the North Pole. During the Antarctic summers, most sea and uniform under-surfaces of newly-formed fast-ice,
ice breaks up, drifts northward and eventually melts. Con- through relatively flat areas with brine channels in first-
sequently, most Antarctic sea ice is first-year ice. year ice, to three-dimensional and often very complex
habitats in older, multi-year ice. In the Antarctic, most
Snow plays an important role in the formation and na- sea ice is first-year ice, but additional habitat diversity is
ture of sea ice in both polar regions, and changes in pat- provided by the small amounts of multi-year ice, exten-
terns of precipitation, both as snow and as rain, will have sive ice shelves, and anchor ice in coastal areas.
impacts on sea ice. Young ice without a snow cover thick-
ens faster than young ice with an insulating snow cover. Changes in these habitats will have many impacts on
Snow properties such as grain shapes and sizes influence ice-associated organisms. Impacts on one type of organ-
the snow’s albedo, and the extent and properties of snow ism in turn have impacts on other organisms through
are the dominating factors controlling how much energy the polar food webs (see box on sea ice and food webs).
in the form of solar radiation reaches the ice. Snow can Some of the consequences of changing sea ice habitat:
also contribute to the ice mass through transformation If multi-year ice disappears, long-lived amphipods and
into ice. Superimposed ice forms when mild weather the larger ice algae will decline drastically. If summer
melts snow at the surface, or when rain falls. Water per- pack ice disappears in the Arctic Ocean, the ice-associ-
colates downwards through the snow cover and reaches ated macrofauna as well as some of their predators will
the snow–ice transition zone where it is cold enough that likely vanish from Arctic drift ice.
the snow-water mixture freezes. Snow can also be added The Arctic system will change from ice-dominated to
to ice when seawater seeps into the snow–ice transition open-water, with enhanced production in the open wa-
through cracks in the ice or from the side of an ice floe, ter but weaker connections between the pelagic and
resulting in “snow ice”. the benthic systems, meaning less food for bottom-
dwelling organisms and their predators
37
.
Changes in wind strength and wind patterns would Reduction in ice thickness and extent in the Arctic
also affect many characteristics of sea ice. More wind or Ocean is expected to decrease the southward transport
more extreme wind events would lead to more ice rafting of ice-associated organisms on drifting ice, reducing
and ridging and increased ice thickness in some areas. prey availability and carbon input to subarctic seas.
Changes in winds would especially affect coastal areas. Changes in the timing of spring may also be impor-
Land-fast ice formation and evolution is highly depend- tant: earlier ice break-up and an earlier onset of the
ent on winds. Ice conditions in bays, fjords and sounds annual bloom in plankton may lead to a temporary
especially will be substantially different in a climate with mismatch between primary production (algae) and
different wind patterns than at present. secondary production (the animal life that feeds on the
algae) in some areas.
Marine biodiversity associated with sea ice and In the Antarctic, reductions in sea ice may be linked
implications for food webs to declines in krill populations, with cascading effects
on survival and reproduction of krill predators, such
Arctic and Antarctic sea ice provides habitats for a wide as penguins. However, the relationship between vari-
range of ice-associated organisms
36
. The diversity of life ations in krill stocks and sea-ice extent may be influ-
associated with sea ice is largely dependent on the type enced by long-term cyclical patterns as well as climate-
and age of the ice. Habitats range in complexity from flat induced trends
38–40
.
CHAPTER 5 ICE IN THE SEA 79