Villefranche-sur-Mer, France
Villefranche-sur-Mer, France

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Zhang J.,University of Washington | Spitz Y.H.,Oregon State University | Steele M.,University of Washington | Ashjian C.,Woods Hole Oceanographic Institution | And 3 more authors.
Journal of Geophysical Research: Oceans | Year: 2010

We have developed a coupled 3-D pan-Arctic biology/sea ice/ocean model to investigate the impact of declining Arctic sea ice on the marine planktonic ecosystem over 1988-2007. The biophysical model results agree with satellite observations of a generally downward trend in summer sea ice extent during 1988-2007, resulting in an increase in the simulated photosynthetically active radiation (PAR) at the ocean surface and marine primary productivity (PP) in the upper 100 m over open water areas of the Arctic Ocean. The simulated Arctic sea ice thickness has decreased steadily during 1988-2007, leading to an increase in PAR and PP in sea ice-covered areas. The simulated total PAR in all areas of the Arctic Ocean has increased by 43%, from 146 TW in 1988 to 209 TW in 2007; the corresponding total PP has increased by 50%, from 456 Tg C yr-1 in 1988 to 682 Tg C yr-1 in 2007. The simulated PAR and PP increases mainly occur in the seasonally and permanently ice-covered Arctic Ocean. In addition to increasing PAR, the decline in sea ice tends to increase the nutrient availability in the euphotic zone by enhancing air-sea momentum transfer, leading to strengthened upwelling and mixing in the water column and therefore increased nutrient input into the upper ocean layers from below. The increasing nutrient availability also contributes to the increase in the simulated PP, even though significant surface nutrient drawdown in summer is simulated. In conjunction with increasing surface absorption of solar radiation and rising surface air temperature, the increasing surface water temperature in the Arctic Ocean peripheral seas further contributes to the increase in PP. As PP has increased, so has the simulated biomass of phytoplankton and zooplankton. Copyright 2010 by the American Geophysical Union.


Rottgers R.,Institute for Coastal Research | Doxaran D.,Laboratoire Doceanographie Of Villefranche | Dupouy C.,CNRS Mediterranean Institute of Oceanography (MIO) | Dupouy C.,CIRAD - Agricultural Research for Development
Optics Express | Year: 2016

The accurate determination of light absorption coefficients of particles in water, especially in very oligotrophic oceanic areas, is still a challenging task. Concentrating aquatic particles on a glass fiber filter and using the Quantitative Filter Technique (QFT) is a common practice. Its routine application is limited by the necessary use of high performance spectrophotometers, distinct problems induced by the strong scattering of the filters and artifacts induced by freezing and storing samples. Measurements of the sample inside a large integrating sphere reduce scattering effects and direct field measurements avoid artifacts due to sample preservation. A small, portable, Integrating Cavity Absorption Meter setup (QFT-ICAM) is presented, that allows rapid measurements of a sample filter. The measurement technique takes into account artifacts due to chlorophyll-a fluorescence. The QFT-ICAM is shown to be highly comparable to similar measurements in laboratory spectrophotometers, in terms of accuracy, precision, and path length amplification effects. No spectral artifacts were observed when compared to measurement of samples in suspension, whereas freezing and storing of sample filters induced small losses of water-soluble pigments (probably phycoerythrins). Remaining problems in determining the particulate absorption coefficient with the QFT-ICAM are strong sample-to-sample variations of the path length amplification, as well as fluorescence by pigments that is emitted in a different spectral region than that of chlorophyll-a. ©2015 Optical Society of America.


