Arctic Biogeochemical and Optical Properties of Suspended Particles from River Deltas to Coastal Seas

Human-induced climate change has brought about rapid and sustained alterations of Arctic seas and watersheds. Thawing permafrost along with changing vegetation and river discharge will undoubtedly continue to alter the composition and fluxes of nutrients, organic matter and sediments entering nearshore waters and coastal seas. Our work aims to characterize changes in concentrations, composition and fluxes of organic and inorganic materials between the river head of tides and coastal seas of our study areas which include the Yukon River-delta-Norton Sound system as our primary study site and Arctic National Wildlife Refuge (ANWR) rivers-lagoons-Beaufort Sea system. The Yukon River watershed drains vast areas of Arctic tundra and taiga forests while ANWR rivers drain largely Arctic tundra. Little is known about the particle composition and concentration across the salinity gradients between these Arctic river deltas and coastal seas. Our sampling efforts in 2018 and 2019 aimed to characterize the optical (absorption, backscatter, particle size distribution, remote sensing reflectance) and biogeochemical properties (POC, PN, phytoplankton pigments, suspended particulate matter (SPM), and nutrients), during high and low river discharge periods. Our results indicate that the Yukon River exports high levels of SPM with low carbon content to Norton Sound, while ANWR rivers export low levels of SPM with relatively higher carbon content to the Beaufort Sea. Furthermore, SPM levels in the Yukon delta of 550 mg m^-3 far exceed measured values at the upstream site (~300 mg m^-3) monitored by Arctic-GRO and USGS suggesting that resuspension and river/delta bank erosion in the delta area contributes to the particle load observed. Coastal erosion at the land-sea boundary along the Beaufort coast has been previously demonstrated to be a significant source of sediments and organic matter to the Beaufort Sea. Preliminary relationships of optical-to-biogeochemical properties of particles will be presented. These relationships will be used to parameterize satellite ocean color algorithms to derive properties of suspended particles for use in bi-decadal satellite data analysis to quantify changes in particle composition.