OPTICAL PROPERTIES OF BLACK SEA DISSOLVED ORGANIC MATTER: ORIGIN AND IMPLICATIONS
The Black Sea is the largest anoxic basin on Earth, characterized by salinities of ~17-22 resulting from mixing between Mediterranean seawater (salinity ≈ 36) and freshwater. Dissolved organic carbon (DOC) concentrations (~120-200 μM) are ~2.5 times higher than in the open ocean and Mediterranean Sea; previous studies suggested that input of terrigenous DOC from rivers is responsible for the relatively high concentrations. To obtain information on the basin's DOC composition (e.g., humic- or protein-like) and predominant origin (i.e., terrigenous or marine), the optical properties (absorbance and fluorescence) of chromophoric dissolved organic matter (CDOM) were measured in 111 samples across the Black Sea salinity, redox and DOC gradients. In the basin's oxic layer (upper ~100 m), CDOM correlates with DOC, suggesting that they are controlled by the same processes. In the underlying anoxic layer (lower ~2000 m), DOC varies by ~10% while CDOM ~doubles, correlating well with H2S and nutrients. These findings indicate that a fraction of in situ DOC is transformed by microbes in the anoxic water, altering its CDOM composition, and/or that composition changes as a result of external inputs (e.g., sinking particles) with little net concentration change. Our results provide information on the origin and composition of DOC fractions across the Black Sea's salinity and redox gradients, as well as providing insights on the past, present and future ocean, DOC-induced climate changes and the global carbon cycle.
Margolin, A. R., Rosenstiel School of Marine and Atmospheric Science, University of Miami, USA, email@example.com
Gonnelli, M., Biophysics Institute, CNR, Pisa, Italy, firstname.lastname@example.org
Hansell, D. A., Rosenstiel School of Marine and Atmospheric Science, University of Miami, USA, email@example.com
Santinelli, C., Biophysics Institute, CNR, Pisa, Italy, firstname.lastname@example.org
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