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

Cosmological constraints from lensing statistics and supernovae on the cosmic equation of state

We investigate observational constraints from lensing statistics and high-z type Ia supernovae on flat cosmological models with nonrelativistic matter and an exotic fluid with equation of state, $p_x=(m/3 -1)\rho_x$. We show that agreement with both tests at the 68% confidence level is possible if the parameter $m$ is low ($m \lesssim 0.85$) and $0.24 \lesssim \Omega_{m0} \lesssim 0.38$ with lower values of $\Omega_{m0}$ corresponding to higher $m$. We find that a conventional cosmological constant model with $\Omega_{m0}\simeq 0.33$ is the best fit model of the combined likelihood.Comment: 7 pages, 4 postscript figures, revtex, submitted to Phys. Rev.

Marine bacteria as a source of dissolved fluorescence in the ocean

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1990.Includes bibliographical references.by Paula G. Coble.Ph.D

Colored Dissolved Organic Material Increases Resiliency of Coral Reefs by Controlling Exposure to UVR

Although mass coral bleaching events are generally triggered by high seawater temperatures, experiments have demonstrated that corals and reef-dwelling foraminifers bleach more readily when exposed to high energy, short wavelength solar radiation (blue, violet and ultraviolet [UVR]: . ~ 280 - 490 nm). In seawater, colored dissolved organic matter (CDOM), also called gelbstoff, preferentially absorbs these shorter wavelengths, which consequently bleach and degrade the CDOM. Alteration and destruction of watershed and coastal wetlands have reduced natural sources of CDOM that are tidally flushed into reefal waters. We have measured absorption of UVR and UV irradiance at various reefs in the Florida Keys that differ in distance from shore and the degree of anthropogenic development of the adjacent shoreline. Our results show that reefs associated with intact shorelines tend to be exposed to lower intensities of UVR than reefs associated with developed shorelines. Absorption due to CDOM at 320 nm (ag320) was less variable at reefs associated with intact shorelines, and higher at inshore reefs compared to offshore reefs. UVR is attenuated more quickly at inshore than offshore, clear-water reefs at similar depths. Spectral slope of ag, S, was generally greater at offshore sites, indicating a higher degree of photo bleaching of CDOM

MAA-Like Absorbing Substances in Florida Keys Phytoplankton Vary with Distance from Shore and CDOM: Implications for Coral Reefs

Colored dissolved organic material (CDOM) is the primary attenuator of low wavelength visible and ultraviolet radiation (UVR, 290-400). Phytoplankton produce UV-absorbing pigments called Mycosporine-like Amino Acids (MAAs), in response to UV stress. MAA-like absorption peaks in particulate material, including phytoplankton, were measured at 24 locations differing in distance from the shoreline along the Florida, USA reef tract. Elevated MAA-like absorption peaks were detected: 1) only in surface samples, 2) most consistently at offshore sites with low coral cover, and 3) when absorption due to CDOM was low. In addition, UVB attenuation increased as absorption due to CDOM increased, the depth at which UVB irradiance was attenuated to 10% of its surface value increased exponentially as absorption due to CDOM decreased, and coral cover decreased with decreasing near-surface attenuation of UVB. CDOM serves as photo-protection and MAA-like absorption may indicate the potential for photo-oxidative stress in coral reef ecosystems. MAA-like absorbance peaks in phytoplankton suggest photic stress in coral reefs

Influence of Extreme Storm Events on West Florida Shelf CDOM Distributions

Colored Dissolved Organic Matter (CDOM) distribution and signatures provide vital information about the amount and composition of organic material in aquatic environments. This information is critical for deciphering the sources and biogeochemical pathways of organic carbon, and thus vital to the understanding of carbon cycling and budgets. Waters of the West Florida Shelf are heavily influenced by many river systems on Florida\u27s Gulf Coast that, to the first order, control CDOM distributions on the shelf. Three storm events during 2004 and 2005 (Hurricane Charley, Hurricane Wilma, and a Winter Storm) profoundly altered the typical distribution of CDOM fluorescence and absorption properties on the Southern West Florida Shelf. Seasonal surveys revealed that changes in the underwater light field as a result of major hurricanes and resuspension events are linked closely with a number of factors prior to a storm\u27s passing such as the presence of persistent blooms, rainfall and discharge. Additionally, storm track and wind direction were found to play a significant role in CDOM signatures

Multispectral In-situ Measurements of Organic Matter and Chlorophyll Fluorescence in Seawater: Documenting the Intrusion of the Mississippi River Plume in the West Florida Shelf

We performed multispectral in-situ fluorescence measurement of colored dissolved organic matter and chlorophyll in surface water of the West Florida Shelf using West Labs Spectral absorption and Fluorescence Instrument (SAFIre). Continuous measurements underway allowed us to simultaneously map the dispersion of riverine organic material and chlorophyll on the shelf. By using two fluorescence emission ratios we were able to differentiate between riverine and marine CDOM. Our data also showed unusually high concentrations of CDOM offshore. These were attributed to an intrusion of the Mississippi River Plume. We performed limited comparisons between in-situ chlorophyll concentrations measured with SAFIre and chlorophyll values obtained from SeaWiFS satellite data using OC4 and MODIS algorithm. Our results show that, although both algorithms overestimated chlorophyll, MODIS performed better than OC4, particularly in areas with high CDOM concentrations. Analysis of the relationship between chlorophyll and CDOM concentrations within the study area showed regional variability causes by differences in river source