Geoscience Reference
In-Depth Information
Niño
La Niña climate oscillation. About 1 year following an El Niño event
(warm water in the eastern Paci
-
c), there is a reduction in the sea ice concentration
around the Antarctic Peninsula and the over-wintering krill population. This
impacts the food supply for the birds and seals the following summer around South
Georgia. Thus a physical change near the equator in one ocean basin causes a major
impact on the breeding success of animals and birds in the sub-Antarctic of a
different ocean basin 2 years later. This large spatial and temporal displacement is
a powerful illustration of how attribution of cause to effect can be very dif
cult in
climate change studies.
Sea ice changes are also cited as the explanation for the alternation in the
balance of the penguin population on Anvers Island on the Antarctic Peninsula.
Since 1975, the numbers of the Adélie penguin, which has a preference for sea ice
habitats, have fallen by a factor of eight from an initial population of about 16 000
birds. Gentoo and chinstrap penguins, that prefer open waters, have increased by
a similar factor but from a much lower baseline
gure. Hence there has been an
overall reduction in pygoscelid penguins.
Sea ice is also critical in the life cycle of emperor penguins. It is now possible
to identify their colonies from guano stains on the ice, and count individual birds
using high resolution, multispectral imagery from space. These studies have
found 10 previously unidenti
ed colonies and one known colony has disappeared
from the region where there have been large reductions in sea ice extent. The
population of emperor penguins is calculated from the satellite data to be about
600 000 birds, about 60% higher than previous estimates.
So climate change, especially through the impacts on sea ice, is having a major
impact on the top predators both through changes to the physical environment and
to their food chain. Much less is known about changes of the lower trophic levels.
The terrestrial environment
As less than 1% of Antarctica is ice free, the range of terrestrial habitats is very
limited indeed. Despite the small area, the logistic dif
culties of reaching many
exposed terrains means that Antarctica is poorly surveyed biologically and thus the
patterns of dispersal are not well established. There is little species overlap between
maritime and continental Antarctica in springtails, mites and nematodes and
therefore unexpectedly high local endemism. Combined biogeographical, molecular,
palaeological and geological studies are now all suggesting that much of the
evolutionary separation events occurred tens of millions of years ago. This is an
unexpected result. Glaciological modelling studies suggest that all the terrestrial
environments, except for the Dry Valley region, were over-ridden at glacial maxima,
and thus all terrestrial biology should have been very recent (i.e. since the last ice
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