The nice ice streams of the Antarctic and Greenland are like frozen rivers, carrying ice from the huge inland ice sheets to the ocean — and a change of their dynamics will contribute significantly to sea-level rise. As a way to estimate just how much sea levels will rise, climate researchers depend on computer simulations of the ice streams. Until now, they’ve based these simulations on an assumption that the ice streams flow slowly but steadily into the ocean like thick honey.
Nonetheless, satellite measurements of the flow speed of ice streams show that such simulations are inaccurate and have shortcomings to appropriately reflect reality. This results in considerable uncertainties in estimates of how much mass the ice streams are losing and the way quickly and the way high sea levels will rise.
Ice streams each judder and flow
Now, a team of researchers led by ETH professor Andreas Fichtner has made an unexpected discovery: deep throughout the ice streams, there are countless weak quakes going down that trigger each other and propagate over distances of a whole bunch of metres. This discovery helps to clarify the discrepancy between current simulations of ice streams and satellite measurements, and the brand new findings must also impact the best way ice streams are simulated in the long run.
“The idea that ice streams only flow like viscous honey isn’t any longer tenable. In addition they move with a relentless stick-slip motion,” says Fichtner. The ETH professor is confident that this finding will probably be integrated into simulations of ice streams, making estimates of changes in sea level more accurate.
Riddles referring to ice cores resolved
Furthermore, the ice quakes explain the origin of diverse fault planes between ice crystals in ice cores obtained from great depths. These fault planes are the results of tectonic shifts and have been known to scientists for many years, although no explanation had been found for them until now.
“The undeniable fact that we have now discovered these ice quakes is a key step towards gaining a greater understanding of the deformation of ice streams on small scales,” explains Olaf Eisen, Professor on the Alfred Wegener Institute and one in every of the study’s co-authors.
The study by this international research team led by ETH Zurich has just been published within the journal Science and likewise involved researchers from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), the University of Strasbourg, the Niels Bohr Institute (NBI), the Swiss Federal Institute WSL and other universities.
Fire and ice are related
The undeniable fact that these ice quakes can’t be observed on the surface and have subsequently remained undiscovered until now’s resulting from a layer of volcanic particles positioned 900 metres below the surface of the ice. This layer stops the quakes from propagating to the surface. Evaluation of the ice core showed that these volcanic particles originate from an enormous eruption of Mount Mazama in what’s now Oregon (USA) some 7,700 years ago. “We were astonished by this previously unknown relationship between the dynamics of an ice stream and volcanic eruptions,” Fichtner recalls.
The ETH professor also noticed that the ice quakes start from impurities within the ice. These impurities are also leftovers from volcanoes: tiny traces of sulphates that entered the atmosphere in volcanic eruptions and flew halfway around the globe before being deposited on the Greenland ice sheet in snowfall. These sulphates reduce the steadiness of the ice and favour the formation of microfissures.
A 2,700-metre borehole within the ice
The researchers discovered the ice quakes using a fibre-optic cable that was inserted right into a 2,700-metre-deep borehole and recorded seismic data from inside an enormous ice stream for the primary time. This borehole was drilled into the ice by researchers from the East Greenland Ice-core Project (EastGRIP), led by the Niels Bohr Institute and strongly supported by the Alfred Wegener Institute, leading to the extraction of a 2,700-metre-long ice core. Once drilling work was complete, the researchers took the chance to lower a fibre-optic cable 1,500 metres into the borehole and record signals from contained in the ice stream repeatedly for 14 hours.
The research station and borehole are positioned on the North East Greenland Ice Stream (NEGIS), around 400 kilometres from the coast. The NEGIS is the most important ice stream of the Greenland ice sheet, whose retreat is a big contributor to current rising sea levels. In the realm of the research station, the ice is moving towards the ocean at a speed of around 50 metres per yr.
As ice quakes occur continuously over a large area within the researchers’ measurements, ETH researcher Fichtner believes additionally it is plausible that they occur in ice streams in all places, on a regular basis. To confirm this, nonetheless, it would be mandatory to take seismic measurements of this type in other boreholes — and there are already plans to do exactly that.
