Continental freshwater discharge influences sea surface salinity variability near world’s megadeltas

Sea surface salinity ([Formula: see text]) is a key parameter in the thermohaline circulation of global oceans. Near the megadeltas, inland streamflow through large catchments plays a crucial role in mediating salinity. While some regional studies have investigated how [Formula: see text] is impacted through water cycle and climate components, a global scale quantification of inland streamflow contribution on [Formula: see text] variability is lacking. Here, we utilized remote sensing and observation-driven datasets to quantify the statistical associations between [Formula: see text] and streamflow ([Formula: see text]) at 48 megadeltas worldwide. This study uncovers a robust negative association between [Formula: see text] and [Formula: see text], with correlation coefficients [Formula: see text] less than [Formula: see text] for seasonal data found in 26 of the 48 megadeltas, and less than [Formula: see text] for deseasoned data in 21 megadeltas. The anticorrelation relationship is more pronounced in large deltas, particularly near tropical climates and in river-influenced deltas. The study also underscores the significant roles of climate, morphological, and anthropogenic stratification in impacting the natural influence of freshwater discharge on <i>SSS</i>. By highlighting the interconnected impacts of alterations in terrestrial water cycle upstream and [Formula: see text], this work contributes to enhancing our understanding of global ocean and climate circulation patterns and in tackling environmental issues pertaining to marine ecosystems.