A lead (/ˈliːd/, rhymes with "reed") is a large fracture within an expanse of sea ice, defining a linear area of open water that can be used for navigation purposes.
Additionally it has been lately found that ice leads contribute significantly to the amount of mercury deposited onto surface and leaked into the ocean.
[6] Unlike polynyas, which tend to occur, and remain, at a given location, leads are transient features that can form anywhere in an ice-covered ocean.
Leads are cracks or fissures that initiate inside an otherwise continuous sea ice cover, and open up progressively afterward.
[6] Because leads are associated with the initial break up of an ice cover, they open the way to various dynamic processes that can take place afterward, involving the interaction between individual floes, such as the formation of pressure ridges.
[6] In windier regions, as in the Southern Ocean, frazil ice accumulation may occur along the downwind side of leads.