The size of Delaware, four times as big as London, quarter the size of Wales – whatever the description it is clear that one of the largest icebergs ever recorded has calved from the Arctic ice shelf, a NASA satellite confirmed on 12 July.
Weighing over a trillion tonnes, the 5 800 square kilometre section of the Larsen C ice shelf has been breaking away for months. Researchers from the MIDAS project
, UK, have been monitoring Larsen C for many years, following the collapse of the Larsen A ice shelf in 1995 and the sudden break-up of the Larsen B shelf in 2002. They report that the calving terminated a rift that has been developing over a year. The calving of this iceberg leaves the Larsen C Ice Shelf reduced in area by more than 12%, and the landscape of the Antarctic Peninsula changed forever. This is the furthest back that the ice front has been in recorded history and MIDAS is going to be watching very carefully for signs that the rest of the shelf is becoming unstable.
The impact of a free floating iceberg
The question now being asked is whether the berg will interrupt shipping lanes. A drift pattern map of icebergs that have been tracked around the Antarctic continent is available on the BBC
. As the site reports, ‘This collective history strongly suggests the Larsen block will head for the South Atlantic.’
Currents, wind direction and gravity all play a role in the direction the berg will take. Due to the winds, water levels are around half a metre higher near Antarctic coast in comparison with the centre of the ocean. This forms a slope down which the berg will float under its own weight, but not in a straight line. The Coriolis effect, formed by by the earth’s rotation, will cause the iceberg to veer left. The waters around the continent are shallow and if the berg scrapes along the bottom it will spin or stall, gouging a trough along the sea floor. This is called ‘kedging’.
It might get stuck firmly on some high-rise topography on the ocean shore to form a semi-permanent ice island in the Weddell sea, ‘We''ve seen that before,’ said Dr Anna Hogg from Leeds University said. But the expectation is that the iceberg will float and grind northwards in the near-coast currents flowing along the peninsula.
‘The icebergs often shoal and pivot or spin around their grounding point, resulting in stop and go motion or a change in direction. So, the iceberg from Larsen C could take some time before it escapes the shallow [waters] of the western Weddell Sea,’ Dr Mark Drinkwater, one of the European Space Agency’s senior Earth observation scientists, told