Geoscience Reference
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suspension feeders, supported by food delivered in strong near-bottom currents.
The other consists mainly of fauna living in the soft sediments and mobile epifauna
living at the sediment surface in areas receiving high amounts of phytodetritus
from the water column. However, these represent two extremes of a continuum,
and intermediates also exist. Many benthic organisms living on the Antarctic
continental shelf are characterised by gigantism, late maturity and longevity.
While Southern Ocean deep-sea animals usually do not tend to display gigantism,
we do not know to date whether late maturity and longevity apply for slope and
deep-sea animals.
Unlike terrestrial or pelagic ecosystems, the benthos depends on energy input
from the surface or the water column. Due to the variety of habitats available and the
bottom topography, benthic communities are complex, very diverse and their
trophic structures and the biogeochemical exchange between pelagic and benthic
ecosystems are largely unknown for most areas. Two immediately striking features
of this benthic diversity are that it is often extremely high
some groups such as
pycnogonids being more diverse within the Antarctic/Southern Ocean than
anywhere else globally
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and it is very largely restricted to the Southern Ocean
(endemic). The biomass and richness of some benthic communities is also often
extremely high, in global terms second only to that of tropical coral reefs.
Over global geological timescales, plate tectonics, palaeoceanography and the
resulting global climate changes (e.g. from greenhouse to icehouse) have had a
strong impact on the Antarctic marine fauna and
-
flora, including triggering the
evolutionary radiation of many Antarctic benthic marine species. These have
included events such as the progressive migration north of formerly cosmopolitan
taxa established during the Jurassic and Cretaceous periods when Antarctica was still
under greenhouse conditions, the creation of disjunct distributions due to plate
tectonics (for instance, during the disintegration of Gondwana), the active
migration of taxa in and out of the Southern Ocean and radiation events due to
the emergence of new adaptive zones and habitats after the climate changed.
Palaeoclimatic changes are thought to have driven latitudinal range shifts for
many taxa, serving as
into other regions.
As Antarctica is a large continent, the ocean and benthos surrounding it is
actually not at such a high latitude as much of the Antarctic terrestrial biome, or the
Arctic Ocean. The most southerly point in the ocean is found at 79
S (under a
permanent ice shelf) in the Weddell Sea, still more than 2000 km from the South
Pole. The continent
'
taxonomic diversity pumps
'
s fringing sea ice, isolated by the ACC, generates cold and highly
saline Antarctic Bottom Water, which is an important driver of global ocean
circulation. The linked isolation of Antarctica
'
is benthic faunas is due to temperature
decreases in the Southern Ocean in the Cretaceous period, when many species
became extinct while others displayed subsequent diversi
'
cation. A few survivors,
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