Association of Polar Early Career Scientists

 

Now, more than ever, it is important to constrain past glacier movements so that we can predict how modern glaciers will respond to current and future global warming. Due to the diminishing extent of sea ice each year and a series of positive feedback loops, the Arctic is experiencing amplified warming compared to the rest of the globe. Therefore, constraining the past movements of glaciers is even more important in these areas. Surface exposure dating is a versatile geochemical method that has expanded the geologist’s ‘toolbox’, allowing ages of past glacial movements that occurred thousands of years ago to be known. If we know how the glaciers were responding to different climates at those times, this helps us understand what will happen as our climate changes. Exposure dating tells us how long a particular material has been exposed to cosmic rays bombarding Earth, and can be done on both glacial landforms left behind by both the Greenland Ice Sheet and valley glaciers, both reservoirs of ice that will contribute to global sea level rise.

During my graduate work, I have had the opportunity to conduct exposure dating on boulders left by both glaciers and ice sheets in the past. During the summer of 2015 I traveled to the Petermann Glacier in Northwest Greenland to collect rock samples that will give us an indication of how it and the contributing Greenland Ice Sheet has been retreating over the past 10,000 years. Lateral moraines are sinuous ridged hills composed of boulders and glacial material that run alongside, parallel, to the glacier. They represent a time with the glacier was larger, wider in this case, for that hill to be right next to the glacial ice. Today, this lateral moraine is located 25 m away from the glacier, stretching 5 km alongside the glacier. We collected pieces of the uppermost surface of boulders along this moraine, selecting only boulders that fit our sampling criteria. We are looking for boulders located on the ridge of the moraine that are fairly large, usually ~1 m3, and that are composed of a non-local rock type. Washington Land and Daugaard-Jensen Land are composed of carbonate bedrock; formations of limestone, dolomite, and other rocks formed in deep marine waters. Carbonate rocks do not contain the mineral quartz, which is our target for this type of cosmogenic surface exposure dating. Therefore, we sampled primarily granite and sandstone boulders, which contain enough quartz for our analysis. By targeting non-carbonate boulders, we can be sure that the Petermann Glacier transported the rocks from a location in the interior of Greenland before being deposited on the lateral moraine.

Once we returned to the University of Wisconsin-Madison, we crushed each rock sample to sand size, and isolate the quartz minerals using magnets and density separation methods. Next we use strong acids such as hydrofluoric and hydrochloric acids to dissolve the quartz into a clear solution. The final steps require isolating the Be from all the other elements present in the quartz. Finally, we oxidize the Be and send it to an accelerated mass spectrometer to be measured. Once we have all the results, we can calculate the time that specific boulder was exposed to the atmosphere, interpreting this time as how long ago the glacier left the boulder on the landscape. Combined with results from the other boulders, we can understand how old the lateral moraines are. The age of the moraine might represent a climate event that could be reflected in the sediment cores collected by collaborating research groups investigating the paleoclimate history of the Petermann Glacier using marine fauna.

Liz Ceperly blog

Photo: Trek to the Petermann Glacier

Contact APECS

APECS International Directorate
UiT The Arctic University of Norway
Huginbakken 14
9019 Tromsø
Norway
Email: info(at)apecs.is

Our Sponsors

APECS Directorate Sponsor
 
UiTNPIFRAM
 
Further Sponsors and Partners for APECS projects, activities and events