Catherine Guigue

Effect of natural iron fertilization on carbon sequestration in the Southern Ocean

The availability of iron limits primary productivity and the associated uptake of carbon over large areas of the ocean. Iron thus plays an important role in the carbon cycle, and changes in its supply to the surface ocean may have had a significant effect on atmospheric carbon dioxide concentrations over glacial–interglacial cycles. To date, the role of iron in carbon cycling has largely been assessed using short-term iron-addition experiments. It is difficult, however, to reliably assess the magnitude of carbon export to the ocean interior using such methods, and the short observational periods preclude extrapolation of the results to longer timescales. Here we report observations of a phytoplankton bloom induced by natural iron fertilization—an approach that offers the opportunity to overcome some of the limitations of short-term experiments. We found that a large phytoplankton bloom over the Kerguelen plateau in the Southern Ocean was sustained by the supply of iron and major nutrients to surface waters from iron-rich deep water below. The efficiency of fertilization, defined as the ratio of the carbon export to the amount of iron supplied, was at least ten times higher than previous estimates from short-term blooms induced by iron-addition experiments. This result sheds new light on the effect of long-term fertilization by iron and macronutrients on carbon sequestration, suggesting that changes in iron supply from below—as invoked in some palaeoclimatic and future climate change scenarios—may have a more significant effect on atmospheric carbon dioxide concentrations than previously thought.

Identification and quantification of known polycyclic aromatic hydrocarbons and pesticides in complex mixtures using fluorescence excitation-emission matrices and parallel factor analysis.

Polycyclic aromatic hydrocarbons (PAHs) and pesticides are among the most widespread organic contaminants in aquatic environments. Because of their aromatic structure, PAHs and pesticides have intrinsic fluorescence properties in the ultraviolet/blue spectral range. In this study, excitation-emission matrix (EEM) fluorescence spectroscopy and parallel factor (PARAFAC) analysis were used to characterise and discriminate fluorescence signatures of nine PAHs and three pesticides at the μg L(-1) level in the presence of humic substances (0.1-10 mgCL(-1)). These contaminants displayed a diversity of fluorescence signatures regarding spectral position (λEx: 220-335 nm, λEm: 310-414 nm), Stokes shift (39-169 nm) and number of peaks (1-8), with detection limits ranging from 0.02 to 1.29μgL(-1). The EEM/PARAFAC method applied to mixtures of PAHs with humic substances validated a seven-component model that included one humic-like fluorophore and six PAH-like fluorophores. The EEM/PARAFAC method applied to mixtures of pesticides with humic substances validated a six-component model that included one humic-like fluorophore and three pesticide-like fluorophores. The EEM/PARAFAC method adequately quantified most of the contaminants for humic substance concentrations not exceeding 2.5 mg CL(-1). The application of this method to natural (marine) samples was demonstrated through (1) the match between the Ex and Em spectra of PARAFAC components and the Ex and Em spectra of standard PAHs, and (2) the good linear correlations between the fluorescence intensities of PARAFAC components and the PAH concentrations determined by GC-MS.

Utilization of a submersible UV fluorometer for monitoring anthropogenic inputs in the Mediterranean coastal waters.

We evaluated the performances of a submersible ultraviolet fluorometer (EnviroFlu-HC, TriOS Optical Sensors) dedicated to the real time measurement of polycyclic aromatic hydrocarbons (PAHs) in the aquatic media. We conducted calibration experiments and in situ measurements in the coastal Mediterranean Sea. We found that the EnviroFlu-HC was not strictly specific to PAHs, even though it exhibited the highest sensitivity for phenanthrene, but could response to tryptophan-like material as well, and in a much less extent, to humic substances. The sensor signal showed great spatial and temporal variations in clean and polluted sites, with likely a high contribution of PAHs in the harbors, and a high contribution of tryptophan-like and humic-like materials in the sewage effluent. We conclude that the EnviroFlu-HC is a good tool for monitoring anthropogenic inputs in the coastal waters, although its utilization should be combined to other fluorescence measurements to improve the information about the nature of the aromatic compounds detected.

Spatial and seasonal variabilities of dissolved hydrocarbons in surface waters from the Northwestern Mediterranean Sea : results from one year intensive sampling

Dissolved aliphatic hydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs) were analysed from surface water collected in continental, harbour and off-shore marine sites from Marseilles coastal area (Northwestern Mediterranean Sea) from February 2011 to February 2012. AH and PAH concentrations were in the range of 0.04-0.53 μgl(-1) and 8.1-405 ngl(-1), respectively. They both displayed seasonal and spatial variations in their concentrations and molecular composition. The lowest AH concentrations were found in summer and the highest PAH concentrations in winter. Both natural and anthropogenic (pyrogenic and petrogenic) hydrocarbon sources were identified. In winter, concentrations and composition patterns highlighted an increase in the signature of unburned and combusted fossil fuels, while they suggested an enhancement of weathering processes in summer months. Hydrocarbon inputs to the dissolved phase seemed to originate mainly from the atmosphere and the Rhône River. Hydrocarbon additional sources were identified only at the harbour site, emphasising the intense shipping traffic and industrial activities occurring in one of the most important Mediterranean harbours. This study underscores the strong dynamics of dissolved hydrocarbons and the uncoupling of the sources, transport and removing processes affecting AHs and PAHs. It also demonstrates the pertinence of taking this dynamics into account for the budget assessments of organic pollutants in coastal environments.

