Distribution of normalized water-leaving radiances at UV and visible wave bands in relation with chlorophyll a and colored detrital matter content in the southeast Pacific

International audience[1] In-water radiometric measurements were performed in the southeast Pacific (8°S-35°S, 141°W-72°W) from October to December 2004 during the Biogeochemistry and Optics South Pacific Experiment cruise. Normalized water-leaving radiances (nL w (l)) were determined at eight wave bands within the ultraviolet (UV) (305, 325, 340, and 380 nm) and visible (412, 443, 490, and 565 nm) spectral domains. The highest nL w (l) (mW cm À2 sr À1) were recorded in the hyperoligotrophic waters of the South Pacific Gyre, with values increasing with wavelength from 305 (nL w = 0.64) to 380 nm (nL w = 3.18) in the UV range and decreasing from 412 (nL w = 4.46) to 565 nm (nL w = 0.23) in the visible region. The intense nL w (l) observed in the violet-blue domains were attributed to very low absorptions of colored detrital matter (CDM), likely related to a strong photobleaching of colored dissolved organic matter in the surface waters. We evaluated the relationships between the UV, violet, or blue/green wave band ratios of nL w (l) and surface total chlorophyll a (TChl a) concentration and CDM absorption (a CDM (l)). For TChl a, the best correlation was found with the blue/green ratio at 443 nm: TChl a (mg m À3) = 2.37[nL w (443)/nL w (565)] À1.51 (r 2 = 0.86 and RMS error (RMSE) = 23%). By contrast, for a CDM (l), the best correlation was observed when using the UV/green ratio at 325 nm: a CDM (325) (m À1) = 0.16[nL w (325)/nL w (565)] À0.69 (r 2 = 0.82 and RMSE = 16%). These results show the potential role of nL w (l) at UV wave bands for the assessment, through empirical algorithms, of colored detrital matter in the surface oceanic waters. Citation: Tedetti, M., B. Charrière, A. Bricaud, J. Para, P. Raimbault, and R. Sempéré (2010), Distribution of normalized water-leaving radiances at UV and visible wave bands in relation with chlorophyll a and colored detrital matter content in the southeast Pacific

Fluorescence properties of dissolved organic matter in coastal Mediterranean waters influenced by a municipal sewage effluent (Bay of Marseilles, France)

International audienceFluorescent dissolved organic matter (FDOM) in coastal marine waters influenced by the municipal sewage effluent (SE) from Marseilles City (France, north-western Mediterranean Sea) has been characterised. Samples were collected eleven times from September 2008 to June 2010 in the Bay of Marseilles along a coast-open sea transect from the SE outlet in the South Bay and at the Mediterranean Institute Observation site in the central Bay. Fluorescence excitation-emission matrices combined with parallel factor analysis (PARAFAC) allowed the identification of two protein-like (tyrosine C1, with excitation maxima (lEx) and an emission maximum (lEm) of ,230, 275/306 nm; tryptophan C2, lEx/lEm,230, 270/346 nm) and three humic-like components (marine humic C3, lEx/lEm 280/386 nm; C4, lEx/lEm 235, 340/410 nm; C5, lEx/lEm 255, 365/474 nm). From the SE outlet to the central Bay, a gradient appeared, with decreasingFDOM intensities, decreasing dissolved organic carbon, particulate carbon, nutrients and faecal bacteria concentrations and increasing salinity values. This gradient was associated with decreasing abundances in protein-like fluorophores and rising abundances in humic-like (C3 and C5) materials. This shift in FDOM composition illustrated the decrease in wastewater inputs and the increase in marine sources of DOM along the transect. FDOM data showed that the Marseilles SE spread up to 1500m off the outlet, but it did not reach the central Bay. Tryptophan-like material was the dominant fluorophore in the SE and displayed the highest correlations with biogeochemical parameters (organic carbon, phosphates, faecal bacteria). Therefore, it is proposed to use its fluorescence intensity to detect and track SE inputs in the Marseilles coastal marine waters

Fluorescence and absorption properties of chromophoric dissolved organic matter (CDOM) in coastal surface waters of the northwestern Mediterranean Sea, influence of the Rhône River

