Thinning, acceleration and calving of Petermann Glacier, northern Greenland
Satellite observations reveal that Petermann Glacier in northern Greenland is undergoing rapid thinning, acceleration, and a major calving event driven by anomalously warm ocean waters and reduced sea ice, signaling a dynamic imbalance that threatens significant sea-level rise.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Imagine the Greenland Ice Sheet as a giant, frozen fortress guarding the Arctic. At its northwest corner, there's a massive "ice tongue" called Petermann Glacier, jutting out into the ocean like a frozen arm. For a long time, scientists thought this arm was tough, stable, and barely bothered by the changing weather around it. But a new study reveals that this frozen arm is actually getting wobbly, thin, and fast—and it's about to snap off a huge chunk.
The Great Crack-Up
Think of the ice shelf like a giant sheet of ice on a pond. Recently, two massive cracks (called rifts) started forming on this sheet. One crack began in 2010 and grew slowly, while a second one started in 2013. For years, the second crack was just a slow creep, but then it suddenly sped up. In the summers of 2024 and 2025, this crack raced forward, growing by about 3.1 km in just two weeks and another 3.6 km the next summer.
Now, these cracks have stretched almost all the way across the ice shelf. It's like a zipper that's been pulled almost shut, leaving only a tiny, fragile bridge of ice (less than 500 meters wide) holding the front part together. The scientists predict that this front section, covering about 257 km², is about to break off. That's an iceberg twice as big as the massive one that broke off in 2012. When it goes, the glacier's edge will retreat to its most backward position ever recorded, shrinking the ice shelf by 22%.
The Speeding Up
Here's where it gets interesting. Usually, when a chunk of ice breaks off, the glacier behind it might speed up for a little bit and then settle down. But Petermann is different. The study shows that the glacier has been speeding up steadily for a whole decade.
Imagine a runner who suddenly starts jogging faster and faster, not just for a sprint, but for ten years straight. The ice on the floating shelf is moving about 60% faster than the ice on the land behind it. Even more surprising, this "running faster" signal has traveled more than 50 km inland, deep into the grounded part of the glacier. This suggests the glacier is in a state of "dynamic imbalance"—it's losing ice to the ocean faster than nature can replace it from the snow above.
The Secret Culprit: Warm Water and Missing Ice
Why is this happening? The paper points to two main suspects working together.
First, the ocean water underneath the ice shelf has been unusually warm. Think of the water as a hot bath that's been heating up since 2011, with the warmest pulses hitting between 2016 and 2019. This warm water is melting the bottom of the ice shelf from below, making it thinner and weaker. The study found that the ice shelf lost about 11% of its total thickness between 2012 and 2020, mostly due to this underwater melting.
Second, the "sea ice blanket" that usually protects the fjord has been missing. Normally, landfast sea ice (ice that sticks to the shore) acts like a shield, stopping wind from pushing warm water up into the fjord. But in recent years, especially between 2016 and 2019, this protective blanket was largely gone. Without it, the wind could push that warm water right up against the glacier, speeding up the melting.
What It's NOT
The researchers are careful to say what isn't causing this. They looked at whether the glacier was speeding up because of surface meltwater (rain and snow melting on top). While there was some extra runoff, the timing didn't match the rapid thinning of the ice shelf. The main driver appears to be the ocean, not the sky.
They also checked if the glacier was speeding up because the "grounding line" (where the ice lifts off the bedrock) moved back. While the grounding line did retreat a bit between 2015 and 2018, the glacier had already started speeding up before that happened. So, the retreat wasn't the initial trigger; it was likely a result of the warming ocean and thinning ice.
The Big Picture
The study suggests that Petermann Glacier is no longer the stable giant it was once thought to be. The combination of warm ocean water eating away at the bottom and the loss of protective sea ice has weakened the ice shelf's ability to hold back the inland ice.
If this trend continues, the glacier could become a much bigger contributor to rising sea levels. The ice shelf holds back a massive amount of ice—enough to raise global sea levels by 0.41 meters if it all melted. With the shelf thinning and the glacier accelerating, the "brakes" are failing. The scientists say that while we know the ice is changing, the exact mix of how ocean heat, sea ice, and the glacier's own structure interact is still a complex puzzle. But one thing is clear: the ice shelf is about to lose a huge piece, and the glacier behind it is waking up.
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