Autochthonous Optical Signals in CDOM from Phytoplankton Culture and Open Ocean Observations

Chromophoric dissolved organic matter (CDOM) is ubiquitous in the marine environment, however information regarding the origin and optical and chemical signals of open ocean autochthonous CDOM is limited. A potential source of CDOM is from phytoplankton-derived particulate organic matter (POM) transformed through microbial degradation and disaggregation. Changes in planktonic base-extracted POM (BEPOM) absorbance and fluorescence signals were tracked through growth and aggregate formation for a cultured diatom (Pseudo-nitzschia spp.). Laboratory observations were combined with open-ocean CDOM and BEPOM optical measurements from two cruises in the Mid-Atlantic Bight, in addition to bacterial production, organic carbon concentrations, and stable carbon isotope values. A five-component parallel factor analysis (PARAFAC) model from coastal BEPOM samples was applied to our samples to identify components within our samples. Preliminary results of BEPOM excitation-emission matrices (EEMs) for both culture and field data exhibited a “three peak” pattern likely representing the aromatic amino acid, tryptophan, and quinone-like fluorescence, suggesting intramolecular charge transfer between electron donors and acceptors—perhaps mediated by aggregate formation. Mid-Atlantic Bight CDOM EEMs were dominated by an excitation peak at ca. 260 nm consistent with tyrosine fluorescence, indicating the ephemeral nature of the BEPOM signal. Further culture and field studies will provide additional insights into the cycling and sources of organic matter in open ocean environments.