International audienceSeawater samples were collected monthly in surface waters (2 and 5 m depths) of the Bay of Marseilles (northwestern Mediterranean Sea; 5 • 17 30 E, 43 • 14 30 N) during one year from November 2007 to December 2008 and studied for total organic carbon (TOC) as well as chro-mophoric dissolved organic matter (CDOM) optical properties (absorbance and fluorescence). The annual mean value of surface CDOM absorption coefficient at 350 nm [a CDOM (350)] was very low (0.10 ± 0.02 m −1) in comparison to values usually found in coastal waters, and no significant seasonal trend in a CDOM (350) could be determined. By contrast, the spectral slope of CDOM absorption (S CDOM) was significantly higher (0.023 ± 0.003 nm −1) in summer than in fall and winter periods (0.017 ± 0.002 nm −1), reflecting either CDOM photobleaching or production in surface waters during stratified sunny periods. The CDOM fluorescence, assessed through excitation emission matrices (EEMs), was dominated by protein-like component (peak T; 1.30-21.94 QSU) and marine humic-like component (peak M; 0.55-5.82 QSU), while terrestrial humic-like fluores-cence (peak C; 0.34-2.99 QSU) remained very low. This reflected a dominance of relatively fresh material from biological origin within the CDOM fluorescent pool. At the end of summer, surface CDOM fluorescence was very low and strongly blue shifted, reinforcing the hypothesis of CDOM photobleaching. Our results suggested that unusual Rhône Correspondence to: R. Sempéré ([email protected]) River plume eastward intrusion events might reach Mar-seilles Bay within 2-3 days and induce local phytoplank-ton blooms and subsequent fluorescent CDOM production (peaks M and T) without adding terrestrial fluorescence signatures (peaks C and A). Besides Rhône River plumes, mixing events of the entire water column injected relative aged (peaks C and M) CDOM from the bottom into the surface and thus appeared also as an important source of CDOM in surface waters of the Marseilles Bay. Therefore, the assessment of CDOM optical properties, within the hydrological context, pointed out several biotic (in situ biological production , biological production within Rhône River plumes) and abiotic (photobleaching, mixing) factors controlling CDOM transport, production and removal in this highly urbanized coastal area

Effect of Acidic Industrial Effluent Release on Microbial Diversity and Trace Metal Dynamics During Resuspension of Coastal Sediment

Both industrial effluent discharge and the resuspension of contaminated marine sediments are important sources of trace metals in seawater which potentially affect marine ecosystems. The aim of this study was to evaluate the impact of the industrial wastewaters having acidic pH (2–3) and containing trace metals on microbial diversity in the coastal ecosystem of the Gulf of Gabès (Tunisia, southern Mediterranean Sea) subjected to resuspension events of marine sediments. Four trace elements (As, Cd, U, and V) were monitored during 10-day sediment resuspension experiments. The highest enrichment in the seawater dissolved phase was observed for Cd followed by U, V, and As. Cd remobilization was improved by indigenous microbial community, while U release was mainly abiotic. Acidic effluent addition impacted both trace metal distribution and microbial diversity, particularly that of the abundant phylum Bacteroidetes. Members of the order Saprospirales were enriched from sediment in natural seawater (initial pH > 8), while the family Flavobacteriaceae was favored by acidified seawater (initial pH < 8). Some Flavobacteriaceae members were identified as dominant species in both initial sediment and experiments with acidic wastewater, in which their relative abundance increased with increasing dissolved Cd levels. It could be therefore possible to consider them as bioindicators of metal pollution and/or acidification in marine ecosystems

A Glider-Compatible Optical Sensor for the Detection of Polycyclic Aromatic Hydrocarbons in the Marine Environment

