Although there are numerous glaciers in Canada, relatively few reach the sea and produce icebergs. All of these regions also produce icebergs. Icebergs calved into the Siberian seas may affect shipping along the Northern Sea Route. Because glacier ice accumulates atmospheric pollutants deposited on the glacier surface, there are also concerns that icebergs may represent a source of contaminants to the surface waters. The depth of permafrost depends on such conditions as climate, vegetation, and whether or not it was covered recently by glaciers or sea ice.
Some permafrost does occur in marine sediments.
Very deep permafrost is often a relict feature formed in unglaciated areas during the last glacial maximum. IFurther south, permafrost thins and becomes discontinuous, before disappearing entirely in warmer climate areas. Typically, a shallow upper zone of permafrost thaws in summer. This zone is called the active layer. Because the frozen ground underneath inhibits groundwater drainage, pollutants deposited on the soil surface do not disperse as readily as in temperate regions.