Distinguishing between terrestrial and autochthonous organic matter sources in marine environments using fluorescence spectroscopy

Abstract

The optical properties of chromophoric dissolved organic matter (CDOM) are frequently used as tracers of water masses in bays and estuaries but present unique challenges in the ocean due to the small quantities of organic matter present and the similarities between spectra from coastal and offshore environments. Samples collected on trans-oceanic cruises in the Pacific and Atlantic oceans were used to investigate the optical characteristics of dissolved organic matter in waters with limited freshwater influence (salinity > 30). Parallel Factor Analysis (PARAFAC) of fluorescence spectra revealed that coastal and oceanic dissolved organic matter (DOM) fluorescence could be separated into at least eight separate components: 4-5 humic-like and 3-5 protein-like signals. Two of the humic components were identified as representing terrestrial organic matter and their signals could be traced in the open ocean (Pacific and Atlantic) at levels of approximately 1.5% of riverine concentrations. An additional humic component, traditionally identified as the "marine" or "M" peak, was found to be both sourced from land and produced in the ocean. These results demonstrate that the supply, mixing and removal of terrestrial organic matter in oceanic waters can be observed with relatively simple measurement techniques, suggesting that fluorescence spectroscopy could play a useful role in future studies of the origin and fate of DOM in oceanic environments.