Huge ice currents transport ice from Germany to the ocean in Greenland and contribute considerably to the increase in sea level. Previous simulations assumed that the ice currents will flow slowly and steadily like tough honey – but they only inadequate reality. A study now shows that countless small quakes jerked the ice current. The quake assumes contaminants in the ice that come from particles of earlier volcanic eruptions. The findings help to better understand the dynamics of the ice flows and thus predict the future increase in sea level more precisely.
In Greenland, huge amounts of ice cream transport large amounts of ice from domestic to the ocean. The largest ice current alone, the “Northeast Greenland Icestream” (Negis), which moves the ice at a speed of around 50 meters per year, is responsible for around twelve percent of the total mass outflow of the Greenland ice shield. He contributes significantly to the increase in sea level. In order to understand the movements of these currents and estimate their mass loss, glaziologists use computer simulations. So far, they assumed that the ice currents behave honey and slowly but steadily. However, these simulations were insufficiently matching satellite measurements of the flow speed.
Bohrloch on the largest ice current in Greenland
A team led by Andreas Fichtner from ETH Zurich has now found an explanation for the deviations between simulations and satellite data: deep inside the ice currents there are always tiny quakes that trigger each other and drive the ice current. “The assumption that ice flows flow only like tough honey is no longer durable,” says Fichtner. “They also move through a constant jerking.” For their investigations, Fichtner and his team used a borehole on the Negis, from which a 2700 meter long ice drilling core was taken for another research project. The researchers downloaded a 1500 -meter -long fiber optic cable into this borehole, with which they marked the seismic activities for 14 hours at a time.
The measurements actually detected shocks in the depth of the ice current: “The records contain five clear seismic events,” reports the research team. “Some of these consist of over 100 lower events that follow the cascade like a cascade.” These small, but significant ice creamquakes cannot be observed on the surface. As Fichtner and his team found, the spread of the quake stops around 900 meters below the surface of the ice. The comparison with the ice drilling nucleus removed from the hole shows: Here is a layer of volcanic particles that come from Mount Mazama’s outbreak in today’s Oregon in the USA 7700 years ago.
Historical volcanic eruptions influence ice dynamics
“We were very amazed at the previously unknown connection between the dynamics of an ice stream and volcanic eruptions,” says Fichtner. Apparently, the volcanic particles in the ice influence the spread of vibrations in the ice. However, the influence of earlier volcanic eruptions is even enough: the researchers found that the polar belly of contaminants in the ice stream, which were caused by further volcanic eruptions in other parts of the world. In the case of volcanic eruptions, Sulfate comes into the atmosphere, some of which were deposited with the snow in Greenland. This sulfate then ensures increased flow resistance deep in the ice shield and create tensions. These help to form tiny cracks – which can eventually become the starting point for the polar objects.
The researchers assume that the knowledge can improve future simulations of ice current and thus lead to more precise forecasts to change the sea level. Based on their observations on the largest ice current in Greenland, they think it is plausible that ice creamquakes also play a role for other ice currents. In future studies you want to check this with further seismic measurements in other boreholes.
Source: Andreas Fichtner (ETH Zurich, Switzerland) et al., Science, Doi: 10.1126/science.adp8094