 µatm d-1. The calculated annual air-sea CO2 transfer rate is -0.10 to -0.15 moles CO2 m-2 y-1, with these low values reflecting the relatively weak wind speed regime and small annual air-sea fCO2 disequilibrium. Extrapolating this rate over the whole Mediterranean Sea would lead to a flux of approximately -3 × 1012 to -4.5 × 1012 grams C y-1, in good agreement with other estimates. An analysis of the effects of sampling frequency on annual air-sea CO2 flux estimates showed that monthly sampling is adequate to resolve the annual CO2 flux to within approximately ±10 - 18% at this site. Annual flux estimates made using temperature-derived fCO2 based on the measured fCO2-SST correlations are in agreement with measurement-based calculations to within ± 7-10% (depending on the gas transfer parameterization used), and suggest that annual CO2 flux estimates may be reasonably well predicted in this region from satellite or model-derived SST and wind speed information

The distribution of helium 3 in the deep Western and Southern Indian Ocean

Almost a decade after the Geochemical Ocean Sections Study Indian Expedition, the new deep 3He data from the INDIGO program give a further insight into the distribution of this tracer in the Indian Ocean. This distribution exhibits some major features related on one hand to a hydrothermal 3He input in the Gulf of Aden and on the Mid-Indian Ocean Ridge, and on the other to the origin of the water masses and to the characteristics of the deep circulation. (D'après résumé d'auteur

Increase of dissolved inorganic carbon and decrease in pH in near-surface waters in the Mediterranean Sea during the past two decades

Two 3-year time series of hourly measurements of the fugacity of CO2 (fCO2) in the upper 10 m of the surface layer of the northwestern Mediterranean Sea have been recorded by CARIOCA sensors almost two decades apart, in 1995–1997 and 2013–2015. By combining them with the alkalinity derived from measured temperature and salinity, we calculate changes in pH and dissolved inorganic carbon (DIC). DIC increased in surface seawater by ∼25 µmol kg−1 and fCO2 by 40 µatm, whereas seawater pH decreased by ∼0.04 (0.0022 yr−1). The DIC increase is about 15 % larger than expected from the equilibrium with atmospheric CO2. This could result from natural variability, e.g. the increase between the two periods in the frequency and intensity of winter convection events. Likewise, it could be the signature of the contribution of the Atlantic Ocean as a source of anthropogenic carbon to the Mediterranean Sea through the Strait of Gibraltar. We then estimate that the part of DIC accumulated over the last 18 years represents ∼30 % of the total inventory of anthropogenic carbon in the Mediterranean Sea

Sensors and Systems for in situ Observations of Marine Carbon Dioxide System Variables

Autonomous chemical sensors are required to document the marine carbon dioxide system's evolving response to anthropogenic CO2 inputs, as well as impacts on short- and long-term carbon cycling. Observations will be required over a wide range of spatial and temporal scales, and measurements will likely need to be maintained for decades. Measurable CO2 system variables currently include total dissolved inorganic carbon (DIC), total alkalinity (AT), CO2 fugacity (fCO2), and pH, with comprehensive characterization requiring measurement of at least two variables. These four parameters are amenable to in situ analysis, but sustained deployment remains a challenge. Available methods encompass a broad range of analytical techniques, including potentiometry, spectrophotometry, conductimetry, and mass spectrometry. Instrument capabilities (precision, accuracy, endurance, reliability, etc.) are diverse and will evolve substantially over the time that the marine CO2 system undergoes dramatic changes. Different suites of measurements/parameters will be appropriate for different sampling platforms and measurement objectives

A multi-decade record of high quality fCO2 data in version 3 of the Surface Ocean CO2 Atlas (SOCAT)

