Arctic sea ice is retreating at a high rate, also due to the positive ice-albedo feedback loop: as ice melts and disappears, it reflects less sunlight, further accelerating ocean warming. One proposed way to slow the retreat is by thickening sea ice in winter, increasing its chances of surviving summer melt. This could be achieved by artificially flooding existing sea ice with seawater pumped from below, allowing it to freeze at the surface through exposure to cold air and thicken the ice layer. However, the effectiveness of this approach remains uncertain, as numerical models show contrasting results and few field experiments have been conducted. This study examines the growth and melt of ice through spring and summer after artificial flooding covering (Formula presented.), resulting in thickened (+26 cm) snow-covered first-year sea ice. Observations were carried out in Vallunden Lagoon (Van Mijenfjord), Svalbard, from 20 March to 24 June 2024, with flooding and intensive in situ measurements from 11–15 April. Artificial flooding significantly heated the upper two-thirds of the original 90 cm thick ice, increasing salinity. Surface albedo evolution was influenced by specific events such as slush formation, snow drift, and a major meltwater drainage event in spring. Artificial flooding resulted in thicker ice and delayed rotten ice formation by 6 days, but did not delay the disappearance of ice in summer compared to a non-flooded reference site. Experiments at other scales and locations could help reveal how local conditions and flooded area size influence results and the potential of this method.

A field campaign in the Vallunden lagoon in the Van Mijenfjorden on Spitsbergen was conducted to gather data on sea ice restoration by artificial flooding. Sea ice thickening was initiated by pumping sea water from below the first-year sea ice onto the surface without removing the covering snow layer. Part of the data was collected by four thermistor strings, two radiation sensors, and one anemometer. All measurement systems were left in the field until recovery of the floating systems in summer. Data provided by the measurement devices were received remotely to gather data before, during, and after the flooding phase (including the melting for as long as the sensors were sending data). Furthermore, coring systems were used to extract 88 ice cores for analysis of temperature, density and bulk salinity profiles along the full length of the ice cores before, during and within four days after flooding. The data set can be used to investigate physical processes involved in the ice growth before, during and after flooding. The data can be used to understand the development, growth and melting of snow ice. The radiation data can be used to analyze the (reflected) radiation of the initial, flooded and melting ice. Data gathered during the melting can be used to investigate the melting of thickened sea ice with different initial conditions prior to the onset of melting. Data on bulk salinity can be used to investigate short-term salt migration. Combing the different insights, growth- and melting models of sea ice including snow and snow ice can be validated. The understanding of melt-water drainage events could be improved and flow models for simulation of artificial flooding of snow-covered first-year sea ice could be further developed using the data.