Geoscience Reference
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the atmosphere. In contrast, large areas of the northern continents and archipelagos,
and, increasingly, the surface of the Arctic Ocean, become ice free for several months
during summer, enabling the absorption of solar radiation and leading to
temperatures several degrees higher on average than at comparable Antarctic
latitudes, suf
cient to support considerable biological productivity.
The Antarctic marine environment also faces environmental extremes. As well as
being one of the coldest, it is also one of the most thermally stable marine habitats on
the planet, and faces considerable disturbance from various forms of ice. As the
surface layer of two-thirds of the Southern Ocean freezes during the winter, the
'
of the southern hemisphere covered by ice can be doubled. The extreme
seasonality of the solar regime that underlies this also has the biological consequence
of generating short pulses of primary productivity during the summer months, and
therefore intense seasonality of food supply is an important challenge faced by
consumers. Sea ice and anchor ice formation in shallow water directly impact
benthic and littoral/intertidal habitats, though this typically only in
area
'
rst
few metres of depth. However, glaciers and ice shelves calving directly into the sea
generate icebergs of widely varying size and depth, whose movement can cause
considerable damage and destruction to benthic habitats, frequently to depths of
tens or hundreds of metres, and occasionally to more than 1000m.
Even without taking the extent of winter sea ice into account, the continent of
Antarctica is larger in area than the United States, Australia or Western Europe. It
would be extremely simplistic to think that it can be treated as a single entity in
biological terms. In describing how organisms have managed to make a success of
life in this distant and apparently hostile region, we have started with an initial
division into three distinct environments
uences the
-
the marine pelagic and benthic
ecosystems and the terrestrial ecosystem
recognising, however, that there are many
cross-cutting themes and linkages that provide some of the most exciting of
contemporary research
-
fields.
Life in the pelagic zone
The pelagic zone of all oceans is, in terms of volume, the largest ecological zone
(biome) on the planet, reaching from the water
s surface to the ocean depths and
extending from the coastal zones of all the continents. It is in the upper reaches of
this zone where sunlight stimulates growth in the unicellular plants, the
phytoplankton, and this starts the food chains that eventually lead to the seabirds,
whales,
'
fish and to humans. Sunlight only reaches into the top 200m or so of the
ocean and, below this productive layer can lie several kilometres of ocean that, other
than some exceptional communities based on chemosynthetic processes, is
dependent on what sinks or swims out of the surface layer to support the food webs
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