Changes in the Ice-Free Period in the Chukchi Sea Based on Remote Sensing and Coastal Observations

Over the past two decades, beginning in the late 20th century and early 21st century, the extent, age, and thickness of sea ice have undergone significant changes in the Arctic Ocean, clearly reflecting ongoing climate change. This study examines regional patterns of observed warm-season sea ice extent decline and changes in the duration of the ice-free period (IFP) in the Chukchi Sea. The study is based on passive microwave remote sensing data and coastal observations, supplemented by literature sources. The average annual sea ice extent for 2011–2024 period decreased by 12.6% compared to 1981–2010. The average monthly sea ice extent declined most rapidly in September, October, and August. Between 1979 and 2024, the Chukchi Sea experienced a nearly universal increase in IFP duration, driven by both an earlier onset of the IFP and a longer IFP. Coastal observation data from Roshydromet coastal stations were also compared with remote sensing data in the coastal zone of the Chukchi Sea. Satisfactory agreement in mean annual values and rates of change was found only for the IFP end dates. Furthermore, determining the IFP start and end dates using the 15% threshold method and the original modified threshold method, developed specifically for the accurate analysis of coastal satellite data, yielded identical results.