Greenland sits over an area of abnormally hot mantle material that drives a widespread melting beneath the ice sheet and rapid ice flow over a distance of several hundred kilometres, a new study has found. Greenland’s lithosphere has hot depths which originate in its distant geological past and cause the island's ice to rapidly flow and melt from below. An anomaly zone crosses Greenland from west to east where present-day flow of heat from the Earth’s interior is elevated.
With this anomaly, researchers from GFZ German Research Centre for Geosciences (GFZ) could explain observations from radar and ice core drilling data that indicate a widespread melting beneath the ice sheet and increased sliding at the base of the ice that drives the rapid ice flow over a distance of 750 kilometres from the summit area of the Greenland ice sheet to the North Atlantic Ocean.
The North Atlantic Ocean is an area of active plate tectonics. Between 80 and 35 million years ago tectonic processes moved Greenland over an area of abnormally hot mantle material that still today is responsible for the volcanic activity of Iceland, researchers said.
The mantle material heated and thinned Greenland at depth producing a strong geothermal anomaly that spans a quarter of the land area of Greenland, they said. This ancient and long-lived source of heat has created a region where subglacial meltwater is abundant, lubricating the base of the ice and making it flow rapidly.
The study indicates that about a half of the ice in north-central Greenland is resting on a thawed bed and that the meltwater is routed to the ocean through a dense hydrological network beneath the ice. For the first time, researchers have been able to prove strong coupling between processes deep in the Earth’s interior with the flow dynamics and subglacial hydrology of large ice sheets.
“The geothermal anomaly which resulted from the Icelandic mantle-plume tens of millions of years ago is an important motor for today’s hydrology under the ice sheet and for the high flow-rate of the ice,” said Irina Rogozhina from GHZ.
“This, in turn, broadly influences the dynamic behaviour of ice masses and must be included in studies of the future response to climate change,” said Rogozhina. The location and orientation of the zone of elevated geothermal heat flow shows where Greenland moved over the Iceland mantle plume, researchers said.
This unexpected link between hotspot history and ice sheet behaviour shows that the influences on ice sheets span a huge range of timescales from the month by month changes of the ice cover to the multi-million year epochs over which the Earth’s mantle and tectonic plates evolve, they said. The findings were published in the journal Nature Geoscience.