Amictic lakes are "perennially sealed off by ice, from most of the annual seasonal variations in temperature.
Amictic lakes occur in Arctic, Antarctic, and alpine regions and due to permanent ice-cover, these physical/thermal influences have a limited effect on circulation in the water column.
This melting occurs as a result of heat absorbed by water and sediments below the ice, particularly in the shallow-water areas, when snow does not cover the ice, and also by heat flow and meltwater runoff from the surrounding land.
Mixing below the ice occurs due to density currents generated by heat from direct solar radiation and from meltwater runoff which may differ in density from the lake water due to both temperature and suspended sediment content, depending on its source and flow path.
Despite these processes, the effects of wind at the lake surface are highly reduced due to the ice cover, and so vertical mixing of the water column may be incomplete.