Sea ice leads play a significant role in the atmosphere–sea ice–ocean systems. Model representation of leads of varying widths is desirable to enhance our understanding of the behavior of leads and associated processes. We have developed a lead width distribution (LWD) conservation equation to explicitly simulate the evolution of leads of varying widths. The equation considers changes in leads due to ice advection, thermodynamic growth, lateral melting, and mechanical redistribution of lead width because of lead creation and ice ridging and fragmentation. The LWD is implemented into the Pan-arctic Ice-Ocean Modeling and Assimilation System (PIOMAS) to obtain insights into the large-scale changes in Arctic LWD over 1980–2022. PIOMAS results, validated by ICESat-2 lead observations, show that, over the leads with widths of 0.1–812 m, the simulated lead number distribution follows a power law, as indicated by satellite and airborne observations. Mean lead width and the number of leads increase in summer and decrease in winter. The simulated power-law exponent is higher in the ice pack interior, whereas the mean lead width and lead numbers are higher in the marginal ice zone. The exponent is decreasing, with more medium-width leads, and the mean lead width and lead numbers are increasing, mainly in warm seasons, over 1980–2022 with declining Arctic sea ice. Model experiments indicate that changes in surface sensible heat flux arising from a prognostic representation of LWD result in increased sea ice thickness and area because of increased surface heat loss.

Solar radiation is the key energy input to the ocean. In the Arctic Ocean and its peripheral seas, the distribution of solar radiation is strongly modulated by the presence of sea ice. In this study, we combined satellite and model products to investigate solar radiation partitioning between reflection to the atmosphere, absorption in the ice, and transmission to the ocean over 1984–2024. We present total annual solar heat partitioning, relative contributions to energy deposition from ice and open water, and trends in large-scale partitioning. The Arctic exhibited a decreasing trend in albedo (0.019 decade^-1) due to decreasing sea ice areal coverage and thickness. Consequently, solar transmittance into the ocean increased by 0.031 decade^-1, resulting in an additional ~300 MJ m^-2 of heat input over 1984–2024. A brighter, warmer ocean contributes to Arctic Amplification and may alter the functioning of the Arctic marine ecosystem.

The effect of leads in Arctic sea ice on clouds is a potentially important climate feedback. We use observations of clouds and leads from the Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) to study the effects of leads on clouds. Both leads and clouds are strongly forced by synoptic weather conditions, with more clouds over both leads and sea ice at lower sea level pressure. Contrary to previous studies, we find the overall lead effect on low-level cloud cover is –0.02, a weak cloud dissipating effect in cold months, after the synoptic forcing influence is removed. This is due to compensating contributions from the cloud dissipating effect by newly frozen leads under high pressure systems and the cloud enhancing effect by newly open leads under low pressure system. The lack of proper representation of lead effect on clouds in current climate models and reanalyses may impact their performance in winter months, such as in sea ice growth and Arctic cyclone development.