A Decade of Arctic SSS Variability from Satellite and Reanalysis Data

The Arctic system is transitioning into a new regime whose properties are yet to be determined, as several feedback processes are undergoing unprecedented changes. Accelerated loss of sea ice and glaciers, enhanced discharge from major pan‑Arctic rivers, widespread permafrost degradation, and a strengthening of the global hydrological cycle are collectively reshaping the upper ocean, making it warmer and increasingly fresh. Sea Surface Salinity (SSS), recognized as an Essential Ocean Variable, provides an integrated measure of atmosphere-ice-ocean coupling. This work investigates the spatial and temporal patterns of SSS and their short-term evolution across nine pan-Arctic regions of the over the satellite period 2011–2022, with a particular focus on how these changes relate to key drivers of surface freshening. To achieve this, we use three Arctic-dedicated satellite products –two from ESA’s Soil Moisture and Ocean Salinity (SMOS) mission, developed by the Barcelona Expert Centre (BEC) and the Laboratory of Ocean and Climatology Expertise Center (LOCEAN), along with the Climate Change Initiative Salinity (CCI) dataset– and GLORYS12v1 model reanalysis. The consistent agreement between satellite observations and model outputs in September –when Arctic coverage is at its annual maximum (r > 0.54) –highlights recent advances in salinity retrievals and their ability to capture key oceanographic processes. Throughout this month, the spatial SSS trend revealed a statistically significant freshening in the northern Barents Sea, with particularly low anomalies in 2019 and 2022. On the other hand, a basin‑wide freshening is evident in all regions except the Kara Sea, with the largest declines (~0.2 yr⁻¹) found near major Arctic river mouths, where a concurrent SST increase further highlights the influence of continental freshwater inputs. The seasonal analysis over the year‑round ice‑free regions (Nordic and Barents Seas) revealed pronounced winter discrepancies among all products –including against in situ data– and most notably in the Norwegian Sea, showing that the drivers of these differences are not yet fully understood. A significant summer freshening emerged along southeastern Greenland, largely shaped by the pronounced anomalies of 2017 and 2021. These shifts reflect the combined influence of variability in sea‑ice export, the timing of melt onset, and atmospheric circulation patterns that govern the delivery and redistribution of freshwater. Meanwhile, the highest summer SSS anomaly in the Barents Sea occurred near the ice edge in 2015, following a winter with exceptionally large sea‑ice volume anomalies. The northward winter transport of sea ice (> 0.18 km³ month⁻¹), enhanced by a positive Arctic Oscillation phase, displaced the ice edge northward, leaving the meltwater signature above 77.5º N. These results highlight the crucial role of remotely sensed SSS in providing insights into the Arctic Ocean's changing conditions and their global implications.