A Stormy Winter Caused Antarctic Sea Ice to Melt

For decades, the sea ice around Antarctica expanded every winter, only to shrink rapidly in 2015. Now, a study reveals what has caused this drastic change.

Elephant seals have helped with the measurements.

‘The change in sea ice that we have witnessed is probably one of the biggest changes we have seen in the Earth’s climate system,’ says Theo Spira, lead author of the study published in Nature Climate Change.

The researchers have focused on the layer of cold water beneath the sea ice that prevents warmer deep water from rising and melting the ice from below. Until 2015, this layer helped the sea ice to grow, but beneath the surface it became increasingly weaker as the deep water warmed due to climate change.

Cold water layer

‘In 2015, the winds were really strong, and they caused the warm water below to break through the cold water layer,’ explains Theo Spira.

‘What we have shown is that, since 2015, the warm water has been able to reach the sea surface much more easily and has contributed to the decline in sea ice.’

The question that remains is whether the extent of sea ice around Antarctica will stabilise, continue to decline, or perhaps even recover.

The study highlights processes that have so far been poorly represented in climate models, and Theo Spira hopes that his research will contribute to better models in the future.

Elephant seals with sensors

He has compiled data from a range of different sources, including elephant seals fitted with sensors that measure water temperature, salinity and depth.

Elephant seals play a huge role in providing data from the Southern Ocean and in our understanding of the sea. They cover areas that are very difficult to reach, such as areas either around the edge of the sea ice or up through holes in the sea ice.

The discovery is also important for the role of Antarctic sea ice in our climate. The ice reflects the sun’s rays and blocks the exchange of heat between the ocean and the atmosphere.

The Southern Ocean is incredibly important for the global climate given its role in climate change. It is affected by climate change in terms of both heat absorption and carbon dioxide storage.

^{Cover image: Sea elephants fitted with sensors provide data from areas that are difficult for researchers to reach. The sensors are glued on and fall off after ten months. Photo: Dan Costa}