The colloidal size spectrum of CDOM in the coastal region of the Mississippi Plume using flow field-flow fractionation

Abstract

Chromophoric dissolved organic matter (CDOM) is a major component of the total dissolved organic matter in seawater, and it can interfere significantly with oceanographic remote sensing in nearshore waters. Coastal marine CDOM comprises an undefined, likely rapidly changing mixture of terrestrially and marine-derived substances. Flow Field-Flow Fractionation (FlFFF) offers a novel approach for separating the colloidal (high molecular weight) fraction of CDOM into broad size continuums that can offer insights to the characteristics and reactivity of CDOM constituents. FlFFF analyses of seawaters in and around the Mississippi Plume were performed during high and low flow conditions and the results compared to analyses of phytoplankton cultures and waters from a coastal estuary having low freshwater inputs. FlFFF fractograms displayed major differences in the size distribution of CDOM between offshore in the Gulf of Mexico (GOMex) and the Mississippi River plume. Colloidal size distributions in nearshore surface waters out of the immediate influence of the Mississippi Plume contained a mixture of features seen in offshore waters, plume waters, and in phytoplankton cultures. Plume waters had a high abundance of larger colloidal phases but continued dilution with coastal waters led to preferential losses of mid-sized colloidal matter. Colloidal size spectra in offshore waters of the GOMex during spring were similar to that observed in estuarine waters after the spring bloom. These preliminary findings suggest that the colloidal size spectrum of CDOM may provide information on its provenance and the relative mixtures of terrestrial and marine components.