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GCE III - Key Finding in 2017

    Using high resolution mass spectrometry to track dissolved organic matter through estuaries

    Rivers are important sources of terrestrially derived organic matter to coastal systems. However, tracking the fate of this material can be challenging because it is composed of multiple compounds that can be altered by biological, chemical, and physical processes as it is transported downstream. Medeiros et al. (2015) used ultrahigh resolution mass spectrometry to characterize spatial and temporal variability in dissolved organic matter (DOM) sources in estuaries in the GCE domain. They found that DOM composition was strongly modulated by river discharge at monthly scales, with high river flow leading to significant increases in the terrigenous signature of the DOM throughout the estuary. During a drought year, riverine and estuarine DOM had a distinct molecular signature indicative of marsh-derived compounds. In a related study, Medeiros et al. (2017) evaluated the seasonal patterns of terrigenous DOM in the South Atlantic Bight (SAB). They found that DOM with a strong terrigenous signature was restricted to a coastal band early in the year, and extended further offshore to the shelf break in late spring. As part of this effort they demonstrated that optical absorbance could be used as a proxy for terrestrially-derived DOM in the SAB, which could then be scaled up with remote sensing (Fig. 1). Finally, Medeiros et al. (2017) reported on incubations conducted to examine microbially mediated transformations of DOM. They found a microbial preference for degradation of compounds of marine origin, which shifted the remaining material towards a stronger terrigenous signature. These types of studies help to improve our understanding of the oceanic fate of terrigenous DOM and its role in the global carbon cycle.


    Fig. 1 (a) Surface salinity, (b) estimated % terrigenous based on the spectral slope coefficient of chromophoric DOM in the 279-295 nm range, and (c) surface DOC concentration during April 2014 research cruise. From Medeiros et al. 2017.


This material is based upon work supported by the National Science Foundation under grants OCE-9982133, OCE-0620959, OCE-1237140 and OCE-1832178. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.