Sea ice in the Arctic Ocean has decreased in extent, and multi-year ice is being replaced by first-year ice (eg, Stroeve et al., 2012; Meier et al., 2014; Lindsay and Schweiger, 2015; Kwok, 2018). Changes in sea ice conditions due to thinner, less extensive, and younger sea ice in the Arctic Ocean have had pronounced effects on ice dynamics (eg, ice deformation and ice drifting speed; Rampal et al., 2011; Spreen et al., 2011). Crack formation and the development of leads in sea ice are strongly related aspects of ice dynamics (Rampal et al., 2011; Spreen et al., 2011; Itkin et al., 2017). Sea ice lead formation affects the physical, chemical, and biological processes that take place at the interface between the ocean and atmosphere by allowing direct exchange between the two, unrestricted by sea ice (Maykut, 1978; Zemmelink et al., 2005; Petrich et al., 2007; Steiner et al., 2013; Loose et al., 2014; Assmy et al., 2017; Fransson et al., 2017; Nomura et al., 2018; Ólason et al., 2021; Silyakova et al., 2022). Lead width can vary from a few meters to many kilometers (eg, Wilchinsky et al., 2015). In wintertime, heat and moisture are supplied from the warm surface waters of a lead into the cold atmosphere, and new ice forms at the lead surface (Morison et al., 1992; Morison and McPhee, 1998). In addition, gases such as carbon dioxide and methane are actively exchanged between the lead surface and the atmosphere (Steiner et al., 2003; Fransson et al., 2017; Silyakova et al., 2022). In summertime, meltwater is supplied to the ocean (Eicken, 1994; Richter-Menge et al., 2001; Eicken et al., 2002; Smith et al., 2022), where it occupies the surface of leads during the melt season (Nansen, 1902; Perovich and Maykut, 1990; Richter-Menge et al., 2001; Zemmelink et al., 2005; Golovin and Ivanov, 2015; Nomura et al., 2018), and this less dense low-salinity water is kept at the surface. Meltwater in a lead is also derived from snow meltwater on sea ice that flows into the lead from the sea ice surface and bottom of sea ice (Golovin and Ivanov, 2015; Nomura et al., 2018; Smith et al., 2022). Therefore, during the melting season, leads accumulate meltwater supplied from both above and below the sea ice. The presence of meltwater creates a strongly stratified environment within leads (Richter-Menge et al., 2001; Golovin and Ivanov, 2015; Nomura et al., 2018) and can form a persistent layer at the surface that may prevent the exchange of heat and gas between seawater and the atmosphere. For a while after formation, leads can act as “windows” for the exchange of heat, gases, vapour and particles (aerosols) to the atmosphere (eg, Willis et al., 2018; Baccarini et al., 2020; Beck et al., 2021). However, during the melting season, this meltwater layer may reduce atmospheric exchange, because strong stratification restricts water exchange and the shallow meltwater layer equilibrates with the atmosphere, resulting in a small gradient for heat and gas flux between the lead surface and atmosphere. Despite this potential reduction in atmospheric exchange, high concentrations of dimethyl sulfide in the top surface of the meltwater layer (within 0.25 m) under these stratified conditions were observed in Weddell Sea leads (Zemmelink et al., 2005). This observation suggests that stable conditions within a lead and sunlight on the open lead surface enhance biological productivity (Nomura et al., 2018).

Such shallow stratification may weaken as a result of, eg, tidal mixing (Nomura et al., 2008), wind mixing (Inoue and Kikuchi, 2006), or ice movement during a high wind event (Richter-Menge et al., 2001). Golovin and Ivanov (2015) showed that lead water dynamics changed across seasonal …