Geology Reference
In-Depth Information
activities in these areas. No doubt, the Arctic waters, par-
ticularly the legendary Northwest Passage that passes
through the Canadian Arctic Archipelago and the
Beaufort Sea, will be used more in the future for shipping
goods between Asia, North America, and Europe.
Average sea ice covered area in either the Arctic or the
Antarctic is about the same (about 15 million km
2
) during
the winter. However, because the mean thickness of sea
ice is 3 and 1.5 m in the Arctic and the Antarctic, respec-
tively, the maximum volume of the sea ice cover in the
Arctic (about 0.045 million km
3
) is nearly twice that of
the Antarctic. In summer, ice extent shrinks significantly
to about 50% of the winter coverage in the Arctic. Nearly
90% of the sea ice coverage disappears by the end of the
summer in the Antarctic. Ice that melts completely dur-
ing the summer is called “seasonal ice” or “annual ice.” If
the ice melts only partially, then the part that survives
until the next winter and growth season is called “peren-
nial ice.” This can be second‐year or multiyear ice depend-
ing on how many summers the ice has survived.
As a major component of the cryosphere, sea ice influ-
ences the global ocean and atmosphere in a profound
manner. Its continuous interaction with the underlying
oceans and the overlaying atmosphere leaves major
impacts on weather, climate, and ocean current systems.
Moreover, ice in one form or the other plays a significant
role in the daily life of communities inhabiting the cold
regions of Earth. Sea ice in particular influences the
coastal areas in most of the circumpolar nations of the
Northern Hemisphere. It affects to a lesser extent a few
countries in the Southern Hemisphere. Of all the coun-
tries of the world, Canada has the longest coastline and
has the largest reservoir of freshwater lakes and rivers
with floating ice in them annually at least for half of the
year. Except for Alaska, practically all the areas north of
the 49°N in North America belong to Canada. While sea
ice plays a major role in areas above 60° (north or south)
it does not affect areas below that latitude except in the
Hudson Bay, Labrador Sea, and the Gulf of St. Lawrence
in Canada and to a relatively lesser extent in the Baltic
Sea, Gulfs of Bothnia and Fin in Europe, the Sea of
Okhotsk, north of Japan, and Bohai Bay in China. Above
about 35°N in Eurasia and North America, most of the
streams, rivers, and lakes (Black Sea, Sea of Azo, and
Caspean Sea in Eurasia and the Great Lakes, to name a
few among thousands, in North America) have some ice
cover each winter. In fact, severity of winters in North
America is often measured in terms of ice coverage of the
five Great Lakes (Lake Superior, Lake Michigan, Lake
Huron, Lake Erie, and Lake Ontario).
In spite of the fact that sea ice covers vast areas of sea
surface of Earth, most of the people of the primary cry-
ospheric regions of the world have not seen it or are even
aware of it. That is because most people, even within the
cold regions of Earth, live far from the areas affected by
sea ice. Other than a few thousand multinational scien-
tific observers and a few annual visitors, nobody lives in
the south polar zone (beyond the Antarctic Circle). Only
a few small communities of the Falkland Islands and
Argentina consider the Antarctic region their home. On
the other hand, beyond the Arctic Circle in circumpolar
areas of Alaska, Canada, Norway, and Russia, perhaps a
few million people live. This is incomparable to the nearly
1500 million people living in Afghanistan, Bangladesh,
China, India, Nepal, Pakistan, and Tibet who are indi-
rectly affected by the Himalayan cryosphere, but sea ice
does not exists in that region.
It is not uncommon for people who live away from the
circumpolar boundaries to be confused between sea ice
and icebergs. Yet, general awareness about sea ice has
been growing as public information about the decline of
sea ice in the Arctic with its positive economic impacts
and negative environmental impacts is spreading. This
topic, though not oriented to serve as a popular science
document, provides scientific information with explana-
tions that may hopefully expand the domain of interest in
sea ice and attract a number of young scientists to pursue
studies about its physical aspects as well as its detection
using spaceborne remote sensing technologies.
The Arctic basin consists of primarily the Canadian
and the Eurasian subbasins [for details on these two
basins, see Chapter 3 in
Weeks
, 2010]. It is extremely dif-
ficult to obtain sea ice data in these areas because of the
remote locations and extreme climate conditions in which
ice exists. This situation also applies, perhaps to a lesser
extent to ice‐rich areas north of Russia because of year‐
round marine activities in Barents Sea, Kara Sea, Laptev
Sea, and East Siberian Sea. Until the beginning of the
twentieth century information about sea ice was mainly
gathered and used by the local people who lived in the
sub‐Arctic regions. Later, increasing information was
obtained from ship sighting and harbor icing records, but
the purpose remained to assist the very limited marine
operations. However, since the end of World War II in
1945 and the beginning of the Cold War, there had been a
significant increase in human activity in both the polar
regions and in particular the Arctic. Numerous weather
stations equipped to gather scientific information and
military bases with airports and radar lines were con-
structed in Canada, Alaska, and Greenland. Although
some of the supplies for the construction and mainte-
nance of these bases were transported by aircraft, ice‐
strengthened ships escorted by icebreakers were extensively
used during the summer melt season. Submarines and
buoys have also been used to gather data for sea ice in the
Arctic Ocean.
Although Russia has a longer history of record on
measurements of sea ice, dating back several centuries,
