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Evidence for the production of marine fluorescence dissolved organic matter in coastal environments and a possible mechanism for formation and dispersion
Citation:
MILBRANDT, E. C., P. G. COBLE, R. N. CONMY, A. J. MARTIGNETTE, AND J. SIWICKE. Evidence for the production of marine fluorescence dissolved organic matter in coastal environments and a possible mechanism for formation and dispersion. LIMNOLOGY AND OCEANOGRAPHY. American Society of Limnology and Oceanography, Lawrence, KS, 55(5):2037-2051, (2010).
Impact/Purpose:
The objective is to publish findings on the production of new marine DOM in shallow waters combined with evaporative conditions thus forming high CDOM, high salinity water masses. Evidence is reported from several cruises on the West Florida Shelf (WFS) and time series data from a shallow, southwest Florida estuary. Presented are CDOM fluorescence results which have implications for characterizing the role of DOM as a contributor to water clarity and ecosystem health.
Description:
A positive linear relationship between salinity and fluorescent dissolved organic matter (FDOM) was observed on several occasions along the West Florida shelf at salinities greater than 36.5. This represents a departure from the typical inverse relationship between FDOM and salinity observed in most coastal regions caused by the mixing of riverine FDOM with clear oceanic water. Three-dimensional excitation–emission matrices showed that the high-salinity, high-FDOM water had blue-shifted spectra characteristic of autochthonous, marine FDOM, with peak M concentrations eight times higher than previously reported for seawater. The blue-shifted fluorescence endmember at high salinity was clearly distinguishable from a photobleached FDOM endmember. A high-resolution time series collected in a shallow embayment with significant Gulf of Mexico influence supplemented cruise data and provided a possible mechanism for the formation of high-salinity, high-FDOM water. During a dry period of spring tides, high-salinity, high-FDOM water was exported at ebb tide and lower salinity, low-FDOM water was imported during flood tide. During neap tide, FDOM and salinity demonstrated no evidence of either export or dilution from incoming seawater. After a significant rain event, a more typical inverse relationship between salinity and FDOM was observed. Production of FDOM-rich water in shallow embayments has not been observed previously. This is likely an important source of organic matter and dispersion of this material may explain observations of a high-salinity, high-FDOM water in adjacent coastal regions.