Seasonal dynamics of light absorption by chromophoric dissolved organic matter (CDOM) in the NW Mediterranean Sea (BOUSSOLE site) |
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| Institution: | 1. Sorbonne Universités, UPMC Univ Paris 06, CNRS, Observatoire Océanologique de Villefranche (OOV), Laboratoire d''Océanographie de Villefranche (LOV), 181 Chemin du Lazaret, 06 230 Villefranche-sur-Mer, France;2. Marine Physical Laboratory, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0238, USA;1. CSIRO Oceans and Atmosphere, Hobart, Australia;2. Climate Change Cluster, University of Technology Sydney, Australia;3. CSIRO Oceans and Atmosphere, Brisbane, Australia;4. Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, Australia;5. Sydney Institute of Marine Science, Mosman, Australia;1. Plymouth Marine Laboratory (PML), Prospect Place, The Hoe, Plymouth PL1 3DH, UK;2. National Centre for Earth Observation, PML, Plymouth PL1 3DH, UK;3. Bayworld Centre for Research & Education, PO Box 7296, Roggebaai 8012, South Africa;4. Marine Research Institute, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa;5. Centro de Oceanografia, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal;6. Oceans & Coastal Research, Department of Environmental Affairs, PO Box 52126, Victoria & Alfred Waterfront, Cape Town 8002, South Africa;1. Borneo Marine Research Institute, University of Malaysia of Sabah, Sabah, Malaysia;2. Centre for Geography and Environmental Science, College of Life and Environmental Sciences, University of Exeter, Penryn, Cornwall, United Kingdom;3. Faculty of Science and Marine Environment, University of Malaysia Terengganu, Terengganu, Malaysia;4. Marine Research Laboratory (MEAL), Faculty of Fishery and Marine Science, Padjadjaran University, Jatinangor, Indonesia |
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| Abstract: | We analyze a two-year time-series of chromophoric dissolved organic matter (CDOM) light absorption measurements in the upper 400 m of the water column at the BOUSSOLE site in the NW Mediterranean Sea. The seasonal dynamics of the CDOM light absorption coefficients at 440 nm (acdom(440)) is essentially characterized by (i) subsurface maxima forming in spring and progressively reinforcing throughout summer, (ii) impoverishment in the surface layer throughout summer and (iii) vertical homogeneity in winter. Seasonal variations of the spectral dependence of CDOM absorption, as described by the exponential slope value (Scdom), are characterized by highest values in summer and autumn at the surface and low values at the depths of acdom(440) subsurface maxima or just below them. Variations of acdom(440) are likely controlled by microbial digestion of phytoplankton cells, which leads to CDOM production, and by photochemical destruction (photobleaching), which leads to CDOM degradation. Photobleaching is also the main driver of Scdom variations. Consistently with previous observations, acdom(440) for a given chlorophyll a concentration is higher than expected from Case I waters bio-optical models. The total non-water light absorption budget shows that surface waters at the BOUSSOLE site are largely dominated by CDOM during all seasons but the algal bloom in March and April. These results improve the knowledge of CDOM absorption dynamics in the Mediterranean Sea, which is scarcely documented. In addition, they open the way to improved algorithms for the retrieval of CDOM absorption from field or satellite radiometric measurements. |
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| Keywords: | Chromophoric dissolved organic matter Light absorption time-series Photobleaching Light absorption budget Mediterranean Sea |
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