Cooperative Institute for Research in Environmental Sciences

Thawing Alaska

Summer 2008

Drew Point's Unique Landscape

The fine silts near Drew Point make this area of Alaska's northern coastline especially susceptible to erosion. Eroded blocks of land literally melt away in the Beaufort Sea -- their fine-grained silts carried away in suspension rather than settling in place to protect the coast from future wave action. The region is also composed of permafrost, which means that the bluffs are permanently frozen and held together by ice. Warming temperatures put this region at risk of continued erosion as the permafrost thaws.

Perils of Permafrost

Permafrost is soil, sediment, or rock that remains at 0°C – freezing – or below for at least two years. About 23 million square kilometers of the Northern Hemisphere are composed entirely or in part of permafrost. The permafrost layer, which can range in thickness from centimeters to more than 1,000 meters, may contain a large amount of ice or virtually no ice at all.

Seasonal changes in temperature can affect the uppermost few meters of permafrost, creating an “active layer” that seasonally thaws and freezes above the permafrost. In addition, longer timescale “secular” changes in surface temperatures can penetrate to tens of meters depth, and these changes record extended periods of climatic warming. Temperature data has been collected from boreholes drilled into the Alaskan coastal plain beginning in the 1980s. Using repeated monitoring of these sub-surface temperature profiles over the last 30 years, scientists have documented increases in permafrost temperatures all along Alaska's North Slope.

Thawing permafrost poses several concerns. First, it undermines the structural stability of the ground, which can threaten buildings, roads, and other infrastructure in developed areas. Second, it releases carbon into the atmosphere, contributing to the human-made greenhouse effect.

Sea Temperatures and Shrinking Sea Ice

Every year Arctic sea ice recedes during the sunny months of summer and advances during the long, dark winter. However, scientists have observed an alarming shrinking trend in the minimum extent of Arctic sea ice. Through 2007, the September decline now exceeds 10 percent per decade. Scientists at the National Snow and Ice Data Center worry that by 2030-2050, sea ice may no longer exist during the Arctic summer.

As sea ice recedes, it reveals dark ocean water, which absorbs solar energy far more effectively than white, reflective ice. By absorbing additional sunlight, the ocean itself warms and also heats the atmosphere above. The warmer ocean and air temperatures then facilitate the melting of more ice, which in turn exposes more of the dark ocean to the sun’s heat – a strong positive feedback.

As the ocean warms, it also transfers some of its heat energy to the coastline, thawing the ice that holds the coastal bluffs together. Even in the absence of storms, the bluffs are melted along their base by warming seawater, eventually becoming destabilized and toppling into the sea. Erosion rates as high as 30 meters (100 feet) per year have been observed near Drew Point, Alaska.

Wave Action

This melting and destabilizing of coastal bluffs is likely to be one of the most important cause of higher erosion rates, but other factors are also at play. As Arctic sea ice recedes, it also creates greater expanses of open water, or fetch. Larger fetch provides more room for winds to create waves during storm events. As a result, the shrinking sea ice may also be responsible for increasing the intensity of erosion due to coastal battering by waves.

What's at Risk?

High erosion rates create a landscape in dramatic change, and this has consequences for the natural ecosystem, cultural sites, and the built environment. Drew Point, Alaska is located within a special protected wildlife habitat called the Teshekpuk Lake Special Area (TLSA). The TLSA is the summer home for dozens of species of migratory birds, who come from as far away as Mexico to raise their young. As the coastline recedes, the lakes that these birds call home are being drained into the sea, shrinking the habitat these birds depend on.

The coast of Alaska also has special historical significance. Inupiat cultural sites including hunting camps, fishing camps and trading posts are spread along the TLSA coastline, and many of these are being lost to coastal erosion.

Finally, thawing permafrost and coastal erosion threatens much of the petroleum infrastructure along the North Slope of Alaska, including test wells within the TLSA and developed sites further to the east. Understanding what controls coastal erosion rates is therefore crucial for predicting where and when existing and planned coastal development may be vulnerable in the future.