An Iceberg the Size of Luxembourg
As I am from Luxembourg, I well know how small a country it is — and yet, it is a country with all that entails, and so it has a size that is both geological and human, and thus Hannah Devlin’s Times newspaper headline & article strikes a deep chord:
Antarctic spits out iceberg the size of Luxembourg
by Hannah Devlin
An iceberg the size of Luxembourg has split off from the Antarctic continent and could disrupt global ocean patterns and weather systems for decades, according to scientists.
The 985 sq mile (2,550 sq km) block of ice was knocked off the Mertz Glacier Tongue, a spit of floating ice protruding from eastern Antarctica, on February 12 or 13.
It was dislodged by an older iceberg, known as B9B, which broke off in 1987.
Although the impact will not be felt for decades, the iceberg could block the production of cold, salty water, known as “bottom water”, which could lead eventually to cooler winters in the North Atlantic.
It could also have a negative impact on some of Antarctica’s wildlife, including a large colony of emperor penguins based near by.
A reduction in open water may mean they have to travel farther afield to find food.
“The ice tongue was almost broken already. It was hanging like a loose tooth,” said Benoit Legresy, who works at the Laboratory for Geophysics and Oceanographic Space Research in Toulouse.
His team, in collaboration with Australian scientists, has been monitoring the Mertz Glacier via satellite images and on the ground for a decade.
After remaining jammed against the Antarctic continent for 20 years, B9B began to drift last year, approaching the Mertz like a slow-motion battering ram.
“It gave it a pretty big nudge,” said Neal Young, a glaciologist at the Antarctic Climate and Ecosystems Research Centre in Tasmania.
Since the collision, the iceberg and the newly mobile B9B, which is about the same size, have moved into an area called a polynya. Distributed across the Southern Ocean, polynyas are zones producing dense water, super-cold and rich in salt, that sink to the sea bottom and drive the conveyor-belt-like circulation around the globe.
If the icebergs move east and run aground, or drift north into warmer seas, they will have no impact on the global convection system.
But if they stay in the area — which scientists say is likely — they could partly block the production of the dense water, essentially putting a lid on the polynya’s action.
The Mertz Glacier Polynya accounts for about 20 per cent of the bottom water in the world, and so over decades — the timescale on which the currents circulate — the impact could be significant.
A slowing down of production of bottom water would mean less oxygen going into the deep currents that feed the oceans.
“There may be regions of the world’s oceans that lose oxygen, and then of course, most of the life there will die,” said Mario Hoppema, chemical oceanographer at the Alfred Wegener Institute for Polar and Marine Research in Germany.
However, Michael Meredith, polar oceans specialist at the British Antarctic Survey, said any measurable change in oxygenation was likely to be localised to Antarctica.
The carving off of ice shelves and collapse of glaciers are part of Antarctica’s natural cycle, but man-made climate change could accelerate the processes.
“Obviously when there is warmer water, these ice tongues will become more fragile,” Dr Legresy said.
The Mertz Glacier Tongue has been under close scientific scrutiny for the past decade and is fitted with GPS beacons and other measuring instruments, meaning scientists will have a record of the calving event — before, during and after.
“We are using the ice tongue as a laboratory to study the processes that might be impacted by climate change, including calving, ocean temperature, sea level change,” Dr Legresy said.