Siegel D.A.,University of California at Santa Barbara | Behrenfeld M.J.,Oregon State University | Maritorena S.,University of California at Santa Barbara | McClain C.R.,NASA | And 22 more authors.
Remote Sensing of Environment | Year: 2013

Photosynthetic production of organic matter by microscopic oceanic phytoplankton fuels ocean ecosystems and contributes roughly half of the Earth's net primary production. For 13. years, the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) mission provided the first consistent, synoptic observations of global ocean ecosystems. Changes in the surface chlorophyll concentration, the primary biological property retrieved from SeaWiFS, have traditionally been used as a metric for phytoplankton abundance and its distribution largely reflects patterns in vertical nutrient transport. On regional to global scales, chlorophyll concentrations covary with sea surface temperature (SST) because SST changes reflect light and nutrient conditions. However, the ocean may be too complex to be well characterized using a single index such as the chlorophyll concentration. A semi-analytical bio-optical algorithm is used to help interpret regional to global SeaWiFS chlorophyll observations from using three independent, well-validated ocean color data products; the chlorophyll a concentration, absorption by CDM and particulate backscattering. First, we show that observed long-term, global-scale trends in standard chlorophyll retrievals are likely compromised by coincident changes in CDM. Second, we partition the chlorophyll signal into a component due to phytoplankton biomass changes and a component caused by physiological adjustments in intracellular chlorophyll concentrations to changes in mixed layer light levels. We show that biomass changes dominate chlorophyll signals for the high latitude seas and where persistent vertical upwelling is known to occur, while physiological processes dominate chlorophyll variability over much of the tropical and subtropical oceans. The SeaWiFS data set demonstrates complexity in the interpretation of changes in regional to global phytoplankton distributions and illustrates limitations for the assessment of phytoplankton dynamics using chlorophyll retrievals alone. © 2013 Elsevier Inc.


Groundwater H.,WET Labs Inc. | Twardowski M.S.,WET Labs Inc. | Dierssen H.M.,University of Connecticut | Sciandra A.,Laboratoire Doceanographie Of Villefranche | Freeman S.A.,WET Labs Inc.
Journal of Atmospheric and Oceanic Technology | Year: 2012

Knowledge of particle size distributions (PSDs) in seawater is important for understanding several facets of marine science, such as the behavior of light scattering in seawater, phytoplankton dynamics, and biogeochemical cycling. Here, a method has been developed to quantify the size distribution of particle suspensions and characterize their chemical composition utilizing a scanning electron microscope (SEM) coupled with an energy dispersive spectrometer (EDS) and applying image analysis techniques, including automatic thresholding. The method was validated by verifying the PSD and chemical composition of the Arizona Test Dust (ATD), which has a well-documented size distribution and chemical composition. Size distributions of ATD particles containing specific elements important in the marine environment, such as silicon, iron, calcium, aluminum, and potassium, were quantified. PSDs determined with the technique in field samples from coastal Long Island Sound and the remote South Pacific were compared with other sizing methods, including electroresistivity and laser diffractometry. Most accurate results for PSD determinations occurred when the particle mass loading on the filter was between 0.04 and 0.1mg cm22. With this in mind, immediate feedback in the field can be provided to prepare appropriate filtration sample volumes due to a linear relationship between the beam attenuation coefficient at 650nm (c650) and the total suspended matter (TSM). Overall, the method presents two defining advantages in 1) minimizing user bias, because the majority of the analysis is automated, and 2) providing an elemental distribution in the context of a particle size distribution. © 2012 American Meteorological Society.


Christaki U.,University of Lille Nord de France | Van Wambeke F.,Aix - Marseille University | Lefevre D.,Aix - Marseille University | Lagaria A.,University of Lille Nord de France | And 16 more authors.
Biogeosciences | Year: 2011

