Winter open-water zone remote sensing (2017-2023) and field (2023) data from the Yukon and Kuskokwim rivers and their tributaries in western Alaska

Timing and completeness of freeze-up on northern rivers impacts safe winter travel and may indicate responses to climate change. Open-water zones (OWZs) within ice-covered rivers are hazardous partly because their unpredictability and are suggested to be increasing in extent and persistence due to groundwater upwelling, higher winter discharge, and permafrost degradation. To better understand the distribution, variability, and mechanisms of winter OWZs, we selected nine study reaches totaling 400 kilometers (km) of the Yukon and Kuskokwim rivers and their tributaries for remote sensing analysis and field studies in western Alaska, USA. We identified 51 OWZs from late November optical imagery along these reaches ranging from 60 meters (m) to 9 km in length, inventoried their persistence over six years, and at a subset measured ice thickness, under-ice water depth and velocity, water-column and river-bed physico-chemistry. Concurrently, we investigated if and to what extent sediment was entrained in river ice at these same sites. These locations corresponding to observed OWZs were quantified by size, classified by hydrogeomophic location, and tracked for consistency during the preceding five years in the early (late November) and late (late February or early March) winter periods. A subset of these OWZ were visited in March of 2023 to collect additional field data on snow, ice, and physico-chemistry including ice sediment concentration. This research is part of the Fresh Eyes on Ice and Sediment Ice Learning on the Tanana (SILT) projects.