Baffin Island in Nunavut, Canada, has served as the backdrop for dozens of investigations into glaciation and ice-age patterns. Now a new paper takes a unique look at assigning ages to some of the oldest moraines from the most recent episode of glacier expansion in the Canadian Arctic.
Moraines, ridges of debris deposited alongside or in front of a glacier, can contain valuable data for understanding past climate. The positions of these debris are controlled by temperature and precipitation, which when combined with moraine dating can help construct a picture of past glacier margins. Ice-cored moraines fronting debris-covered glaciers, like the ones this paper investigated, are formed when glaciers with debris on them, like rocks and sediment, retreat and leave behind sections of debris-covered ice. Over time, that ice slowly melts— and its melt-rate is affected (often further slowed) by all the debris that cover and protect the ice from solar radiation. These ice-cored moraines, named because they are moraines with remnants of glacial ice, are notoriously difficult to study because there are many factors that influence how accurately they can be dated. Fully extrapolating the glaciers’ positions and age from the ice-cored moraines also depends on the long history of temperature and precipitation in the area, which contributes to glacier formation and melting. However, when all these factors are accounted for, the positions of these debris can show the location of past glacier margins, reflecting the size of glaciers in the past.
To date the moraines, the researchers examine the concentration of a beryllium isotope, 10Be, that accumulates only in some minerals (like quartz) in the uppermost layers of rocks. The rate of accumulation is well understood and based on cosmic ray interactions in the atmosphere and within the rock itself. Since only rocks on the earth’s surface accumulate 10Be, researchers can calculate how long that rock was exposed on the earth’s surface by comparing the concentrations of isolating a sample of 10Be in a rock from a moraine to other well-dated rocks. GlacierHub spoke with Sarah Crump, the lead author on this paper, who explained that with this information “we can estimate when a glacier was extended to the location of the moraine, and thereby make inferences about climate at the time.” Using this data, they reported that the moraines likely formed5,200 to 3,500 years ago during the Neoglaciation of the Late Holocene.
However, 10Be dating has some uncertainty. Crump and her team realized that because “the 10Be ages exhibited quite a bit of spread,” they needed to take a closer look at the glacial setting and mechanics of moraine formation. “We thus teamed up with co-author Leif Anderson to collect glaciological data at the field sites and model a simplified, representative debris-covered glacier,” she said. Additionally, they used field observations of the moraines to decipher if the debris had evolved since their initial formation. The researchers looked for evidence of morphological changes caused by uneven ice melting over time, or moraine degradation leading to surface boulders to roll and new boulder faces to emerge— all of which can affect 10Be dates. The results of the paper combine findings from these three methods: 10Be dating (or more formally cosmogenic radionuclide dating), numerical modeling based on field collected glaciological data, and field observations for moraine evolution.
Due to this collaboration and methodology, this study is unique. Michael Kaplan, a paleoclimatologist at Columbia University, commented on the novelty of this research: “I am not familiar with another paper that uses these three approaches (and the different respective experts as coauthors) in the manner that Crump et al. do.”
Though this combination of methods is novel, Crump stated that there are still some uncertainties in the precise formation age of the moraines. Often, 10Be dating results can deliver ages that are either older or younger than the actual age of the moraines. For example, rocks and boulders that ended up on a moraine might have arrived before glacial erosion, which would result in an age that was too old. The other two methods— field observations and numerical modeling— helped inform their final conclusions and significantly reduced uncertainty (though some uncertainty inherent to 10Be dating can never be completely eliminated).
Overall, Crump hopes that “readers will take note of the very important role of debris in glacier systems, both in terms of how they respond to climate variability and in terms of their geomorphic effect on the landscape.” These results show the importance of taking into account the glacial setting and help to clarify and identify some of the uncertainty around the moraine record, giving a deeper understanding of the relationship between glacier fluctuation and climate variability, allowing researchers to gather more detailed and accurate information about past climates and therefore better assess the future.
If you’re interested in learning more about the area, Gifford Miller, a co-author of the paper has an informative video about Baffin Island and its importance.