Abstract Freshwater dispersal controls stratification, circulation, and biogeochemical processes in Hudson and James Bay (HJB); however, limited field observations hinder understanding of how different freshwater types drive change. This study uses Aqua‐Moderate Resolution Imaging Spectroradiometer and Soil Moisture and Ocean Salinity‐Microwave Imaging Radiometer using Aperture Synthesis data to distinguish and map river water (RW) and sea ice melt (SIM), the main freshwater types in HJB. Satellite‐derived RW and SIM agree with in situ tracers, filling field data gaps that support future freshwater research. Higher RW fractions up to 0.40 in southern HJB and a seasonal SIM decline from 0.35 to 0.00 in central HJB match observed patterns. RW spreads offshore in July, contracts in August, and forms a coastal band in September, sustained by cyclonic winds despite reduced discharge. From 2011 to 2019, RW fractions increased (0.0048 yr −1 ) while SIM fractions declined (−0.003 yr −1 ) across HJB.
Basu et al. (Sat,) studied this question.