The deepest point on continental Earth has been identified in East Antarctica, under Denman Glacier.
This ice-filled canyon reaches 3.5km (11,500ft) below sea level. Only in the ocean are the valleys deeper still.
The discovery is illustrated in a new map of the White Continent that reveals the shape of the bedrock under the ice sheet in unprecedented detail.
Its features will be critical to our understanding of how the polar south might change in the future.
For comparison, the lowest exposed land on Earth, at the Dead Sea shore, is just 413m (1,355ft) below sea level.
The new finding shows, for example, previously unrecognized ridges that will impede the retreat of melting glaciers in a warming world; and, alternatively, a number of smooth, sloping terrains that could accelerate withdrawals.
“This is undoubtedly the most accurate portrait yet of what lies beneath Antarctica’s ice sheet,” said Dr Mathieu Morlighem, who’s worked on the project for six years.(BBC)
In contrast to the situation in the Transantarctic Mountains, BedMachine Antarctica finds few impediments to the rapid retreat of Thwaites Glacier. Roughly the size of the UK, this mighty ice stream terminates in the Amundsen Sea in the west of the continent.
It worries scientists because it sits on a bed that slopes back towards the land – a geometry that tends to assist withdrawal. And the new map reveals only two ridges, some 30km and 50km upstream of Thwaites’ current grounding line, that could act as potential brakes. Go past these and the melting glacier’s pull-back could be unstoppable.
BedMachine Antarctica will be fed into climate models that try to project how the continent might evolve as temperatures on Earth rise in the coming centuries.
Getting realistic simulations out of these models depends on having more precise information on the thickness of the ice sheet and the type of terrain over which it must slide.
Co-worker Dr Emma Smith from Germany’s Alfred Wegener Institute uses this analogy: “Imagine if you poured a bunch of treacle on to a flat surface and watched how it flowed outwards. Then pour the same treacle on to a surface with a lot of lumps and bumps, different slopes and ridges – the way the treacle would spread out would be very different. And it’s exactly the same with the ice on Antarctica,” she told BBC News.