This study presents the MiniFluo-UV, an ocean glider-compatible fluorescence sensor that targets the detection of polycyclic aromatic hydrocarbons (PAHs) in the marine environment. Two MiniFluos can be installed on a glider, each equipped with two optical channels (one PAH is measured per channel). This setup allows the measurement of up to 4 different fluorescent PAHs: Naphthalene, Phenanthrene, Fluorene and Pyrene. Laboratory tests on oil products (Maya crude oil and Diesel fuel) as well as on marine samples near industrial areas (urban harbor and offshore installations) revealed that the concentration of the four PAHs targeted accounted for 62–97% of the total PAH concentration found in samples (∑16 PAHs determined by standard international protocols). Laboratory tests also revealed that for marine applications, the calibration on Water Accommodated Fraction (WAF) of crude oil is more appropriate than the one on pure standards (STD). This is because PAH fluorescence is constituted in large part of alkylated compounds that are not considered with STD calibration. Results from three glider deployments with increasing levels of complexity (a laboratory trial, a field mission in non-autonomous mode and a fully autonomous mission) are also presented. During field deployments, the MiniFluo-glider package was able to detect concentration gradients from offshore marine waters toward the head of a Mediterranean harbor (< 80 ng L−1) as well as hydrocarbon patches at the surface waters of an oil and gas exploitation field in the North Sea (< 200 ng L−1, mainly Naphthalene). It is suggested that using only the WAF calibration, the concentration derived with the MiniFluo agrees within one order of magnitude with the concentration determined by Gas Chromatography coupled with Mass Spectrometry (overestimation by a factor 7 on average). These performances can be improved if the calibration is made with a WAF with PAH proportions similar to the one find in the environment. Finally, it is shown that the use of in situ calibration on water samples collected during the glider deployment, when possible, gives the best results

Patterns and Drivers of UV Absorbing Chromophoric Dissolved Organic Matter in the Euphotic Layer of the Open Ocean

The global distribution of chromophoric dissolved organic matter (CDOM) in the euphotic layer of the Atlantic, Indian, and Pacific oceans (between 35 N and 40 S) was analyzed by absorption spectroscopy during the Malaspina 2010 circumnavigation. Absorption coefficients at 254 nm (a254) and 325 nm (a325), indices (a254/a365) and spectral slopes (between 275 and 295 nm, S275--295) were calculated from the dissolved fraction of the UV absorption spectra to describe the amount and quality of CDOM. Generalized Additive Models (GAMs) were applied to evaluate the relevance of physical and biogeochemical drivers for the variability of CDOM. Besides the low CDOM values, a first division of our data following the Longhurst’s biogeographic classification showed significant differences in CDOM levels among provinces. The lowest values of a254 and a325 were found in the oligotrophic gyres, particularly in the Indian Ocean, and the highest in the upwelling areas, particularly in the Equatorial Pacific. Opposite distributions were obtained for S275--295 and a254/a365, indicative of higher photobleaching in the gyres. The GAM analysis also shows that a254/a365 and S275--295 exhibited inverse relationships with solar radiation, indicating that the biological production of CDOM counteracts photodegradation as solar radiation increases. In summary, whereas photobleaching dictates the vertical distribution of CDOM, Chl a explains the CDOM differences among the photic layer of the tropical and subtropical ocean provinces visited during the circumnavigation.This study was funded by the Ingenio-Consolider project Malaspina 2010 Circumnavigation Expedition (MICINN CSD2008-00077). FI and JO were supported by a fellowship from the “Junta para la Ampliación de Estudios” (JAE-preDOC and JAE-postDOC programs 2011, respectively) from the CSIC

Photochemical alteration of dissolved organic matter and the subsequent effects on bacterial carbon cycling and diversity

Original research paperThe impact of solar radiation on dissolved organic matter (DOM) derived from 3 different sources (seawater, eelgrass leaves and river water) and the effect on the bacterial carbon cycling and diversity were investigated. Seawater with DOM from the sources was first either kept in the dark or exposed to sunlight (4 days), after which a bacterial inoculum was added and incubated for 4 additional days. Sunlight exposure reduced the coloured DOM and carbon signals, which was followed by a production of inorganic nutrients. Bacterial carbon cycling was higher in the dark compared with the light treatment in seawater and river samples, while higher levels were found in the sunlight-exposed eelgrass experiment. Sunlight pre-exposure stimulated the bacterial growth efficiency in the seawater experiments, while no impact was found in the other experiments. We suggest that these responses are connected to differences in substrate composition and the production of free radicals. The bacterial community that developed in the dark and sunlight pre-treated samples differed in the seawater and river experiments. Our findings suggest that impact of sunlight exposure on the bacterial carbon transfer and diversity depends on the DOM source and on the sunlight-induced production of inorganic nutrients.EUROMARINE, CSIC-ESFVersión del editor3,40

