Never before have researchers recorded so little sea ice around the Antarctic during the summer months of the southern hemisphere. Half of Weddell Sea is currently not covered with ice. As Barbara Barkhausen in Sydney reports, this could even hasten the collapse of the Larsen C ice shelf.
Traditionally, the ice in the Antarctic has another seven to ten days to melt before the Antarctic summer comes to an end and the cold autumn storms freeze the seawater all over again.
But conventional yardsticks don’t appear to be working this summer, said Jan Lieser, a German meteorologist who works at the Antarctic Climate and Ecosystems Cooperation Research Centre in Hobert on the island of Tasmania.
According to the sea ice expert, the Antarctic winter was already cut short by four weeks, which in turn has meant that the melting season was four weeks longer than usual. The coming weeks will now show whether this pattern will continue in the coming autumn.
Only half of Weddell Sea is frozen
The sea ice is already at a record low. Satellite data from the National Snow and Ice Data Center (NSIDC) in the US reveals that only 2,287 million square kilometres was covered with ice at the beginning of the week.
The last comparable low of 2,289 million square kilometres was measured in February 1997, 18 years after records began to be kept.
“1997 was the last abnormal year,” said Lieser, who has never before witnessed the normally frozen Weddell Sea with so much open sea. In his opinion, climate change certainly plays a role in the record low, even if “multiple reasons are at play, such as a stronger west wind drift”.
Researchers discovered for themselves just a few weeks ago that the Antarctic had thawed while they were on a research expedition to the southern continent. Their icebreaker could “drive with ten knots through the sea ice” – it was so brittle, said Lieser, who also detected unnaturally high water temperatures on the sea surface.
“Antarctic has flipped the script”
Lieser fears that the sea ice could reduce even further in the coming years and fall below the 2 million square kilometre mark. If this were to happen, it would show that the Antarctic is now following the developments observed by researchers for years now in the Arctic.
“The Arctic has typically been where the most interest lies,” Walt Meier, a NASA scientist at NSIDC, said last year when the trend towards the sea ice melt was already indicated.
But “the Antarctic has flipped the script and it is southern sea ice that is surprising us.”
Despite reports of collapsing ice shelves, the Antarctic had always seemed better at coping with global warming than its northern counterpart. In November 2014, for example, an underwater sea robot used to develop a 3D map of sea ice even recorded that the ice lawyer was even thinker than once thought.
This positive news now seems moot.
Larsen C could collapse faster
The shrinking sea ice could now pose a problem for the still-intact ice shelves in the region. The Larsen A and B ice shelves already broke apart in 1995 and 2002, but Larsen C is still intact – although just barely: warmer air temperatures have already begun to shrink the ice shelf from above, while warmer ocean currents are doing their part to weaken it from below.
The considerably lower mass of sea ice this year could further hasten the threatening collapse of the ice shelf.
As Lieser explained: “Less sea ice also means less protection as it lacks the buffer effect. And without a buffer, the edges of the ice shelf are exposed to more wind and waves.”