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Toulouse, France

Zhang J.,East China Normal University | Gilbert D.,Maurice Lamontagne Institute | Gooday A.J.,UK National Oceanography Center | Levin L.,University of California at San Diego | And 17 more authors.
Biogeosciences | Year: 2010

Hypoxia has become a world-wide phenomenon in the global coastal ocean and causes a deterioration of the structure and function of ecosystems. Based on the collective contributions of members of SCOR Working Group #128, the present study provides an overview of the major aspects of coastal hypoxia in different biogeochemical provinces, including estuaries, coastal waters, upwelling areas, fjords and semi-enclosed basins, with various external forcings, ecosystem responses, feedbacks and potential impact on the sustainability of the fishery and economics. The obvious external forcings include freshwater runoff and other factors contributing to stratification, organic matter and nutrient loadings, as well as exchange between coastal and open ocean water masses. Their different interactions set up mechanisms that drive the system towards hypoxia. Coastal systems also vary in their relative susceptibility to hypoxia depending on their physical and geographic settings. It is understood that coastal hypoxia has a profound impact on the sustainability of ecosystems, which can be seen, for example, by the change in the food-web structure and system function; other influences include compression and loss of habitat, as well as changes in organism life cycles and reproduction. In most cases, the ecosystem responds to the low dissolved oxygen in non-linear ways with pronounced feedbacks to other compartments of the Earth System, including those that affect human society. Our knowledge and previous experiences illustrate that there is a need to develop new observational tools and models to support integrated research of biogeochemical dynamics and ecosystem behavior that will improve confidence in remediation management strategies for coastal hypoxia. © Author(s) 2010. CC Attribution 3.0 License. Source


Dupouy C.,IRD Montpellier | Savranski T.,IRD Montpellier | Lefevre J.,IRD Montpellier | Despinoy M.,center | And 8 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

We present data collected as part of VALidation HYperspectral of a BIOgeochemical model (ValHyBio), a PNTSsponsored program dedicated to chlorophyll satellite imaging and validation as affected by bathymetry in the South Western Tropical Lagoon of New Caledonia. The specific goals of ValHyBio are to: - examine time-dependent oceanic reflectance in relation to dynamic surface processes, - construct field/satellite reflectance-based chlorophyll models, - investigate the feasibility of inverting the model to yield surface chlorophyll and turbidity, and - validate the biogeochemical model with field/satellite observations. The in situ bio-optical parameters include absorption coefficients by CDOM and particles, Secchi disk depth, backscattering coefficient, pigment concentration, suspended matter concentration, and K-dPAR. They are measured every month at 5 stations, of contrasted bathymetry and bottom reflectance, as well as at a reference station situated 4 miles offshore, and at a station over coral reefs. Remote sensing reflectance is calculated from the absorption and backscattering coefficients and compared with satellite data. SeaWIFS and MODIS Aqua match-ups collected over the period 1997-2010 (ValHySat database) are used. Satellite retrievals are examined as a function of bathymetry and for the special case of Trichodesmium red tides. The feasibility of a long-term monitoring program of water optical properties with satellite remote sensing techniques is examined in the frame of the GOPS (South Pacific Integrated Observatory). © 2010 SPIE. Source


Dupouy C.,IRD Montpellier | Savranski T.,IRD Montpellier | Lefevre J.,IRD Montpellier | Despinoy M.,Center of Noumea | And 7 more authors.
34th International Symposium on Remote Sensing of Environment - The GEOSS Era: Towards Operational Environmental Monitoring | Year: 2011

We present data collected as part of VALidation HYperspectral of a BIOgeochemical model (ValHyBio), a PNTS-sponsored program dedicated to chlorophyll satellite imaging and validation as affected by bathymetry in the South Western Tropical Lagoon of New Caledonia. MODIS Aqua match-ups collected over the period 1997-2010 (ValHySat database) are examined for two algorithms OC3 and OC5. Source


Vazquez-Cuervo J.,Jet Propulsion Laboratory | Dewitte B.,LEGOS IRD | Chin T.M.,Jet Propulsion Laboratory | Armstrong E.M.,Jet Propulsion Laboratory | Alburqueque E.,National Major San Marcos University
Remote Sensing of Environment | Year: 2013

The Peruvian Coastal Upwelling System (PCUS) is one of the most productive fisheries in the world. Upwelling events are associated with changes in the magnitude and location of frontal structures. SST gradients from four different data sets, NCDC, REMSS, OSTIA, and MUR are compared in two test areas off the PCUS: Païta (5°S) and Pisco (14°S). In both areas gradients derived from the MUR data set show greater magnitudes, as well as larger seasonal cycles. Off Pisco, the magnitude of the seasonal cycle of 2.2. °C/100. km in MUR is larger than the one derived from the lower resolution data sets. All data sets at Pisco exhibit a seasonal cycle that peaks in late Austral summer and early fall. Hovmöller diagrams calculated at 5.5°S, 10.5°S, and 14.5°S show clearly defined offshore maxima in the cross-shore gradients for all the data sets. Upwelling scales determined by the distance to the first maxima vary depending on the data set used. At 5.5°S upwelling scales vary from 10. km for MUR to 50. km for NCDC. At 14.5°S the scales vary from 20. km for MUR to 40. km for OSTIA. All four data sets show similar large-scale structures associated with the Peruvian upwelling. However, MUR shows finer scale structures that are most likely due to submesoscale to mesoscale eddies. Sub-sampled MUR 1. km data at the 25. km, 9. km, and 4. km resolutions compare well in magnitude and phase with the lower resolution products. Agreement in gradient magnitude between the lower resolution data sets and the MUR sub-sampled at their respective resolutions implies that the pixel-to-pixel analysis noise in MUR is at a similar level as the other data sets. © 2012. Source


Monteiro P.M.S.,South African Council for Scientific and Industrial Research | Monteiro P.M.S.,University of Cape Town | Dewitte B.,LEGOS IRD | Dewitte B.,Instituto Del Mar Del Peru Imarpe | And 4 more authors.
Environmental Research Letters | Year: 2011

In this study we investigate the possible reasons for the widespread differences between the seasonal cycles of carbon production and export compared to those of hypoxia in eastern boundary upwelling systems. An idealized model is proposed that qualitatively characterizes the relative roles of physics and biogeochemical fluxes. The model is tested on three contrasting upwelling systems: the Benguela (from relatively aerated to interannual anoxic), the Humboldt (sub-oxic and interannually anoxic) and the Cariaco (permanently anoxic). Overall we propose that shelf hypoxia variability can be explained on the basis of the interaction between ventilation by ocean boundary forcing through ocean-shelf exchange and the role of shelf geometry in the retention of shelf-based particulate organic carbon (POC) fluxes. We aim to identify the hypoxia regimes associated with low ventilation - wide-shelf systems and high ventilation - narrow-shelf systems, considering them as extremes of conditions controlled by the two factors. We propose that this may help to explain differences in the seasonal cycles of the biogeochemical drivers and responses as well as difference between upwelling systems and within individual upwelling systems. It is suggested that when seasonal hypoxia emerges it does so preferentially at a wide-shelf part of a system. © 2011 IOP Publishing Ltd. Source

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