Geology Reference
In-Depth Information
serious cause. The disappearance of sea ice may contrib-
ute to this anomaly as well.
Normally, under ocean currents and wind, Arctic
sea ice moves southward from the Arctic Basin to the
Greenland Sea through Fram Strait (located between
Greenland in the west and Svalbard in the east). As it
continues its journey south and when the melt season
approaches, the sea ice starts to melt. Since sea ice is much
less salty than the surrounding seawater, the melt decreases
the salinity of the seawater near the surface, albeit at
another location from its initial formation. Excessive
melting of sea ice (or icebergs) may lead to a great salinity
anomaly. Therefore, any major change in Arctic winds
that move a considerably larger volume of sea ice through
the Fram Strait into the North Atlantic or any significant
increase in the temperature of the Nordic Seas are possi-
ble scenarios that may trigger this anomaly.
use the breathing holes for locating and getting their
kills for food as well as for the furs. Harp seals live
and give birth to their pups on heavy ice floes within ice‐
edge zones (Figure 1.10). In winter, Arctic foxes venture
onto the sea ice to scavenge for remains of seals killed by
polar bears.
As for the Antarctic, Weddell seals spend most of their
time beneath fast ice while coming onto the sea ice surface
only to rest and have their pups. Leopard and Crabeater
seals are species of deep pack ice. However, since Leopard
seals are predators and cannot move easily on sea ice,
the Crabeater seals often rest on rougher ice where they
are safe from predation. Emperor Penguins, found only in
the Antarctic, prefer the fast‐ice zones. In general, marine
biologists confirmed that animals prefer ridged ice (com-
pared to level ice) as an attractive habitat. From this dis-
cussion it is obvious that the ice information needed to
identify the suitable habitat for each species involves some
key surface features, not physical properties or crystalline
structure of the bulk ice. Remote sensing observations
that can be used to identify such features (e.g., fast ice,
ridges, leads, ice edge, etc.) are presented in Chapter 9.
At the bottom of the marine food chain many micro-
organisms find their habitats within the volume of the
sea ice. A notable review on this subject is presented in
Horner
[1985]. When seawater freezes, the salts are
entrapped within and between the ice crystals in the form
of brine, filling a network of “pockets” and “channels”
(section 2.3.1). Brine volume fraction can represent up to
30% of the ice volume (section 3.4). The diameter of the
brine pockets is usually less than 1 mm (Section 4.5.2).
Brine provides the necessary nutrients to host extensive
algal, phytoplankton (microalgae), and bacterial com-
munities. Ice algae contribute considerably to the total
1.4.6. Sea Ice in Marine Biology
Sea ice provides habitat, shelter, breeding, feeding,
nursery, and hunting grounds for a variety of species,
ranging from microorganisms (alga and bacteria) to
birds and marine mammals (polar bear, walrus, and a
few species of whales and ice‐associated seals). Sea ice
also supports the habitats of many different fish as it
maintains the seawater at a warm enough temperature
for their survival. A retreat of sea ice will decrease the
available platforms that birds and mammals use to rest
on and from which to hunt. There have been concerns
that this may lead to significant loss in the population of
those species. A dedicated chapter on sea ice as a critical
habitat for polar marine mammals and birds in presented
in the topic by
Thomas and Dieckmann
[2009]. The sur-
vival of the animal populations is related to the presence
of areas of ice‐free waters within sea ice cover. These
areas provide migration routes and sources of abundant
underice food reserve for animals. A notable example of
such areas is polynyas. These are areas within an exten-
sive ice cover that contain open water and thin ice even in
the middle of winter when atmospheric temperatures are
very low.
Animals that depend on sea ice for their survival prefer
different habitats within the ice cover. For example,
bearded seals and walruses prefer areas of thin or broken
ice cover in relatively shallow water because their main
food source is benthic invertebrates. Walruses and belugas
live along leads within pack ice. Ringed seals prefer fast
ice because of its stability for the successful rearing of
their pups and the sufficient snow cover for construction
of birth lairs. They usually congregate along the edges of
the ice and they use holes in the ice to breathe (Figure 1.9).
Polar bears also use this ice type since their main food is
ringed and bearded seals. Traditionally, Inuit hunters also
Figure 1.9
Seal breathing hole in first‐year fast ice in Lancaster
Sound, Canadian Arctic (photo by M. Shokr, unpublished).
