An Exceptionally Fresh Chukchi Sea in Summer 2024 Driven by Intense Precipitation and Late-season Sea Ice Melt

The Chukchi Sea is the gateway for Pacific-origin waters entering the Arctic Ocean, and freshwater variability of this inflow strongly influences Arctic stratification and circulation. During June–September 2024, hydrographic observations documented exceptionally fresh conditions throughout the Chukchi shelf relative to the historical observational record, corroborated by observations from local communities. Here, we investigate the causes of this freshening using in situ measurements, satellite sea ice concentration observations, atmospheric reanalysis, and a regional numerical model. Oxygen isotope (δ18O) data and satellite observations indicate that persistent sea ice along the Siberian coast contributed substantially to the freshwater anomaly, with sea ice meltwater comprising up to 15% of surface waters. Above-average precipitation and river discharge also enhanced meteoric freshwater inputs. Perturbation experiments using a downscaled regional configuration of the ECCO v5 alpha ocean state estimate demonstrate that precipitation from strong atmospheric cyclones during July–August enhanced coastal freshwater signals, while delayed melting of Siberian coastal sea ice sustained the extensive surface freshwater anomaly in the central Chukchi Sea into September. These results reveal a combined influence of remote sea ice anomalies and regional atmospheric forcing on Chukchi shelf hydrography, highlighting how evolving sea ice and atmospheric conditions may drive salinity variability and water mass distributions across Arctic shelf seas.