Dissolved Organic Matter in Alaskan Coastal Waters: Dynamics of Riverine Discharge Effects on the Quantity and Quality of CDOM and DOC

Michael G Novak, NASA Goddard Space Flight Center, Greenbelt, MD, United States, Peter J Hernes, University of California - Davis, Davis, United States, Antonio Mannino, NASA Goddard Space Flight Center, Ocean Ecology Laboratory, Greenbelt, MD, United States, Robert G Spencer, Florida State University, Earth, Ocean and Atmospheric Science, Tallahassee, United States and Maria Tzortziou, Columbia University of New York, New York, United States
Several recent studies have shown temperatures in the Arctic region to be warming twice as fast as the global average. These warming trends are influencing the inception of ice breakup as well as thawing permafrost, which in turn affects the timing, extent, and composition of freshwater input into surrounding seas. Dissolved Organic Matter (DOM) transported by Arctic rivers is comprised of high levels of chromophoric dissolved organic matter (CDOM) and dissolved organic carbon (DOC). The former characterized by an optical absorption signal in the visible and ultraviolet spectrum whose magnitude and spectral shape have been shown to have a strong relationship with the quantity and quality of the latter. Arctic rivers exhibit sharp seasonal discharge changes with rapid pulses of terrestrial input into adjacent Arctic surface waters which influences the biogeochemistry and the optical signature of these regions. This study analyzed in situ field data collected during the transition from the spring ice breakup to lower summer flow conditions across a broad salinity gradient from the Yukon River Delta waters to the adjacent Norton Sound in 2018 and 2019. These results are compared with measurements along Alaska’s North Slope between the deltas of two small river systems, the Hulahula and Jago rivers, coastal lagoons and Beaufort Sea shelf waters. Not surprisingly, the DOM flowing out of the Yukon River is significantly higher in DOC and CDOM absorption than from the North Slope river systems. DOC concentration and CDOM absorption is significantly greater during high river discharge. The relationships identified were used to develop optical proxies for DOC concentration and DOM composition and further compared to stream gauge data to elucidate the effects of river flow and seasonality.