Kristina Prokopyeva: Interaction of Lena River Runoff with Landfast Ice in the Estuary

Kristina Prokopyeva’s talk focused on the interaction of spring runoff from the Lena River with river ice and landfast ice in the delta and estuarine nearshore zone. The work is motivated by the difficulty of observing the transition zone between the delta and the sea: hydrological measurements in the channels are constrained by ice and shallow water, and direct field observations during the spring flood are often impractical. The study therefore relies primarily on satellite imagery, which makes it possible to trace how river water emerges onto the ice, forms turbid plumes, and gradually changes the state of the landfast ice.

The central part of the seminar examined a sequence of phases that recurs from year to year. In late May, small water spots and meltwater ponds first appear on the ice; later they merge into larger fields of water. As the flood wave advances, river ice in the channels breaks up, openings form in the eastern and northern sectors of the nearshore zone, and eventually the landfast ice breaks, allowing the river plume to enter the Laptev Sea more directly. Participants discussed why openings form not only along the channels, how ice plugs affect the process, and which aspects can or cannot be quantified from optical satellite data.

Another part of the talk addressed 2000-2025 time series and forecasting of ice events. Kristina showed that several phases display statistically significant shifts toward earlier dates, while the earliest signs of water emerging onto the ice do not show the same trend. The discussion considered possible causes: Lena River water temperature, air temperature, the radiation balance, landfast-ice thickness and structure, and the possibility of fresh water freezing on top of the ice. For forecasting the timing of landfast-ice breakup, the study considered satellite indicators of the second phase together with hydrological data from the Tabaga, Zhigansk, and Kyusur stations; combining these predictors can refine the forecast as the flood wave moves downstream.

The seminar concluded by comparing the presented work with earlier studies of river-runoff and sea-ice interaction in Arctic deltas. Participants noted that individual elements of the process had been described before, but a systematic view of the full sequence of phases over 25 years of satellite observations provides a more complete picture. The practical value of this work lies in planning navigation, field campaigns, and supply operations near Tiksi and the Lena Delta, where even a few days of uncertainty in ice-breakup timing can be important.