Effect of Sub-Lethal Exposure to Ultraviolet Radiation on the Escape Performance of Atlantic Cod Larvae (Gadus morhua)

The amount of ultraviolet (UV) radiation reaching the earth's surface has increased due to depletion of the ozone layer. Several studies have reported that UV radiation reduces survival of fish larvae. However, indirect and sub-lethal impacts of UV radiation on fish behavior have been given little consideration. We observed the escape performance of larval cod (24 dph, SL: 7.6±0.2 mm; 29 dph, SL: 8.2±0.3 mm) that had been exposed to sub-lethal levels of UV radiation vs. unexposed controls. Two predators were used (in separate experiments): two-spotted goby (Gobiusculus flavescens; a suction predator) and lion's mane jellyfish (Cyanea capillata; a “passive" ambush predator). Ten cod larvae were observed in the presence of a predator for 20 minutes using a digital video camera. Trials were replicated 4 times for goby and 5 times for jellyfish. Escape rate (total number of escapes/total number of attacks ×100), escape distance and the number of larvae remaining at the end of the experiment were measured. In the experiment with gobies, in the UV-treated larvae, both escape rate and escape distance (36%, 38±7.5 mm respectively) were significantly lower than those of control larvae (75%, 69±4.7 mm respectively). There was a significant difference in survival as well (UV: 35%, Control: 63%). No apparent escape response was observed, and survival rate was not significantly different, between treatments (UV: 66%, Control: 74%) in the experiment with jellyfish. We conclude that the effect and impact of exposure to sub-lethal levels of UV radiation on the escape performance of cod larvae depends on the type of predator. Our results also suggest that prediction of UV impacts on fish larvae based only on direct effects are underestimations

Application of UV absorbance and fluorescence indicators to assess the formation of biodegradable dissolved organic carbon and bromate during ozonation

This study examined the significance of changes of UV absorbance and fluorescence of dissolved organic matter (DOM) as surrogate indicators for assessing the formation of bromate and biodegradable dissolved organic carbon (BDOC) during the ozonation of surface water and wastewater effluent. Spectroscopic monitoring was carried out using benchtop UV/Vis and fluorescence spectrophotometers and a newly developed miniature LED UV/fluorescence sensor capable of rapidly measuring UVA280 and protein-like and humic-like fluorescence. With the increase of O3/DOC mass ratio, the plots of BDOC formation were characterized of initial lag, transition slope and final plateau. With the decrease of UV absorbance and fluorescence, BDOC concentrations initially increased slowly and then rose more noticeably. Inflection points in plots of BDOC versus changes of spectroscopic indicators were close to 35 e45% loss of UVA254 or UVA280 and 75e85% loss of humic-like fluorescence. According to the data from size exclusion chromatography (SEC) with organic carbon detection and 2D synchronous correlation analyses, DOM fractions assigned to operationally defined large biopolymers (apparent molecular weight, AMW>20 kDa) and medium AMW humic substances (AMW 5.5e20 kDa) were transformed into medium-size building blocks (AMW 3e5.5 kDa) and other smaller AMW species (AMW<3 kDa) associated with BDOC at increasing O3/DOC ratios. Appreciable bromate formation was observed only after the values of UVA254, UVA280 and humic-like fluorescence in O3-treated samples were decreased by 45 e55%, 50e60% and 86e92% relative to their respective initial levels. No significant differences in plots of bromate concentrations versus decreases of humic-like fluorescence were observed for surface water and wastewater effluent samples. This was in contrast with the plots of bromate concentration versus UVA254 and UVA280 which exhibited sensitivity to varying initial bromide concentrations in the investigated water matrixes. These results suggest that measurements of humic-like fluorescence can provide a useful supplement to UVA indices for characterization of ozonation processes