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

Iron-binding by dissolved organic matter in the Western Tropical South Pacific Ocean (GEOTRACES TONGA cruise GPpr14)

Iron (Fe) is an essential micronutrient for phytoplankton growth, but its scarcity in seawater limits primary productivity across much of the ocean. Most dissolved Fe (DFe) in seawater is complexed with Fe-binding organic ligands, a poorly constrained fraction of dissolved organic matter (DOM), which increase Fe residence time and impact Fe bioavailability. Here, we present the conditional concentration (LFe) and binding-strength (log KFe'Lcond) of Fe-binding ligands in the Western Tropical South Pacific (WTSP) Ocean during the GEOTRACES TONGA cruise (GPpr14). The transect crossed the Lau basin, a region subject to shallow hydrothermal Fe inputs that fuel intense diazotrophic activity, the oligotrophic South Pacific gyre, and the Melanesian basin. Organic speciation was analyzed by competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-AdCSV) using salicylaldoxime at 25 µM. We found a high mean LFe of 5.2 ± 1.2 nMeqFe (n = 103) across the entire transect, predominantly consisting of intermediate strength L2 ligands (84%; mean log KFe'Lcond of 11.6 ± 0.4), consistent with humic-like substances. DFe correlated with the humic-like component of the fluorescent DOM (HS-like FDOM), yet the electroactive Fe-binding humic-like substances (LFeHS) accounted for only 20 ± 13% of LFe in the mixed layer and 8 ± 6% in deep waters. Ligands were in large excess compared to DFe (mean excess ligand eLFe = 4.6 ± 1.1 nMeqFe), suggesting poor stabilization of DFe inputs. High LFe (up to 9 nMeqFe) in samples close to hydrothermal sites could be due to detoxification strategies from plankton communities toward hydrothermally-fueled toxic trace metals other than Fe, with an apparent dilution of the DOM from the Lau basin into neighboring regions. We also observed a different peak potential of the Fe salicylaldoxime complex detected by CLE-AdCSV between the Lau and Melanesian basins, and between surface and deep waters. To our knowledge, this change in potential has not previously been reported; whether this represents a novel detection of specificities in DOM composition merits further investigation. Competition between Fe and competing metals for ligand binding sites could favor DFe oxidation and precipitation near hydrothermal vents and explain the absence of strong Fe stabilization in the WTSP

A simple and highly reproducible technique to extract the 14CO2 resulting from respiration of 14C-labeled seawater samples

International audienceProduction of 14CO2 from water samples amended with 14C-labeled molecules allows estimation of the mineralization rates of a variety of organic compounds. Diverse protocols have been already proposed for 14CO2 extraction and trapping. Yet, efficiency of carbon dioxide recovery greatly varies and, despite the application of operators, data from duplicate samples are often divergent. In order to propose a standardized protocol and to avoid the main source of artifacts, we suggest keeping the trapping agent for 14CO2 directly into a 20 ml scintillation vial hanging in the degassing bottle. To validate this protocol, we plotted the radioactivity (disintegration per minute) due to 14CO2 recovered after acidification of 42 seawater samples supplemended with sodium (14C)-bicarbonate (NaH14CO3) against the actual radioactivity of the corresponding added bicarbonate solutions. Efficiency of this protocol results satisfactory; as for these 42 assays the percentage of recovery is equal to 99% with a very low variability (±1%, p ¼ 0.05)

Penetration of ultraviolet radiation in the marine environment. A review.

UV radiation (UVR) is a significant ecological factor in the marine environment that can have important effects on planktonic organisms and dissolved organic matter (DOM). The penetration of UVR into the water column is likely to change in the near future due to interactions between global warming and ozone depletion. In this study we report underwater instruments employed for the measurement of UVR and we review data dealing with the depth of UVR penetration in different oceanic areas including the open ocean, Antarctic waters and coastal waters. We provide the 10% irradiance depth (Z10%) for UV-A and UV-B as well as for DNA damage effective dose (DNA), which we calculated from the values of diffuse attenuation coefficients or vertical profiles reported in the literature. We observe a clear distinction between open ocean (high Z10%, no variation in the ratio UV-B/UV-A), Antarctic waters (increase in the ratio UV-B/UV-A during ozone hole conditions) and coastal waters (low Z10%, no variation in the ratio UV-B/UV-A). These variations in the penetration of UVR could lead to differences in the relative importance of photobiological/photochemical processes. We also compare in this study the penetration of UV-B (unweighted and weighted by the Setlow action spectrum) and DNA damage effective dose