Large rivers, key components of the land-ocean branch of the global water and biogeochemical cycles can have important impacts on physical, biological, optical, and chemical processes in coastal oceans. It is therefore important to routinely monitor the time-varying discharge patterns of river plumes. Sea surface salinity (SSS) is a critical observable for monitoring river plumes and studying their impacts. Satellite and in-situ SSS gridded products have been used to characterize the variability of some river plumes. However, their consistency has not been examined systematically for near major river mouths of the world’s oceans.

SSS data from different products are used in a recent study by Fournier and Lee (2021) for intercomparison at the mouth of the world’s ten largest rivers. In particular, data from the NASA Soil Moisture Active Passive (SMAP) and the ESA Soil Moisture Ocean Salinity (SMOS) satellite missions, as well as two widely-used in-situ products (one from Scripps Institution of Oceanography (SIO) and one from Japan Agency for Marine-Earth Science and Technology (JAMSTEC)) based on Argo, buoy and Conductivity-Temperature-Depth (CTD) in situ measurements are used.

The SMAP and SMOS satellites have excellent consistency in depicting seasonal-to-annual variations of SSS near the mouths of the ten largest rivers in low- to mid-latitude oceans. Two widely used in-situ products (SIO & JAMSTEC) underestimate these variations substantially due to the sparse in-situ sampling of the active river plumes following the high discharge season (figure above) despite the relatively good consistency between them. Based on this study it is recommended that caution be taken in using in-situ products like the ones in this study, as a benchmark to assess the accuracy of satellite SSS in river plume regions.