BBC News
February 2010
Any disruption to the net flow of bottom water could result in a weakening in the deep ocean circulation system, which plays a key role in the global climate system.
A vast iceberg that broke off eastern Antarctic earlier this month could
disrupt marine life in the region, scientists have warned.
They say the iceberg, which is 78km long and up to 39km wide, could have
consequences for the area's colonies of emperor penguins.
The emblematic birds may be forced to travel further afield to find food.
The iceberg calved from the Mertz Glacier Tongue after it was hit by another
huge iceberg, called B9B.
"It is a very active area for algae growth, especially in springtime,"
explained Dr Neal Young from the Australia-based Antarctic Climate and
Ecosystems Co-operative Research Centre.
"There are emperor penguin colonies about 200-300km away to the west. They
come to this area to feed, and seals in the area also come to get access to
the open water," he told BBC News.
He suggested that a change in the availability of open water could affect
the rate of food production, which would have an impact on the amount of
wildlife it could sustain.
"If the area gets choked up (with ice), then they would have to go elsewhere
and look for food." Changing landscape The calving of the iceberg, which has
an estimated mass of 700-800bn tonnes, has changed the shape of the local
geography, Dr Young explained.
Changing Landscape
The calving of the iceberg, which has an estimated mass of 700-800bn tonnes,
has changed the shape of the local geography, Dr Young explained.
"We have got two massive icebergs that - end to end - create a fence of
about 180km.
"So the area's geography has changed from a situation where we effectively
had a box in which two sides were open ocean," he told BBC News.
"Now we have a fence across one side of the box."
Before the formation of the iceberg, the Mertz Peninsula provided the right
conditions for a polynia - an expanse of open water surrounded by sea-ice -
to exist.
"Winds blow off the coast and clear anything in that region, including sea
ice, exposing open water," Dr Young explained.
He added that as well as providing a feeding site for the region's wildlife,
the polynia also was a key production site of "bottom water"; very cold,
dense water that sinks to the ocean floor.
"Sea ice is relatively fresh compared to sea water, so the more sea ice you
have (in the surrounding area), the more salt that is left in the remaining
open water."
The rise in the concentration of salt increases the water's density, causing
it to sink to the bottom of the ocean.
"This area around the Antarctic coastline, of which the Mertz Peninsula is
one part, produces about one quarter of the Antarctic's bottom water, but
the Mertz polynia is a major contributor," Dr Young said.
He added that the new iceberg had shortened the length of the Mertz Glacier
Tongue, which could result in pack ice entering the area and disrupting the
polynia.
"That means that the bottom water production rate... will decrease.
"The bottom water spills over the continental shelf, flows down the
continental slope into the deep ocean."
This process helps drive the "conveyor belt" of currents in the Southern,
Pacific and Atlantic Oceans.
Any disruption to the net flow of bottom water could result in a weakening
in the deep ocean circulation system, which plays a key role in the global
climate system.
'Natural laboratory'
However, the researchers say the changes to the region triggered by the
formation of the new iceberg will not shut down the circulation system or
affect the world's climate.
"Large icebergs always attract a lot of attention due to their scale,"
observed Dr Michael Meredith from the British Antarctic Survey, who was not
involved in the research.
"Bottom water is indeed an important part of the global ocean overturning
circulation and hence climate," he told BBC News.
"There are also a number of other locations of bottom water formation,
however. So, it's unlikely that a large-scale sustained change of the order
of magnitude required for a global climate impact will happen from this one
event.
"The more important thing, I think, is that this event has been closely and
carefully monitored by scientists, who will now look at the processes
whereby such calvings can impact on the ocean and the ecosystem - and
studying this natural laboratory will add to our knowledge of how the
Antarctic system works."
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