Over the last several millions of years, the Greenland ice sheet has experienced periods of dramatic growth and shrinkage in response to climate change cyclicity. This growth and shrinkage are recorded in the sediments deposited by large ice streams on the continental margin of Greenland.
Using a dense grid of seismic reflection data, the scientists have carried out a detailed mapping of sediments deposited by glaciers along the northwest Greenland shelf where two of the largest glacial outlets, so called trough-mouth fans, have drained the ice sheet. This mapping shows that 11 major phases of ice sheet advance have occurred over the shelf margin during the last 2.7 millions of years, with each cycle lasting between 200,000 and 400,000 years. Importantly, the data show that the ice sheet advances have changed over time indicating variations in glacial dynamics.
At around 1 million years ago, the ice advance pattern changed from a uniform flow across a wide part of the shelf margin to erosive ice streams that focused sediment delivery through the present day troughs. This transition correlates to a time in Earth's climate history when glacial variability changed from a dominantly 40,000 year cycle to a 100,000 year cycle. This suggests that the Greenland ice sheet plays a role in this important climate transition.
Core drillings will provide scientists with 30 million year old climate data
“Coupling our observations of shelf margin sedimentation with ice sheet modelling can raise our understanding of how large ice streams initiate and decay. Modern ice streams in Greenland and Antarctica form major sources of icebergs and meltwater, so a better understanding of their stability thresholds and boundary conditions is important for predicting increases in sea-level as a result of global warming,” says Paul Knutz, senior scientist at GEUS.
There are ongoing efforts to retrieve long-term sedimentary archives that can shed new light on the history of the Greenland ice sheet. One of the main questions is how the ice sheet responded during periods of relatively warm climate conditions equivalent to the 'Anthropogenic' scenario we are currently experiencing.
“Together with an international group of scientists, we are planning for scientific drillings on the West Greenland shelf margin that can provide us with a climate record going 20-30 million years back in time. To achieve this, we are proposing to use the drilling vessel Joides Resolution operated by the International Ocean Discovery Programme. This mission could become real in 2022 but already this summer we will be collecting more data in the northeast Baffin Bay using the Danish naval vessel Lauge Koch,” says Paul Knutz.