Abstract:The accurate measurement of suspended particulate matter (SPM) concentrations in coastal waters is of crucial importance for ecosystem studies, sediment transport monitoring, and assessment of anthropogenic impacts in the coastal ocean. Ocean color remote sensing is an efficient tool to monitor SPM spatio-temporal variability in coastal waters. However, near-shore satellite images are complex to correct for atmospheric effects due to the proximity of land and to the high level of reflectance caused by high SPM concentrations in the visible and near-infrared spectral regions. The water reflectance signal (ρ w ) tends to saturate at short visible wavelengths when the SPM concentration increases. Using a comprehensive dataset of high-resolution satellite imagery and in situ SPM and water reflectance data, this study presents (i) an assessment of existing atmospheric correction (AC) algorithms developed for turbid coastal waters; and (ii) a switching method that automatically selects the most sensitive SPM vs. ρ w relationship, to avoid saturation effects when computing the SPM concentration. The approach is applied to satellite data acquired by three medium-high spatial resolution sensors (Landsat-8/Operational Land Imager, National Polar-Orbiting Partnership/Visible Infrared Imaging Radiometer Suite and Aqua/Moderate Resolution Imaging Spectrometer) to map the SPM concentration in some of the most turbid areas of the European coastal ocean, namely the Gironde and Loire estuaries as well as Bourgneuf Bay on the French Atlantic coast. For all three sensors, AC methods based on the use of short-wave infrared (SWIR) spectral bands were tested, and the consistency of the retrieved water reflectance was examined along transects from low-to high-turbidity waters. For OLI data, we also compared a SWIR-based AC (ACOLITE) with a method based on multi-temporal analyses of atmospheric constituents (MACCS). For the selected scenes, the ACOLITE-MACCS difference was lower than 7%. Despite some inaccuracies in ρ w retrieval, we demonstrate that the SPM concentration can be reliably estimated using OLI, MODIS and VIIRS, regardless of their differences in spatial and spectral resolutions. Match-ups between the OLI-derived SPM concentration and autonomous field measurements from the Loire and Gironde estuaries' monitoring networks provided satisfactory results. The multi-sensor approach together with the multi-conditional algorithm presented here can be applied to the latest generation of ocean color

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At the end of the SPOT4 mission, a four-month experiment was conducted in 2013 to acquire high spatial (20 m) and high temporal (5 days) resolution satellite data. In addition to the SPOT4 (Take5) dataset, we used several Landsat5, 7, 8 images to document the variations in suspended particulate matter (SPM) concentration in the turbid Gironde and Loire estuaries (France). Satellite-derived SPM concentration was validated using automated in situ turbidity measurements from two monitoring networks. The combination of a multi-temporal atmospheric correction method with a near-infrared to visible ), at an accuracy sufficient to detect the maximum turbidity zone (MTZ) in both estuaries. Such a multi-sensor approach can be applied to high spatial resolution satellite archives and to the new ESA Sentinel-2 mission. It offers a promising framework to study the response of estuarine ecosystems to global changes at unprecedented spatio-temporal resolution.

In order to provide information on the production and the distribution of hydrothermal particulate and biological material produced by deep-sea hydrothermal vents, three moorings with sediment traps and currentmeters were deployed for one year in the Azores Triple Junction region. Two moorings were positioned close to two hydrothermal vent fields at the Mid-Atlantic Ridge (Rainbow, 36°14′N, 33°54′W, 2250 m depth and Lucky Strike 37°17′N, 32°17′W, 1600 m depth). A third was moored out of the influence of the Rainbow vents representing the reference of the pelagic flux in this area. At the Rainbow field, particulate flux (range 341-634 g m−2 d−1) showed a high temporal variation controlled essentially by the current direction. The particles were characterized by a high concentration of total sulfur (16.4%) and copper (8.6%) and a low concentration of organic carbon (1.4%). Bivalves collected in the trap belonged to the hydrothermal mytilid Bathymodiolus azoricus and were all in the prejuvenile prodissoconch II stage of their development. Their density decreased strongly between July and September, indicating a possible discontinuous reproduction of this species. The particles at Lucky Strike were rich in barium and the calculated flux was lower than at Rainbow (range 52-308 g m−2 d−1) because of the translucent fluid poor in particles emitted at this shallower station. However, a peak in the flux was observed in May corresponding to the seasonal phytoplankton bloom. Two different bivalve species were sampled in this trap. The most abundant was B. azoricus. However, their development stages showed higher variations compared to the Rainbow trap. The abundance of mussels in the trap was very low throughout the year and does not allow one to show significant spawning periodicity.

Abstract. Measurements of carbon dioxide fluxes were performed over a temperate intertidal mudflat in southwestern France using the micrometeorological Eddy Covariance (EC) technique. EC measurements were carried out in two contrasting sites of the Arcachon flat during four periods and in three different seasons (autumn 2007, summer 2008, autumn 2008 and spring 2009). In addition, satellite images of the tidal flat at low tide were used to link the net ecosystem CO 2 exchange (NEE) with the occupation of the mudflat by primary producers, particularly by Zostera noltii meadows. CO 2 fluxes during the four deployments showed important spatial and temporal variations, with the flat rapidly shifting from sink to source with the tide. Absolute CO 2 fluxes showed generally small negative (influx) and positive (efflux) values, with larger values up to −13 µmol m −2 s −1 for influxes and 19 µmol m −2 s −1 for effluxes. Low tide during the day was mostly associated with a net uptake of atmospheric CO 2 . In contrast, during immersion and during low tide at night, CO 2 fluxes where positive, negative or close to zero, depending on the season and the site. During the autumn of 2007, at the innermost station with a patchy Zostera noltii bed (cover of 22 ± 14 % in the wind direction of measurements), CO 2 influx was −1.7 ± 1.7 µmol m −2 s −1 at low tide during the day, and the efflux was 2.7 ± 3.7 µmol m −2 s −1 at low tide during the night. A gross primary production (GPP) of 4.4 ± 4.1 µmol m −2 s −1 during emersion could be attributed to microphytobenthic communities. During the summer and autumn of 2008, at the central station with a dense eelgrass bed (92 ± 10 %), CO 2 uptakes at low tide during the day were −1.5 ± 1.2 and −0.9 ± 1.7 µmol m −2 s −1 , respectively. Night time effluxes of CO 2 were 1.0 ± 0.9 and 0.2 ± 1.1 µmol m −2 s −1 in summer and autumn, respectively, resulting in a GPP during emersion of 2.5 ± 1.5 and 1.1 ± 2.0 µmol m −2 s −1 , respectively, attributed primarily to the seagrass community. At the same station in April 2009, before Zostera noltii started to grow, the CO 2 uptake at low tide during the day was the highest (-2.7 ± 2.0 µmol m −2 s −1 ). Influxes of CO 2 were also observed during immersion at the central station in spring and early autumn and were apparently related to phytoplankton blooms occurring at the mouth of the flat, followed by the advection of CO 2 -depleted water with the flooding tide.Published by Copernicus Publications on behalf of the European Geosciences Union. P. Polsenaere et al.: Spatial and temporal CO 2 exchanges measured by Eddy CovarianceAlthough winter data as well as water carbon measurements would be necessary to determine a precise CO 2 budget for the flat, our results suggest that tidal flat ecosystems are a modest contributor to the CO 2 budget of the coastal ocean.

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