Geoscience Reference
In-Depth Information
yet they are critical to ecosystem function and resilience. In the marine environment,
the greatest risks are probably posed by the release of ballast water and the transfer
of organisms attached to the hulls of ships. Now tour ships spend half a year in
the Arctic and then 6months in the Antarctic, increasing the risk of transferring
species between the polar regions. Irreversible changes in the ecosystems of many
sub-Antarctic islands have already occurred, e.g. through the introduction of rats
and rabbits.
Albatrosses are regarded by many as iconic species and thus of cultural value,
but their numbers are in serious decline. One of the impacts of long-line
fishing is
the incident mortality of birds (by-catch). Typically a long liner deploys ~10000
baited hooks during a single long-line haul. This attracts birds, such as albatrosses
and petrels, and over the years thousands of birds have been caught and drowned.
Conservationists and scientists have been working with the
fishing industry to
reduce the deaths. Measures include having streamers behind the
fishing boats to
prevent birds getting close to the hooks before they sink out of range of the birds
'
diving capabilities. These measures have meant that the by-catch of birds in the
South Georgia area fell from ~6000 per annum in the late 1990s to none in 2006
and subsequent years. Alas, albatrosses are still on the decline; currently at the rate of
4% per annum for the wandering albatrosses. Research shows that birds are breeding
just as successfully as previously, but the returns of birds to breed are falling.
New tracking technology allows scientists to show that albatrosses often go to South
American and South African waters to feed; in these locations the same by-catch
mitigation measures have not been fully implemented.
Bi-polar comparisons and contrasts
The two polar regions have similarities. Both are much colder than the global
average, largely covered by snow and ice, and contribute signi
cantly to driving the
large-scale ocean circulation. Both the Arctic and the Antarctic Peninsula have
warmed at a rate about
five times the global average over the last half-century.
The icecaps on Greenland and the Antarctic Peninsula are both melting at lower
altitudes as a result of there being many more days when the air temperature is
above 0
C. Also sea ice trends in the Arctic are becoming more like that of
Antarctica each year, i.e. dominated by sea ice that melts every summer with only a
small area of multi-year ice.
There are many more differences than similarities between the poles and
these contrasts can act as excellent tests for geophysical and biological models
that have been developed in one hemisphere. Some of the differences include the
geography. Antarctica is essentially land surrounded by ocean, whereas the Arctic is
the converse but with substantial mountain chains at sub-Arctic latitudes. The
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