Climate change 'secrets' recovered from bottom of Greenland lake

Climate change 'secrets' recovered from bottom of Greenland lake

Scientists from the University of Aberdeen have delved to the bottom of an arctic lake in order to chart the effects of climate change over the past 10,000 years in an effort to better understand global warming.

Earlier this month, a team of geoscientists travelled to a glacier beyond the margins of the Greenland ice sheet to retrieve samples from the bed of a glacier-fed lake which is ice-free only during the summer months.

By analysing the sediment from the lake, the team, which included scientists from the University of Bergen, hope to understand how the glacier which feeds the lake has behaved in the past, which will give an indication of what the climate was like thousands of years ago.

Researcher and project leader, Craig Frew said: “There are less than 100 years of detailed observations of climate available on a global scale, so to reconstruct a more comprehensive timeline of change over thousands of years, one of the things we can look at are proxy records of glacier variability.

“These help us to put the contemporary warming trend into a longer context to try and understand how sensitive the area is and how temperature and precipitation have changed according to climatic forcing.

“The past is a key to understanding the future. To have confidence in climate models that are designed to predict future climate we have to be able to test and constrain them using instrumental or proxy records.”

East Greenland in a nutshell by Willem van der Bilt 

The team travelled to an island called Ammassalik in southeast Greenland, and retrieved the samples by taking a small raft onto the lake and lowering a piston corer around 20m to the lake bed, where a 6m long PVC tube was hammered in to retrieve a ‘core’ of material.

Taking care not to disturb the samples, the cores were shipped to Bergen by boat for radiocarbon dating and other analyses.

Craig added: “By looking at the sediment eroded by the glacier and deposited in the lake we can see how much organic material there is and how the grain size changes. We can measure the different elements present, such as iron and titanium, and this helps us to understand how the glacier has behaved in the past, and that can give us a better understanding of what the climate was like and how it has fluctuated over long periods of time.

“Chironomids (non-biting midges) preserved within the samples give an indication of past temperatures. We can also look at different isotopic biogeochemical proxies to gain a better understanding of the water balance and the hydrological cycle.

“The Greenland Ice Sheet is a massive body of ice, it takes a relatively long time to respond to climate change, and it is difficult to study. Smaller glaciers such as the one at Ammassalik are much more sensitive. They allow us to look at how climate has changed in the past through the response of the glacier. In turn, this may help us to develop a better picture of how the Greenland Ice Sheet might have reacted over the same period.

“That feeds into important discussions we’re having right now about increased mass loss from the Greenland Ice Sheet and the impact that will have on sea level change. The climate has varied over the past 10,000 years and there have been times that were warmer and colder than present. What we need to do is understand what the climate system is doing and how this part of the world responds and how the glaciers react to this.”

The five-strong team consisted of Craig, Dr Matteo Spagnolo and Dr Brice Rea from the University of Aberdeen, plus two PhD students from the University of Bergen, Willem van der Bilt and Torgeir Rothe.

The project is funded by the EU Network ‘INTERACT’ and Craig’s PhD is funded by the University of Aberdeen’s ‘The North’ strategic research theme.