Heat in Earth’s mantle may explain uneven ice loss in Greenland

Researchers developed 3D temperature models to map deep heat beneath Greenland and northeastern Canada, uncovering strong east-west differences that influence ice behavior.

The study shows that the upper mantle – the hot rock beneath Earth’s crust – can differ in viscosity by as much as a thousand times from one region to another.

Led by the University of Ottawa with partners in Denmark and the Netherlands, the team says that deep-Earth details are key.

Geothermal heat under Greenland

Basal melting depends in part on basal heat flux – heat from Earth’s interior that warms ice from below.

Earlier mapping traced a band of elevated geothermal heat under Greenland that is consistent with an Iceland plume track. 

Greenland’s recent history highlights why the deep signal matters. From 1992 to 2020, the island lost about 5.4 trillion short tons of ice, according to a previous assessment. 

The latest study was led by Dr. Parviz Ajourlou at the University of Ottawa. His research focuses on joint inversion and Earth rheology beneath ice covered regions.

“Our new regional temperature models reveal significant lateral variations in the Earth’s thermal structure beneath Greenland,” said Dr. Ajourlou. Those variations help scientists link tectonic history to present-day ice behavior.

Deep heat shapes ice behavior

Greenland sits on crust shaped by volcanic activity, slow plate motions, and changes inside the mantle.

These forces created a mix of hotter and cooler zones beneath the island, and those zones change how the ice sheet moves.

Warmer rock reduces resistance where the ice meets the ground, which lets ice slide more easily in some areas.

Scientists have been working to sort out how much the deep structure matters compared to surface climate. They now see that temperature contrasts beneath the island help explain why some regions thin faster than others.

Heat-driven patterns across Greenland

The discovery also helps explain why satellite instruments detect uneven patterns of gravity and height change across the ice sheet. The team noted that deep temperature variations make a difference even in colder zones. 

Slight shifts in heat at depth can alter the strength of the bedrock, and this affects how the crust sinks or rises when ice is added or removed. These movements show up in GPS data as slow tilts in the land.

Researchers are now testing how these deep patterns interact with ocean driven melt near the coast. They expect that pairing deep-Earth models with coastal observations will reveal where thinning might speed up in coming decades.

That combined view brings them closer to understanding the full picture of Greenland’s response to a warming world.

Hotspot beneath the ice

The temperature pattern lines up with a hotspot track, a path left by a long-lived mantle plume in moving crust. Independent seismic work has imaged a crustal corridor and warmer mantle beneath parts of Greenland. 

Thermal contrasts also affect how the solid Earth bends under loads. That flexing sets the pace of vertical land motion and changes the stress at the base of the ice.

By fitting both past sea-level data and today’s GPS-measured uplift, the team’s 3D viscosity field ties deep structure to surface change. 

From deep heat to rising seas

The group built a probabilistic model that merges seismic velocities, gravity anomalies, and heat flow into one solution. Scientists call this a joint inversion, a method that combines multiple datasets to reduce uncertainty in each.

The temperature fields feed into glacial isostatic adjustment, the slow rebound of Earth’s crust after ice melts. 

Tighter constraints on viscosity reduce uncertainties in ice mass change and the gravity measurements used to track modern loss.

Recent observations show pressure on the system today. In 2023, Greenland lost about 195 billion short tons of ice, a sharp annual drop documented by the Copernicus Climate Change Service indicator. 

Model outcomes still hinge on the heat map under the ice. A 2024 modeling analysis found that different geothermal maps produced conflicting basal thaw patterns across about one third of the sheet.

How this changes forecasts

The new maps let ice-sheet and sea-level models use temperature and viscosity that vary in three dimensions instead of simplified averages. 

This makes it easier to distinguish ice changes driven by the ocean and atmosphere from those controlled by the solid Earth.

“This work is a good illustration of how our knowledge of the solid Earth enhances our ability to understand the climate system,” said Dr. Ajourlou. 

By capturing a clearer picture of ice-Earth interactions, the research will lead to more reliable projections of Greenland’s contribution to future sea-level rise.

The study is published in the journal Proceedings of the National Academy of Sciences.

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