Occurrence and distribution of hydrocarbons in the surface microlayer and subsurface water from the urban coastal marine area off Marseilles, Northwestern Mediterranean Sea

Aliphatic (AHs) and polycyclic aromatic hydrocarbons (PAHs) were analyzed in dissolved and particulate material from surface microlayer (SML) and subsurface water (SSW) sampled at nearshore observation stations, sewage effluents and harbour sites from Marseilles coastal area (Northwestern Mediterranean) in 2009 and 2010. Dissolved and particulate AH concentrations ranged 0.05-0.41 and 0.04-4.3 μg l(-1) in the SSW, peaking up to 38 and 1366 μg l(-1) in the SML, respectively. Dissolved and particulate PAHs ranged 1.9-98 and 1.9-21 ng l(-1) in the SSW, amounting up 217 and 1597 ng l(-1) in the SML, respectively. In harbours, hydrocarbons were concentrated in the SML, with enrichment factors reaching 1138 for particulate AHs. Besides episodic dominance of biogenic and pyrogenic inputs, a moderate anthropisation from petrogenic sources dominated suggesting the impact of shipping traffic and surface runoffs on this urbanised area. Rainfalls increased hydrocarbon concentrations by a factor 1.9-11.5 in the dissolved phase.

Isolation of alkane‐degrading bacteria from deep‐sea Mediterranean sediments

Aims:  To isolate and identify alkane‐degrading bacteria from deep‐sea superficial sediments sampled at a north‐western Mediterranean station.

Triacylglycerol biodegradation experiment in marine environmental conditions: definition of a new lipolysis index

Abstract An experiment on the biodegradation of dissolved triacylglycerol (TG) by a natural Antarctic bacterial community was performed at in situ temperature, in the dark. The lipid classes and their metabolites resulting from the TG degradation were identified and quantified by TLC/FID Iatroscan analysis. TG was hydrolysed rapidly by bacteria ( K =−0.22 d −1 ), whereas metabolites were accumulated at different rates. An increase of phospholipids (PL) was observed, related to the growth of bacteria. This experiment confirmed that in the marine environment, diglycerides (DG), monoglycerides (MG) and free fatty acids (FFA) are released by the hydrolysis of acyl-lipids. We define the Lipolysis Index (LI) as the ratio of the sum of the metabolites resulting from the acyl-lipid degradation to the sum of the acyl-lipids present in the medium. We propose to use this lipolysis index (LI) as a new tool which characterises the degradation stage of labile organic matter in natural sea water samples.

Hydrocarbons in a coral reef ecosystem subjected to anthropogenic pressures (La Réunion Island, Indian Ocean)

The La Saline fringing reef, which is the most important coral reef complex of La Reunion Island, (south- western Indian Ocean), is subjected to anthropogenic pressures through river and groundwater inputs. Salinity and biogeochemicalparameters(silicates,nitrates,dissolvedorganiccarbon,chlorophyll-a),aswellasaliphatichydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs) were analysed in particulate and dissolved material from ground- waters,rivers,harbour,backreef,forereefandoceanicwatersintheLaSalinereefareaduringtherainyseason(February- March 2012). Particulate and dissolved AH concentration ranges were 0.07-144 and 0.06-0.58 m gL � 1 respectively. Particulate and dissolved PAH concentrations ranges were 4.3-326 and 28-350 ng L � 1 respectively. AHs, dominated by nC15, nC17, nC18 compounds or nC26, nC27, nC29, nC31 compounds, were mainly of biogenic origin (phytoplankton, bacteria, higher-plant debris) although some anthropogenic (petroleum inputs) signatures were recorded in the dissolved phase from the harbour and fore reef areas. PAHs, dominated by two- to three-ring compounds and their alkylated homologues, reflected unburned petroleum inputs, but probably also biogenic sources. From the distribution of salinity, biogeochemical parameters and hydrocarbons, we found that inland waters flowed mainly in the surface and in the southern part of reef waters and that particulate PAHs allowed tracking these inland water intrusions in fore reef waters. Finally, this pilot study highlights the uncoupling between the dynamics of AHs and PAHs in tropical environments. Additionalkeywords: aliphatichydrocarbons,groundwaters,LaSalinefringingreef,polycyclicaromatichydrocarbons, tropical environment.

Performance of the MiniFluo-UV sensor for monitoring ocean and coastal environments

Understanding the biogeochemical functioning of the ocean requires high frequency recordings of DOM (Dissolved Organic Matter) descriptors that traditional tools such chromatography cannot provide. For 10 years, the technological developments of fluorescence sensor try to cover this need. Indeed, optical properties allow to properly characterizing DOM and can be acquired at high frequency. In this context, our laboratory developed the MiniFluo-UV sensor, a prototype of miniaturized submersible fluorometers for the detection of aromatic compounds that fluoresce in the UV domain. The qualification of the sensor consisted of measurement of drift, linearity, repeatability, sensitivity to light, temperature and pressure, and detection limits of quantification of phenanthrene and tryptophan in standard solution. Validation was made by comparing measurements of phenanthrene concentrations in crude oil WSF by means of the MiniFluo and different fluorimeters. In this presentation, we show results of deployments of this MiniFluo-UV sensor in two distinct areas, 1) the North Western Mediterranean during the continuous monitoring of the surface water layer in the Gulf of Lion (DEWEX cruise, winter and spring 2013) and 2) the coastal marine area of Marseille bay heavily impacted by urban activities. The pattern of raw counts enabled to distinguish interesting distributions of DOM in relation to hydrological features and spring biological production in the Gulf of Lion. It also revealed accumulations of contaminants in marine areas under anthropic pressure.

Utilization of a Submersible Ultra-Violet Fluorometer for Monitoring Anthropogenic Inputs in the Mediterranean Coasts

The Mediterranean Sea coasts are subject to a strong anthropogenic pressure because of an intensification of urban, industrial, agricultural, and tourist activities. This anthropogenic pressure is reflected in the direct (from coastal sources) and indirect (via rivers) discharge of terrigenous materials and pollutants. These contributions promote transformations of ecosystems and associated biogeochemical cycles.