Satellite remote sensing of riverine freshwater contribution in Hudson Bay marine system

Freshwater regulates stratification in marine systems, a key driver of circulation, productivity, and exchange processes. This is especially important in the Arctic Ocean, where nearly one fifth of global freshwater drains, and an intensifying hydrological cycle increases freshwater input. However, Hudson Bay, an Arctic marginal sea that receives three times as much river runoff yield per unit area as the Arctic Ocean, remains one of the least observed components of the Arctic freshwater system. This thesis therefore develops satellite based approaches, supported by field data, to map seasonal distributions of river water (RW) and sea ice melt (SIM), the main freshwater sources in the Hudson Bay marine system. The third chapter examined the dispersion of the combined Nelson and Hayes River plume into southwestern Hudson Bay using satellite-derived chromophoric dissolved organic matter (CDOM) and total suspended solids (TSS). A new method showed that quantile concentrations of CDOM declined exponentially from the river mouth and varied with river discharge, whereas TSS did not, demonstrating CDOM as an effective river plume tracer. Wind forcing further regulated plume transport, with anticyclonic winds driving riverine CDOM towards central Hudson Bay and cyclonic winds promoting eastward alongshore transport. The fourth chapter used satellite-derived salinity and CDOM to map RW and SIM fractions in the surface waters of Hudson Bay and James Bay (HJB), based on RW, SIM, and seawater (SW) fractions derived from salinity–oxygen isotope ratios. Satellite retrievals reproduced known freshwater patterns, with RW dominating southern and eastern regions, particularly in James Bay, which receives the largest riverine inputs within the Hudson Bay marine system. Satellite retrieved SIM prevailed in central Hudson Bay and declined through summer. From 2011 to 2019, RW fractions increased while SIM fractions declined across HJB. Since RW and SIM are evolving in the surface waters of HJB, the fifth chapter determined which freshwater type controls stratification by analyzing salinity, temperature, and oxygen-isotope profiles. Results show that RW dominates stratification year-round, from coastal waters to northern HJB. Projected increases in wintertime RW discharge will likely enhance stratification and may impede deep-water renewal. Therefore, by combining satellite-based ocean color data, salinity, and isotope-based analyses, this thesis advances understanding of freshwater distribution, and stratification in the understudied Hudson Bay marine system.