It’s hard to imagine, but Antarctica wasn’t always covered in ice. This huge continental landmass, back in the age of the dinosaurs, was a lush forested landscape, teeming with large creatures and critters alike. Nowadays, shielded by the largest ice sheet on the planet, we are only beginning to be able to visualize this trapped ancient realm below, full of canyons and mountain ranges the likes of which we’d never seen.
It’s still hiding plenty of secrets, and a rather neat new study published this week in Scientific Reports has uncovered yet another. Far below the ice at the heart of the continent, there appears to be an anomalous hotspot. Something’s cooking the South Pole from below.
A team, led by the British Antarctic Survey (BAS), were using aircraft equipped with radar-penetrating data to peer through the South Pole’s thick ice when they made the discovery. Although several satellites owned by the European Space Agency (ESA) have or had been keeping an eye on the ice thickness and underlying geology through various means, the highest-latitude parts of Antarctica simply couldn’t be covered with their orbits.
To fill in this informational gap, those aforementioned aircraft were recently brought to fly directly over these areas to see what’s happening down below. Appropriately named the PolarGAP project, this ESA-funded program quickly revealed a hidden, dramatic world. Just recently, it found three deep scars within the ground beneath the ice, with one clocking in at an impressive 350 kilometres (218 miles) in length.
It turns out that, beneath several kilometres of ice, there is a 100-by-50-kilometre (62-by-31-mile) warm patch, which according to the BAS is roughly twice the size of Greater London. The ice here is actually drooping over it, as the patch – whose heat is emanating from the bedrock – is slicing off around 6 millimetres (0.2 inches) of ice per year, creating concealed streams that slip out toward the coast.
The heat flow in the area is 120 milliwatts per square meter. That doesn’t mean much on its own, but it’s over twice what’s expected from this part of East Antarctica. Clearly, something’s going on with the bedrock beneath the ice, but what?
Although a curiosity for sure, this hotspot isn’t alone in Antarctica. They’ve been detected before: heat – generated by the primordial embers left over from the planet’s formation, or from radioactive materials – is always escaping from the bowels of the planet.
Some of this heat has shown up underneath Antarctica’s ice, as was displayed by a rather beautiful map produced by the BAS last year. You can see that the Antarctic Peninsula, along with some of Western Antarctica, is a fair bit hotter than the rest of the continent. That’s thought to be because a rising mantle plume in that area is slowly cooking the crust, which explains why there are so many volcanoes in that region.
East Antarctica’s geology, as this map shows, is relatively frigid. This makes sense, because the rock, in this case, is stupendously old. This part of Antarctica is made up of cratons, which are huge masses of continental crust that have remained in a state of stability for billions of years. In fact, in East Antarctica the rocks date back to the Precambrian Eon, a huge expanse of time starting with the birth of Earth 4.6 billion years ago to around 541 million years ago, when complex life first exploded into the fossil record.
It’s a freakishly calm piece of the overall plate tectonic jigsaw. For some time, it was thought to be lacking in earthquakes – odd for such a massive place being stretched by tectonic forces over time – but a recent study found that there are more shakes there than scientists originally detected. Nevertheless, it’s still a fairly tranquil location: as the authors of this new study point out, it hasn’t experienced a major tectono-thermal event for 500 million years. That means it’s not been rifted apart or broken up or experienced any profound crustal melting for a considerably long time.
This new hotspot, then, is a little weird and unexpected. Previous seismic data suggests part of the rising mantle beneath West Antarctica could be sneaking its way to the South Pole, but this warm zone is too isolated for this to be the case. There’s no obvious signs of embryonic volcanism going on either.
Instead, they looked to part of Central Australia for inspiration. Despite it also being a very stable craton, there’s an anomalously high flow of heat from the ancient rock there too. Rocks like this often have a high concentration of radioactive components in them, which as they decay produce plenty of heat. Therefore, the driver of this anomalously warm zone near the South Pole is a naturally radioactive cache.
The team also suspect that in order for this area to be quite so hot, you’d also need to have circulating, hot hydrothermal fluids in the region. They’d be making their way along a major fault line, created as the entire continent is stretched apart slowly over time.
This remains a hypothesis, as the rocks haven’t been directly examined, but if corroborated, it’s likely that other hotspots like this could be found elsewhere in Antarctica. This isn’t ideal: by creating subglacial rivers, it’ll simply lubricate fast-flowing ice on its way to the coast.
As you might expect, it’s impossible to talk about this new discovery without mentioning climate change. Don’t worry for now; the authors of the study stress that this process, which has been taking place for millennia or even millions of years, isn’t currently contributing to changes in the ice sheet cover. It’s just not potent enough.
In the future, however, it could make the area more sensitive to the effects of climate change, but it’s difficult to say how.
Antarctica is huge, and diverse. Thanks to the different arrangements of sea-floating ice shelves and land-trapped ice sheets, all sitting on different bedrock topographies that vary wildly over this truly enormous continent, the ice here doesn’t move or flow of melt in a homogenous way.
The entire continent also doesn’t respond evenly to the warming air and ocean water around it. According to the BAS, the Antarctic Peninsula and much of West Antarctica warmed significantly in the last half-century or so. In other parts, temperatures have remained somewhat stable. (Saying that, it’s increasingly clear that Antarctica, including the once-stable East Antarctica, is now shedding unprecedented amounts of ice.)
Geothermal hotspots form a small but important part of the puzzle too. However, as the BAS notes, “of the basic information that shapes and controls ice flow, the most poorly known about is this heat.” So with that in mind, this study isn’t just about a fun mystery; it’s about a detective story that affects the entire base of the world.