Perennial Snowfields of the Central Brooks Range: Valuable Park Resources

By Molly E. Tedesche, International Arctic Research Center, University of Alaska Fairbanks and Jeffrey T. Rasic, National Park Service

Thousands of years ago, snow and ice in the central Brooks Range of Arctic Alaska might have looked very different than it does today. Glaciers and perennial snowfields (also known as snow patches or ice patches) in what is now Gates of the Arctic National Park and Preserve (Figure 1) were probably much more extensive then than they are now. Perennial snowfields, like glaciers, are masses of snow and ice that persist for many years and form through the accumulation and compaction of snow. However, unlike glaciers, snowfields never grow thick enough to flow with gravity. In modern times, as in the past, caribou herds move to these snowfields in the summer to stay cool and avoid insects (Anderson and Nilssen 1998). Perennial snowfields are also important ecosystems for an array of different bird species (Rosvold 2016). They influence water availability for down-slope vegetation (Lewkowicz and Young 1990) and alter geology (Berrisford 1991) and permafrost (Luetschg et al. 2004).

Figure 1. Gates of the Arctic National Park and Preserve

Perennial snowfields are an important component of Arctic parks in Alaska, but with pronounced warming (Johannessen et al. 2004, Hinzman et al. 2005), the Arctic is shifting rapidly, and these snowfields are retreating. Snowfields are relatively small and sensitive to climate change (Figure 2), and reductions in year-round ice extent have been evident in the Brooks Range during the late 20^th century (Evison et al. 1996).

Their loss also has the potential to reveal well-preserved archaeological artifacts or ancient animal remains with significant cultural value. Such discoveries have been made in the last decade in snowfields in the southern Yukon (Alix et al. 2012, Hare et al. 2012) and Northwest Territories (Meulendyk et al. 2012) of Canada, and in Wrangell-St. Elias National Park and Preserve (Dixon et al. 2005). Archaeologists think that ancient caribou herds used snowfields in a manner similar to modern herds for insect relief, where ancient hunters tracked them, and sometimes left behind weapons and other tools that became frozen in ice.

Figure 2. Small perennial snowfield in the central Brooks Range, Alaska shows signs of retreat.

Courtesy of Rick Swisher

In the summer of 2015, we initiated a project to study the extent of changes to perennial snowfields in order to target archaeological field surveys. NPS researchers began by creating an extent model to map and classify individual snowfields by proximity to caribou, as a proxy for ancient herds (Figure 3).

This was done by combining caribou movement data from the Western Arctic Caribou Herd with a map of snow persistence based on Landsat satellite imagery for Northwest Alaska (Macander et al. 2015). Snowfields in close proximity to places frequented by caribou were then prioritized for field survey based on factors contributing to possible ease of access by ancient hunters, such as gentle slope angles of snowfields and the surrounding terrain.

Figure 3. Perennial snowfield extent map derived from Landsat imagery-based data, classified by proximities to caribou movements.

Ground-based and aerial surveys were then conducted to look for artifacts and investigate locations and extents of the snowfields (Figure 4). Seventeen snowfields and three glaciers were surveyed for geometry on foot using a GPS with high spatial resolution. Each site was characterized using snow test pits, ice auger bore holes, snow crystal structure and layering, and melt-water chemistry parameters.

We surveyed 160 snowfields by helicopter, and conducted visual evaluations for archaeological potential, and location agreement with the extent model. We collected hydrological and biological samples, including water samples, bird remains, and caribou bones and dung. Results of the fieldwork indicate agreement between modeled and surveyed locations of snowfields.

Figure 4. A helicopter assisted field survey of perennial snowfields in July of 2015 provided a much-needed opportunity to field validate the model.

Courtesy Molly Tedesche

During the 2015 study, no archaeological artifacts were discovered; however, we identified well-preserved animal remains (including soft tissue, skin and feathers) dating to up to 200 years ago. These materials can help reconstruct a record of ecological and biological change that provides context for understanding recently observed changes in the environment. Snow test pits and ice auger bore holes indicated that several of the perennial snowfields surveyed were between 0.74 and 2.23 meters deep, while several others were much deeper than the ice auger could bore or test pits could reasonably be dug. Chemistry indicated that the melt-water pH was neutral to quite acidic. These results establish a baseline for future perennial snowfield monitoring.

The nature of change in perennial snowfields in the central Brooks Range is one of rapid decline, and these changes are of increased significance to the high alpine hydrology and ecology of Gates of the Arctic. Ongoing work will build on the 2015 findings to quantify past perennial snowfield extent and create a snowfield taxonomy that categorizes snowfields with similar physical, topographic, and microclimatic characteristics to predict projected rates of change. Results of this research will help archaeologists continue to target field survey areas, as well as address the impacts that these changes are having on park resources, such as hydrology, vegetation, and wildlife.

Acknowledgements

Chris Ciancibelli, Adam Freeburg, and Kyle Joly were important in planning, field work, and analyses discussed in this article and their help is gratefully acknowledged.

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