Assessing the Regional Accuracy of Arctic Satellite Sea Surface Salinity: Insights From Reanalyses and In Situ Observations

In the Arctic, Sea Surface Salinity (SSS) serves as a key tracer of freshwater variability and upper-ocean dynamics. While spaceborne SSS observations provide a unique capability for monitoring near-surface variability across undersampled polar regions, systematic quality assessments are essential to improve retrieval accuracy and ensure reliable interpretation. This study evaluates the spatio-temporal accuracy of five widely utilized satellite-derived products from the Soil Moisture and Ocean Salinity (SMOS), Aquarius, and Soil Moisture Active Passive (SMAP) missions across nine pan-Arctic regions through comparative analysis with in situ and model reanalysis data. While satellite and reanalysis products generally agreed on large scale September salinity patterns, major discrepancies emerged in river-influenced areas. Arctic-dedicated satellite products exhib ited stronger temporal correlations with model reanalysis (r up to 0.95) and greater spectral consistency relative to global datasets. However, salinity overestimation near ice margins and meltwater outputs persisted across most observational records–particularly during summer months–, highlighting the impact of meltwater stratification and unresolved contamination on SSS retrievals. Comparative analysis with in situ measurements showed that the CCI dataset demonstrated the closest agreement among the five SSS products in the Nordic Seas, with RMSD (R2) values ranging from 0.41 to 0.54 (0.21 to 0.69). Accurately capturing fresh water masses in the central Arctic remains a challenge (RMSD > 1.12), with BEC exhibiting smaller errors in most marginal seas but less variability on the eastern Arctic. These findings reinforce the added value of regionally-tailored satellite products in extending the utility and improving the accuracy of SSS monitoring in the Arctic Ocean.