3. Winter, Cold and Mature Sea Ice

This chapter describes a period of low air temperatures, darkness or very little light, cold ice, minimum brine volumes, and strongly reduced ice permeability. The first section provides an overview of the physical and optical conditions of this winter ice (3.1). Both snowfall and snowdrift are frequent during winter and an overview of the effects of a thick snow cover on sea ice is provided (3.2). Increased colonization of the sea ice bottom by bacteria and ice algae is initiated in late winter around first light, and an example is given (3.3). Once these microorganisms have colonized the ice the important growth limitations of bacteria and algae are considered (3.4), along with how they are able to adapt to these extreme conditions, and their seasonal species succession (3.5). The purposes of EPS and the functioning of different pigments found in ice algae are described (3.6). This is combined with a description of low light conditions and related photosynthesis (3.7), and exemplified with a case study from Station North, NE Greenland (3.8).