Antarctica is a bit of a paradox. While the continent’s sea ice is breaking records for thickness and extent, it also hosts some of the world’s fastest melting glaciers. Now researchers in the US suggest an influx of warm water thinned some of West Antarctica’s ice shelves, leading to the rapid retreat of three glaciers.
Led by Ala Khazendar from the California Institute of Technology, the team used data collected by NASA’s Operation Icebridge – which sends aircraft to fly over the poles – to study melting from the Smith, Pope and Kohler Glaciers.
They found hundreds of metres of the glacial ice melted between 2002 and 2009, supporting the hypothesis that in the mid-2000s, the West Antarctica’s Amundsen Sea bay was flooded with warm water.
“To me, an interesting and satisfying part was how our results to seem to fit well with what other research was revealing about the changes in the Amundsen Sea region,” Khazendar says of the findings, published in Nature Communications.
Ice shelves are thick, vast swathes of ice that poke out from the land and into the sea. But warm water can squeeze into ice shelf cracks, eroding them from the bottom up.
This can have a domino effect if the water penetrates the grounding line – the zone where land ice starts to float in water. If the grounding line takes in warm water, contact between bedrock and glacier ice is weakened and glaciers retreat rapidly.
Until now, no one knew just how much ice was lost this way.
But with NASA aircraft scanning the icy plains, the researchers measured that Smith glacier suffered the most of the three, with as much as 70 metres in length and almost 500 metres in thickness of solid ice disappearing each year.
So what’s warm water doing at the bottom of the world anyway?
Well, it’s not warm in the sense a bath might be warm. Sitting a few degrees above freezing, the relatively warm, salty water is called Circumpolar Deep Water. It’s a blend of the world’s oceans and travels across a continental shelf at a depth of more than 300 metres.
From 2009 until 2014, the authors write the warm water eased up and slowed Kohler and Pope’s retreat.
But for Smith Glacier, it might have been too late. The ice at the grounding line had already formed a deep cavity. Melting continues today.
Khazendar says the study was motivated by previous studies on the rapidly vanishing Thwaites Glacier nearby. He noticed, though, that the Smith Glacier had the fastest retreating grounding line.
“I started thinking that because the retreat signal in the case of Smith Glacier was so large, there might be a better chance of detecting some of the underlying processes,” he says.
He says the results from this study will be used to develop a model that would simulate the processes at the ice-ocean connection point, to better understand how ice shelves evolve and help predict future melting.