Impact of meteorological and oceanographic conditions on the state of sea ice in Hornsund, Svalbard over 23 years

Abstract. The full archive of historical SAR imagery at ~50 m resolution (Envisat ASAR, RADARSAT-2 and Sentinel-1) capturing the Hornsund fjord, Svalbard was used to create an unprecedented set of near-daily binary ice/open water maps over the fjord area for 23 seasons (2002–2025). We observe a general trend with the sea ice season shortening by 2.3 days yr⁻¹, and a gradual decrease in average ice coverage, particularly in the main basin of Hornsund (−1.6 % yr⁻¹). The interannual ice condition variability was strongly related to the autumn (October–December) and/or winter (January–March) air temperatures. The length of the sea ice season was shortened by 19.5 days for every 1 °C increase in mean autumn air temperature (R² = 0.61, p < 0.05). Air temperature remained under the freezing point for over 90 days before landfast ice freeze-up. Drift ice was present in the fjord before the freeze-up with an average coverage exceeding 20 % 40 days and 26 % one day before the landfast ice onset. The landfast ice season break-up period was characterised by a lack of drift ice, and positive air temperatures for over a month. The day of landfast ice freeze-up and break-up overlapped with an average sea ice thickness of 0.33 m and 0.57 m as derived from thermodynamic terms, respectively, suggesting the importance of other processes.