February
25, 2007
ANTARCTIC
MARINE EXPLORERS REVEAL FIRST
HINTS OF BIOLOGICAL CHANGE
AFTER COLLAPSE OF POLAR ICE SHELVES
Once
roofed by ice for millennia, a 10,000 square km portion
of the Antarctic seabed represents a true frontier, one of
Earth’s most
pristine marine ecosystems, made suddenly accessible to exploration by
the
collapse of the Larsen A and B ice shelves, 12 and five years ago
respectively.
Now it has yielded secrets to some 52 marine explorers who accomplished
the
seabed’s first comprehensive biological survey during a
10-week expedition
aboard the German research vessel Polarstern.
While
their families at home in 14 countries were enjoying
New Year’s dinners, experts on the powerful icebreaking
research ship were
logging finds from icy waters as deep as 850 meters off the Antarctic Peninsula –
an area rapidly changing in fundamental ways. The
recent report of the Intergovernmental Panel on Climate Change shows
nowhere on
Earth warming more quickly than this corner of Antarctica, a
continent
1.5 times the size of continental United States.
The
expedition forms part of the Census of Antarctic Marine
Life (CAML), which has 13 upcoming voyages scheduled during
International Polar
Year, to be launched in Paris
March 1. A project of the global Census of Marine Life collaboration,
CAML is
responsible for the synthesis of taxonomic data and supports the
efforts of
national programs the world over.
Says
CAML leader Michael Stoddart of Australia:
“What we learned from
the Polarstern expedition is the tip of an iceberg, so to speak.
Insights from
this and CAML’s upcoming
International Polar
Year voyages will shed light on how
climate variations affect ice-affiliated species living in this
region.”
Leaving
South Africa
Nov. 23, the research icebreaker Polarstern operated by the Alfred
Wegener
Institute for Polar and Marine Research criss-crossed the northwest Weddell Sea. The cruise included
the Larsen A and B
zones, an area about the size of Jamaica
(or half the size of New Jersey,
a third the
size of Belgium).
The voyage ended Jan. 30.
With
sophisticated sampling and observation gear, including
a camera-equipped, remotely operated vehicle, experts on the Polarstern
have
returned with revealing photography of life on a seabed uncapped by the
disintegration of Larsen A and B. The expedition uncovered a wealth of
new
insights and brilliant images of unfamiliar creatures among an
estimated 1,000
species collected, several of which may prove new to science.
The
Polarstern’s mission included charting the environmental
impact of history’s largest known ice shelf collapses.
Polarstern’s team set
out to find what indigenous forms of marine life existed under Larsen A
and B,
and what new organisms now are opportunistically moving in, redefining
the
ecosystem.
“The
breakup of these ice shelves opened up huge, near
pristine portions of the ocean floor, sealed off from above for at
least 5,000
years, and possibly up to 12,000 years in the case of Larsen
B,” says Julian
Gutt, a marine ecologist at Germany’s Alfred Wegener
Institute for Polar and
Marine Research and chief scientist on the Polarstern expedition.
“The
collapse of the Larsen shelves may tell us about
impacts of climate-induced changes on marine biodiversity and the
functioning
of the ecosystem. Until now, scientists have glimpsed life under Antarctica’s ice
shelves only through drill holes. We
were in the unique position to sample wherever we wanted in a marine
ecosystem
considered one of the least disturbed by humankind anywhere on the
planet.”
“This
knowledge of biodiversity is fundamental to
understanding ecosystem functioning,” he adds. “The
results of our efforts will
advance our ability to predict the future of our biosphere in a
changing
environment.”
When
Antarctic glaciers reach the coast of the continent,
they begin to float and become ice shelves, from which icebergs calve.
Since
1974, a total of 13,500 square kilometers of ice shelves have
disintegrated in
the Antarctic Peninsula,
a phenomenon linked
to regional temperature increases in the past 50 years. Growing numbers
of
scientists worry that similar break-ups in other areas could lead to
increases
in ice flow and cause sea levels to rise.
Polarstern
Discoveries and
Insights
Larsen
zone seafloor sediments were extremely varied,
ranging from bedrock to pure mud. As a result, animals living on the
sediment
(epifauna) were highly varied as well, though far less abundant in the
Larsen A
and B areas – perhaps only 1 percent of animal abundance
compared to sea beds
in the eastern part of the Weddell
Sea.
In
the relatively shallow waters of the Larsen zone,
scientists were intrigued to find abundant deep sea lilies (members of
a group
called crinoids) and their relatives, sea cucumbers and sea urchins.
These
species are more commonly found around 2,000 meters or
so, able to adapt to life where resources far more scarce –
conditions similar
to those under an ice shelf.
Apparent newcomers
found colonizing the Larsen zone include
fast-growing, gelatinous sea squirts. The scientists found dense
patches of sea
squirts and say they were likely able to colonize the Larsen B area
only after
ice shelf broke in 2002.
Very
slow-growing animals called glass sponges were
discovered, with greatest densities in the Larsen A area, where life
forms have
had seven more years to re-colonize than Larsen B. The high number of
juvenile
forms of glass sponges observed probably indicates shifting species
composition
and abundance in the past 12 years.
Biodiversity in the Antarctic Peninsula
Among
many hundreds of animal specimens collected on the
voyage:
• 15
potential new amphipod (shrimp-like) species from 400
specimens. The star attraction is one of Antarctica’s
biggest-ever amphipod crustaceans – nearly 10 cm long, larger
than many similar
species found in temperate climates; and
• Four
presumed new species of cnidarians (organisms related
to coral, jelly fish and sea anemones). One is a
potentially new sea anemone, co-existing
on the back of a snail – their
symbiotic relationship providing locomotion for one
and protection for the other.
