The Iceland hotspot's ancient heat is still nudging ice toward the sea.
Beneath Greenland's ice sheet — two miles thick in places, ancient and vast — the ground is not uniform. It is hot in some places and cold in others, and those differences matter enormously for how the ice above it moves, melts, and eventually finds its way into the sea. A new study from researchers at the University of Ottawa and the University of Twente has, for the first time, mapped those temperature variations in three dimensions, and the picture they've produced is already changing how scientists think about sea level rise.
The work was led by Parviz Ajourlou, a PhD graduate at the University of Ottawa, who served as the study's first author. Working alongside Dutch colleagues from the University of Twente and experts from GEUS — the Geological Survey of Denmark and Greenland — Ajourlou ran hundreds of thousands of computer simulations on supercomputers operated by the Digital Research Alliance of Canada. The inputs were diverse: satellite data, seismic readings, gravity anomalies, heat flow measurements. The output was something no one had built before — a coherent, three-dimensional thermal portrait of the rock beneath Greenland and northeast Canada.
What that portrait revealed is a story written in deep time. Millions of years ago, Greenland drifted over the Iceland hotspot, a plume of superheated material rising from deep within the Earth. That passage left marks. Certain regions of bedrock were scorched and altered; others were not. The result is a patchwork of thermal conditions that persists today, invisible beneath the ice but consequential for everything happening above it.
The mechanism is straightforward once you see it. Where bedrock runs hotter, the base of the ice sheet warms more easily, reducing friction and allowing ice to slide faster toward the ocean. Where bedrock is cooler, the ice grips more tightly, moving more slowly. Previous climate models treated the subsurface as more or less homogeneous, smoothing over these lateral variations. The new models do not. They capture the patchwork, and in doing so, they change the math on ice dynamics.
Professor Glenn Milne, who chairs Earth Sciences at the University of Ottawa and was a senior contributor to the study, framed the practical stakes plainly: temperature variations in the bedrock directly shape how the ice sheet and the ground beneath it interact, and getting that interaction right is essential for interpreting the signals scientists use to track ice loss — land motion, gravity changes, surface elevation shifts. Without accurate subsurface temperatures, those signals are harder to read.
The urgency behind this work is not abstract. Greenland is currently shedding roughly 270 gigatons of ice every year. That number is already baked into rising seas around the world, and it is expected to grow as Arctic temperatures continue climbing. The difference between a good sea level forecast and a poor one is, in practical terms, the difference between a coastal city that builds adequate defenses and one that doesn't. Ajourlou put it directly: better models of ice-bedrock interaction produce better forecasts of future sea level rise.
The collaboration itself reflects how the problem demands to be approached. The University of Twente brought deep expertise in geophysical modeling; GEUS contributed decades of on-the-ground knowledge about Greenland's ice. Ottawa's team provided the computational architecture and the Earth sciences framework to tie it together. The supercomputing resources made the scale of simulation possible at all.
What the study ultimately offers is a more honest accounting of what lies beneath one of the planet's most consequential ice sheets. The Iceland hotspot's ancient heat is not a historical curiosity — it is an active variable in the equations that will determine how much ocean cities from Miami to Mumbai will have to contend with in the decades ahead. The next step is incorporating these refined thermal models into the broader climate projections that governments and planners rely on.
Notable Quotes
Temperature variations directly influence the interaction between the ice sheet and the bedrock, which is essential for interpreting observations of land motion and gravity changes.— Prof. Glenn Milne, University of Ottawa Earth Sciences
By improving how we model ice-earth interactions, we can better forecast future sea level rise.— Parviz Ajourlou, first author and University of Ottawa PhD graduate
The Hearth Conversation Another angle on the story
Why does it matter what the temperature is under the ice? The ice is melting from above, isn't it?
From above, yes — but the base of the ice sheet is where it meets the ground, and that contact point controls how fast the ice moves. Warmer bedrock means less friction, faster flow toward the sea.
So the geology is doing something active, not just sitting there.
Exactly. The rock beneath Greenland isn't passive. It has a thermal history — specifically, the island's ancient drift over the Iceland hotspot — and that history is still shaping ice behavior today.
What was missing before this study?
Three-dimensional resolution. Previous models treated the subsurface as relatively uniform, which meant they were missing the patchwork of hotter and cooler zones that actually exist. That's a significant gap when you're trying to model ice dynamics precisely.
How do you even measure heat under two miles of ice?
You don't measure it directly. You fuse indirect signals — seismic wave speeds, gravity anomalies, satellite data, surface heat flow — and run enormous numbers of simulations until a coherent thermal picture emerges. That's what the supercomputers were for.
Two hundred seventy gigatons of ice per year — how should I hold that number?
Think of it as a permanent, accelerating transfer from land to ocean. Every gigaton raises sea levels a fraction of a millimeter. Multiply that across decades and the fractions become feet.
Does this study change the forecast, or just sharpen it?
It sharpens it. The direction of the forecast — more melt, higher seas — was already established. What this adds is precision about where and how fast, which is what planners actually need.
Is there something almost eerie about ancient geology driving a modern crisis?
There is. The Iceland hotspot did its work millions of years ago and moved on. But the thermal signature it left in the rock is still nudging ice toward the sea right now. The past doesn't stay past.