The abundance and activity of the major members of the heterotrophic microbial community ĝ€" from viruses to ciliates ĝ€" were studied along a longitudinal transect across the Mediterranean Sea in the summer of 2008. The Mediterranean Sea is characterized by a west to-east gradient of deepening of DCM (deep chlorophyll maximum) and increasing oligotrophy reflected in gradients of biomass and production. However, within this well documented longitudinal trend, hydrological mesoscale features exist and likely influence microbial dynamics. Here we present data from a W-E transect of 17 stations during the period of summer stratification. Along the transect the production and fate of organic matter was investigated at three selected sites each one located in the centre of an anticyclonic eddy: in the Algero-Provencal Basin (St. A), the Ionian Basin (St. B), and the Levantine Basin (St. C). The 3 geographically distant eddies showed low values of the different heterotrophic compartments of the microbial food web, and except for viruses in site C, all integrated (0ĝ€"150 m) stocks were higher in reference stations located in the same basin outside the eddies. During our study the 3 eddies showed equilibrium between GPP (Gross Primary Production) and DCR (Dark Community Respiration). Integrated PPp (Particulate Primary Production) values at A, B and C varied from ∼140 to ∼190 mg C mĝ̂'2. © Author(s) 2011.


Gilerson A.,City University of New York | Ibrahim A.,City University of New York | Harmel T.,Laboratoire Doceanographie Of Villefranche | Tonizzo A.,City University of New York | Ahmed S.,City University of New York
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

The next generation of Ocean Color satellite sensors (PACE, NASA) will have polarization sensitive channels which will make possible to continue the time series of polarization acquisitions from space initiated by the French missions POLDER/PARASOL (CNES) and can be used to acquire additional information on ocean water constituents. The water attenuation coefficient is not retrievable by the exclusive use of the unpolarized measurements of the water-leaving radiance. However, we recently showed that the underwater degree of linear polarization (DoLP) can be fairly related to the attenuation/absorption ratio (c/a) which enables us to achieve retrievals of the absorption and attenuation coefficients from measurements of the Stokes components of the upwelling underwater light field. The relationship between the DoLP and the attenuation/absorption (c/a) ratio is investigated based on vector radiative transfer simulations of the underwater polarized light field for several wavelengths in the visible part of the spectrum, for a complete set of viewing geometries and for varying water compositions with water constituents include phytoplankton, non-algal particles and CDOM. It is shown that the relationship that exists between DoLP and c/a ratio has an excellent correlation for wide range of different viewing and Sun's geometries opening the possibility for air or space borne DoLP measurements of the ocean and therefore retrieval of additional water optical properties. © 2012 SPIE.


Ibrahim A.,City University of New York | Gilerson A.,City University of New York | Harmel T.,Laboratoire Doceanographie Of Villefranche | Tonizzo A.,City University of New York | And 2 more authors.
Optics Express | Year: 2012

The attenuation coefficient of the water body is not directly retrievable from measurements of unpolarized water-leaving radiance. Based on extensive radiative transfer simulations using the vector radiative transfer code RayXP, it is demonstrated that the underwater degree of linear polarization (DoLP) is closely related to the attenuation-to-absorption ratio (c/a) of the water body, a finding that enables retrieval of the attenuation coefficient from measurements of the Stokes components of the upwelling underwater polarized light field. The relationship between DoLP and the c/a ratio is investigated for the upwelling polarized light field for a complete set of viewing geometries, at several wavelengths in the visible part of the spectrum; for varying compositions of the aquatic environment, whose constituents include phytoplankton, non-algal particles, and color dissolved organic matter (CDOM); and for varying microphysical properties such as the refractive index and the slope of the Junge-type particle size distribution (PSD). Consequently, this study reveals the possibility for retrieval of additional inherent optical properties (IOPs) from air- or space-borne DoLP measurements of the water-leaving radiation. © 2012 Optical Society of America.


Frouin R.,University of California at San Diego | Loisel H.,Laboratoire dOceanologie et Geosciences | Poteau A.,Laboratoire Doceanographie Of Villefranche
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