Extensive
analyses will be conducted to prove whether or not
candidate specimens are in fact new species. Confirmed new species will
be
logged in the Census of Marine Life OBIS (Ocean Biogeographic
Information
System) database and its Antarctic component SCAR-MarBIN (the Marine
Biodiversity Information Network), which to date has recorded some
5,957 marine
life forms, with an estimated 5,000 to 11,000 species yet to be
discovered.
The
remotely operated vehicle (ROV) used on Polarstern
revealed less scouring damage than anticipated from icebergs that broke
away
from the Larsen shelves. In shallower depths to about 220 meters, the
scientists found considerable richness of species variety.
“Iceberg
disturbance was much more obvious north of the
Larsen A and B areas where icebergs more typically run
aground,” says Dr. Gutt.
“In those outer areas, at depths of roughly 100 meters, we
observed fresh ice
scour marks everywhere and early stages of marine life recolonization
but no
mature community. At around 200 meters depth we discovered a mosaic of
life in
different stages of re-colonization.”
Extreme
Clamdigging
A
potentially far-reaching find by the Polarstern ROV: small
clusters of dead clamshells littering an area on the dark ocean floor
and
pointing to the presence of a very rare “cold seep”
– essentially a sea floor
vent spewing methane and sulphide. Seeps can create a temporary habitat
for
animal life in otherwise barren, inhospitable terrain for many years
before
extinguishing, abruptly starving off the community.
The
first-ever cold vent on Antarctica’s continental shelf
was discovered at roughly 830 meters depth two years ago by a U.S.
research
team. The ROV located it and sampled the soil sediments, the first
analysis of
which revealed concentrated methane and sulphide. Clamshells found will
be
studied to determine their age and the life span of the colony.
In
all, some 700 and 8,000 nautical miles were dedicated by
the Polarstern and its helicopter crews respectively to recording the
presence
and behaviors of marine mammals, which included Minke whales close to
the pack
ice edge and very rare beaked whale species near Elephant
Island.
“It
was surprising how fast such a new habitat was used and
colonized by Minke whales in considerable densities,” says
specialist Dr. Meike
Scheidat of Germany.
“They indicate that the ecosystem in the water column changed
considerably.”
Fisheries
investigations were carried out at islands west
and north of the Antarctic Peninsula.
The
results of 85 hauls over 19 days show the biomass of two Antarctic cod
species
has increased since a survey in 2003 while stocks of Blackfin and
Mackerel
Icefish has decreased. The results will contribute to fish stock
monitoring and
assessment ongoing under the Convention on the Conservation of
Antarctic Marine
Living Resources
Preliminary
findings from the voyage will be confirmed by
detailed analysis at the scientists' home institutes over the next few
years.
According
to Dr. Stoddart, a significant consequence in the Antarctic Peninsula of rising
temperatures is the slow decrease of sea ice and of the
planktonic algae that grows underneath.
These
algae feeds krill, small shrimp-like creatures, and
therefore represents the bottom rung on a marine food chain that
eventually
sustains the iconic large Antarctic species: penguins, whales and
seals. An
adult blue whale alone eats about 4 million individual krill per day.
“Algae
is a source of abundant, high-quality winter food and
is utterly central to the health of the whole ecosystem,”
says Dr. Stoddart,
adding that recent research by colleagues from the U.K.
shows krill stocks decreasing significantly around the Antarctic Peninsula.
However,
cautions Dr. Gutt: “Predicting the future of higher
levels in the food chain, e.g. animals living at the sea-floor or fish,
is very
difficult. It is for example clear that in the Larsen zone a major
biodiversity
shift will happen and the unique under-ice shelf system will disappear
in this
limited area, but we have to analyze carefully our raw data to provide,
as a
first step, a basis for such predictions. Besides modeling, further
observations and ecological field studies are necessary.”
“This
is virgin geography. If we don’t find out what this
area is like now following the collapse of the ice shelf, and what
species are
there, we won’t have any basis to know in 20 years’
time what has changed, and
how global warming has altered the marine ecosystem,” says
Gauthier Chapelle,
outreach officer for the expedition and biologist at the Brusselsbased
International Polar Foundation.
Says
Tarik Chekchak, Program Manager of the Cousteau
Society: “The Southern Ocean spans 35 million square
kilometers – 10% of
Earth’s ocean surface and ice shelves cover 1.5 million
square kilometers of
it. When Captain Cousteau explored Antarctica aboard the Calypso in
1972-73,
the Larsen B ice shelf was 3,250 square kilometers bigger and krill
abundance
in the Peninsula was much higher than today. The annual local
temperature has
risen 2.5 °C since the 1940’s.
“Impacts
of these changes on the Southern Ocean ecosystem
are substantial. Interplay between ocean circulation, sea ice extent,
ice shelf
cover and the iceberg’s mechanical action on the sea bed seem
to determine the
characteristics of some key planktonic and benthic communities. In a
changing
environment, the results of the CAML efforts are key to advancing our
ability
to understand our biosphere, inform public debate and allow
decision-makers to
lead us into a more sustainable future.”
##
Contact:
Terry
Collins
Census of Marine
Life
416-538-8712
terrycollins@rogers.com
This
text
derived from:
http://www.coml.org/embargo/embargo-feb.htm
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