The Evolving Decline of Landfast Sea Ice in Northern Alaska and Adjacent Waters: Results from an Updated Climatology

Abstract We present a new 27‐year record of landfast sea ice extent in northern Alaska and adjacent waters, which uses ice chart data to extend a previous analysis based on synthetic aperture radar (SAR) imagery. This new climatology provides updated information on the decline of landfast ice in a region of the Arctic that has seen extensive losses of sea ice in recent summers. By comparing our results with early satellite data analysis from the 1970s, we find that trends in the timing of landfast ice have been ongoing for at least 50 years. Over the period 1996–2023, the landfast season shortened by 19 days/decade in the Chukchi Sea and 13 days/decade in the Beaufort Sea, primarily due to later formation of landfast ice. Also, the time between onset of freezing air temperatures and landfast ice formation is increasing, which is consistent with a coastal ocean that takes longer to freeze. While it was previously reported that the typical annual maximum width of landfast ice in the Chukchi Sea declined by 13 km between periods 1970–1976 and 1996–2008, we find this retreat has slowed with a decline of 3.3 km over the course of our data set as few areas of extensive landfast remain to be lost. Conversely, landfast sea ice extent in the Beaufort Sea had previously been found to have remained constant since the 1970s, but we find an average reduction of 2.5 km. We attribute this emergent phenomenon to a reduction in the number grounded ridges forming offshore.