Something strange has been happening with Antarctic sea ice this week

Resupply at Davis is usually over the sea ice from ship to shore. Image: Bill de Bruyn

Australians working at Antarctic bases have recently noticed significant shrinkage in winter sea-ice.

They say the sea ice coverage as started its annual retreat early and has been setting new daily record lows for much of the past week.

This comes after winter sea ice around Antarctica reached a new record high in September 2014 when it exceeded 20 million square kilometres for the first time since satellite measurements began in 1979.

This year, Antarctic sea ice started its spring retreat four weeks earlier than average, after peaking at 18.5 million square kilometres on August 28, close to the lowest annual maximum on record.

The ice retreat could cause problems for the Australian expeditioners.

The Australian Antarctic Division has contingency plans for an aerial resupply of Davis station because of the early retreat of the winter sea-ice.

Davis usually gets supplied across the sea ice from Australia’s icebreaker Aurora Australis. If the ice isn’t thick enough, a helicopter will need to be used to move cargo.

“Within the space of just two years, we have gone from a record high winter sea-ice extent to record daily lows for this point in the season,” says Dr Jan Lieser from the Antarctic Climate and Ecosystems Cooperative Research Centre.

“This is a fascinating change, and a great reminder that we are dealing with an extremely variable component of the climate system.

“It’s also a reminder of why it can be unwise to leap to conclusions about the link between Antarctic sea ice and climate change on the basis of one or two years of data.”

This chart shows the recent steep fall in sea ice. The dark blue line is the 2016 sea ice. The light blue area is the maximum and minimum recorded ice between 1979 and 2015. Black is the average.

Source: Antarctic Climate and Ecosystems Cooperative Research Centre

Dr Lieser says the long-term trends are most important.

Sea ice, which has an important impact on global climate, covers and affects up to 40% of the Southern Ocean surface area during winter.

Its annual cycle of advance and retreat represents one of the greatest seasonal changes to the Earth’s surface.

“It’s likely that last year’s powerful El Nino event is playing a role in this year’s sea-ice distribution, but there is also a likely contribution by weather events at the local scale,” says Lieser.

“Sea ice cover in the Arctic has been reducing steadily over the past several decades, and climate models also predict that over time sea ice will also reduce around Antarctica.”

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