The SIMBADA radiometer was designed to check the radiometric calibration of satellite ocean-color sensors and evaluate the atmospheric correction of ocean-color imagery. It measures marine reflectance and aerosol optical thickness in 11 spectral bands covering the spectral range 350 to 870 nm. Aerosol optical thickness is obtained by viewing the sun disk and marine reflectance by viewing the ocean surface through a vertical polarizer that minimizes sun glint and reflected skylight. The measurements made by SIMBADA during ACE-Asia (March-April 2001, Japan Sea) and AOPEX (July-August 2004, Mediterranean Sea) are compared with those made concomitantly by other ocean radiometers and sun photometers, i.e., MER, PRR, SPMR, Trios, TSRB, and BOUSSOLE instruments for marine reflectance and CIMEL and Microtops for aerosol optical thickness. Agreement is generally good between the various measurements or estimates. The SIMBADA aerosol optical thickness is within ±0.02 of the values obtained by other sun photometers. The SIMBADA marine reflectance, after correction for bi-directional effects (Q factor), does not exhibit biases when compared with estimates by other radiometers, which generally agree within ±10%. In some cases larger discrepancies exist, and they are largely explained by differences in solar irradiance. More accurate SIMBADA estimates may be obtained by improving the radiometric calibration, the correction for angular geometry and water body polarization, the calculation of incident solar irradiance, and the selection of data minimally affected by sky reflection. © 2010 SPIE.


Le Moullac G.,Center du Pacifique | Tiapari J.,Center du Pacifique | Teissier H.,Center du Pacifique | Martinez E.,Laboratoire Doceanographie Of Villefranche | Cochard J.-C.,French Research Institute for Exploitation of the Sea
Aquaculture International | Year: 2012

The growth and reproductive cycle of cultured black-lipped pearl oysters, Pinctada margaritifera (L.), were studied in the Gambier Islands (134°52′ W, 23°07′ S) from September 2002 to August 2003. Temperatures were recorded throughout the year, revealing seasonal temperature variations between 22.3 and 27.8°C. The mean annual chlorophyll a value, as computed from satellite data, was 0.188 ± 0.075 μg L -1. To study growth and reproduction, 720 two-year-old individuals were ear hung on long-lines suspended at a depth of 7 m. Samples were taken twice a month to obtain the following measurements: shell height; wet weight of flesh and total oyster; dry weight of adductor muscle, mantle and visceral mass; and glycogen content. Gonad development was also studied by histology on parallel samples. Growth was relatively fast during the first 6 months of the study: average shell height increased from 89.1 ± 9.1 to 119.7 ± 10.8 mm and total weight from 93.4 ± 24.5 to 155.1 ± 33.6 g, between September and the end of March. Subsequently, from April to August, no significant growth was observed for shell and flesh, while the muscle weight decreased significantly. Condition index (CI), defined as the ratio of wet weight of the visceral mass to shell weight, and histological changes in the gonad revealed 3 significant reproductive events of different intensities. The analysis of correlations revealed a specific effect of the chlorophyll a concentration on the growth of shell and soma, and one of the temperature on tissue glycogen content. This study also showed also that CI could be an efficient indicator of reproductive events in pearl oyster. It thus appears that the development of gonads goes on throughout the year in the Gambier Islands, without any detectable phase of sexual rest. © 2011 Springer Science+Business Media B.V.


Charantonis A.A.,Center Detudes Et Of Recherche En Informatique | Charantonis A.A.,Laboratory dOceanographie Climat Experimentations Approches Numeriques | Testor P.,Laboratory dOceanographie Climat Experimentations Approches Numeriques | Mortier L.,ENSTA ParisTech | And 2 more authors.
Procedia Computer Science | Year: 2015

We present a novel approach named ITCOMP SOM that uses iterative self-organizing maps (SOM) to progressively reconstruct missing data in a highly correlated multidimensional dataset. This method was applied for the completion of a complex oceanographic data-set containing glider data from the EYE of the Levantine experiment of the EGO project. ITCOMP SOM provided reconstructed temperature and salinity profiles that are consistent with the physics of the phenomenon they sampled. A cross-validation test was performed and validated the approach, providing a root mean square error of providing a root mean square error of 0,042°C for the reconstruction of the temperature profiles and 0,008 PSU for the simultaneous reconstruction of the salinity profiles. © The Authors. Published by Elsevier B.V.

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