The Cordilleran Ice Sheet covered the mountains of western Canada and its extent and ice volume were comparable to the present-day Greenland Ice Sheet. The study employed a technique called cosmogenic exposure dating, in which the amount of isotope 10Be, formed in the surface layers of rocks through cosmic radiation, is used to quantify the duration for which the rock surfaces have been exposed since they emerged from below the ice sheet.

A double-crested Tuya Lake moraine (centre of the photograph) marks a large outlet glacier that emanated from the central Cassiar Mountains during the Younger Dryas. Photo Julien Seguinot.

 

A double-crested Tuya Lake moraine (centre of the photograph) marks a large outlet glacier that emanated from the central Cassiar Mountains during the Younger Dryas. Photo Julien Seguinot.

Martin Margold, Arjen Stroeven, Julien Seguinot and Jakob Heyman provided 20 out of the 76 10Be deglaciation ages on moraine and glacial erratic boulders that the study authors collected from the landscapes formerly covered by the Cordilleran Ice Sheet.

Rapid thinning of the ice sheet and sea-level rise 

The new data indicate a rapid thinning of the ice sheet during the Bølling warming, a period starting at about 14.7 thousand years ago when climate warmed abruptly from the cold of the last ice age. The study makes use of two recently published glacio-isostatic adjustment models to reveal that the ice sheet might have lost up to half of its mass in as little as 500 years, causing 2.5 to 3.0 meters of sea-level rise.

The initial warming was followed by periods of colder climate that allowed for a re-growth of small glaciers in mountain areas that had just emerged from the ice sheet and a local reinvigoration of the ice sheet remnants. The complex pattern of ice sheet decay in montane environments reconstructed by the study calls for the use of sophisticated surface mass balance and ice dynamics models when the future of the Greenland Ice Sheet is being assessed.

Two doctoral theses and a number of research papers

The paper published in Science marked a successful completion of a project reconstructing the former Cordilleran Ice Sheet that the researchers at the Department of Physical Geography carried out for over ten years and which included two doctoral theses and a number of research papers in field-specific journals.

The paper in Science