The Surface Ocean CO2 Atlas (SOCAT) is a synthesis of quality-controlled fCO2 (fugacity of carbon dioxide) values for the global surface oceans and coastal seas with regular updates. Version 3 of SOCAT has 14.7 million fCO2 values from 3646 data sets covering the years 1957 to 2014. This latest version has an additional 4.6 million fCO2 values relative to version 2 and extends the record from 2011 to 2014. Version 3 also significantly increases the data availability for 2005 to 2013. SOCAT has an average of approximately 1.2 million surface water fCO2 values per year for the years 2006 to 2012. Quality and documentation of the data has improved. A new feature is the data set quality control (QC) flag of E for data from alternative sensors and platforms. The accuracy of surface water fCO2 has been defined for all data set QC flags. Automated range checking has been carried out for all data sets during their upload into SOCAT. The upgrade of the interactive Data Set Viewer (previously known as the Cruise Data Viewer) allows better interrogation of the SOCAT data collection and rapid creation of high-quality figures for scientific presentations. Automated data upload has been launched for version 4 and will enable more frequent SOCAT releases in the future. High-profile scientific applications of SOCAT include quantification of the ocean sink for atmospheric carbon dioxide and its long-term variation, detection of ocean acidification, as well as evaluation of coupled-climate and ocean-only biogeochemical models. Users of SOCAT data products are urged to acknowledge the contribution of data providers, as stated in the SOCAT Fair Data Use Statement. This ESSD (Earth System Science Data) “living data” publication documents the methods and data sets used for the assembly of this new version of the SOCAT data collection and compares these with those used for earlier versions of the data collection (Pfeil et al., 2013; Sabine et al., 2013; Bakker et al., 2014). Individual data set files, included in the synthesis product, can be downloaded here: doi:10.1594/PANGAEA.849770. The gridded products are available here: doi:10.3334/CDIAC/OTG.SOCAT_V3_GRID

Rain-induced turbulence and air-sea gas transfer

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 114 (2009): C07009, doi:10.1029/2008JC005008.Results from a rain and gas exchange experiment (Bio2 RainX III) at the Biosphere 2 Center demonstrate that turbulence controls the enhancement of the air-sea gas transfer rate (or velocity) k during rainfall, even though profiles of the turbulent dissipation rate ɛ are strongly influenced by near-surface stratification. The gas transfer rate scales with ɛ inline equation for a range of rain rates with broad drop size distributions. The hydrodynamic measurements elucidate the mechanisms responsible for the rain-enhanced k results using SF6 tracer evasion and active controlled flux technique. High-resolution k and turbulence results highlight the causal relationship between rainfall, turbulence, stratification, and air-sea gas exchange. Profiles of ɛ beneath the air-sea interface during rainfall, measured for the first time during a gas exchange experiment, yielded discrete values as high as 10−2 W kg−1. Stratification modifies and traps the turbulence near the surface, affecting the enhancement of the transfer velocity and also diminishing the vertical mixing of mass transported to the air-water interface. Although the kinetic energy flux is an integral measure of the turbulent input to the system during rain events, ɛ is the most robust response to all the modifications and transformations to the turbulent state that follows. The Craig-Banner turbulence model, modified for rain instead of breaking wave turbulence, successfully predicts the near-surface dissipation profile at the onset of the rain event before stratification plays a dominant role. This result is important for predictive modeling of k as it allows inferring the surface value of ɛ fundamental to gas transfer.This work was funded by a generous grant from the David and Lucile Packard Foundation and the Lamont-Doherty Earth Observatory Climate Center. Additional funding was provided by the National Science Foundation (OCE-05-26677) and the Office of Naval Research Young Investigator Program (N00014-04-1-0621)

An update to the Surface Ocean CO₂ Atlas (SOCAT version 2)

The Surface Ocean CO₂ Atlas (SOCAT), an activity of the international marine carbon research community, provides access to synthesis and gridded fCO₂ (fugacity of carbon dioxide) products for the surface oceans. Version 2 of SOCAT is an update of the previous release (version 1) with more data (increased from 6.3 million to 10.1 million surface water fCO₂ values) and extended data coverage (from 1968–2007 to 1968–2011). The quality control criteria, while identical in both versions, have been applied more strictly in version 2 than in version 1. The SOCAT website (http://www.socat.info/) has links to quality control comments, metadata, individual data set files, and synthesis and gridded data products. Interactive online tools allow visitors to explore the richness of the data. Applications of SOCAT include process studies, quantification of the ocean carbon sink and its spatial, seasonal, year-to-year and longerterm variation, as well as initialisation or validation of ocean carbon models and coupled climate-carbon models