Annual onset dates of six river flow and landfast ice interaction phases in the Lena Delta, 2000-2025

This dataset provides annual onset dates for six recurring phases of interaction between spring-summer river inflow and landfast sea ice in the Lena River Delta and adjacent Laptev Sea for 2000–2025. Phase 1 corresponds to the first isolated flooded ice patches, Phase 2 to the formation of a continuous flooded ice zone along the delta coastline, Phases 3 and 4 to the development of thaw holes in the eastern/southeastern and northern sectors, respectively, and Phases 5 and 6 to landfast ice break-up in the northern and eastern/southeastern sectors, respectively. Onset dates were identified by visual interpretation of available optical satellite images, including MODIS and VIIRS observations. Data are provided as ISO 8601 calendar dates in one record per year. Missing dates reflect insufficient or ambiguous interpretable observations and do not indicate absence of the physical process. A README provides the operational definitions, spatial context and important limitations.