The rate of coastal erosion more than doubled in Alaska—to as much as 45 feet per year—within the 52-year period between 1955 and 2007 along a 37-mile stretch of the Beaufort Sea, with ice-rich coastal bluffs showing the greatest increase in recent erosion rates.
A study led by the U.S. Geological Survey (USGS) Alaska Science Center reveals that average annual erosion rates along this part of the Beaufort Sea—north of a large lake named Teshekpuk and about 100 mi west-northwest of Prudhoe Bay—climbed from historical levels of about 20 feet per year between the mid-1950s and late-1970s, to 28 feet per year between the late-1970s and early 2000s, to 45 feet per year between 2002 and 2007. The authors also observed that spatial patterns of erosion have become more uniform across shorelines with different degrees of ice richness. Until 2002, erosion rates were highest on shorelines with relatively low ground-ice content; but from 2002 to 2007, the greatest increase in erosion rates occurred for ice-rich terrain, suggesting a fundamental shift in the dominant processes driving and resisting erosion. The study was published in Geophysical Research Letters, a publication of the American Geophysical Union.
The authors propose that the shifts in the rate and pattern of land loss along this segment of coastline are likely the result of changing Arctic conditions, including declining sea-ice extent, increasing summertime sea-surface temperature, rising sea level, and increases in storm power and corresponding wave action.
"Taken together, these factors may be leading to a new regime of ocean-land interactions that are repositioning and reshaping the Arctic coastline," wrote USGS research geographer and lead author Benjamin Jones and his colleagues. The authors noted that any increase in the current rates of coastal retreat will have further ramifications for Arctic landscapes—including impacts on important freshwater and terrestrial wildlife habitats and subsistence grounds for local communities, possible effects on the global carbon budget through the release of organic carbon previously frozen in permafrost, adverse impacts on coastal villages and towns, threats to resource-extraction infrastructure (one test well has already been lost), and the loss of cultural sites that provide a record of human settlement in the Arctic.
In another recent study along the same stretch of the Beaufort Sea, Jones and his coauthors verified "disappearing" cultural and historical sites, including Esook, a hundred-year-old trading post now underwater on the Beaufort Sea floor, and Kolovik (Qalluvik), an abandoned Inupiaq village site that may soon be lost. At another site, near Lonely, Alaska, Jones snapped a picture of a wooden whaling boat that had rested on a bluff overhanging the ocean for nearly a century. A few months later, the boat had been washed away to sea. This study was published in the December 2008 issue of the journal Arctic.
Arctic climate change is leading to rapid and complex environmental responses in both terrestrial and marine ecosystems that will almost certainly affect the rate and pattern of Arctic coastline erosion. "For example," said Jones, "the recent trends toward warming sea-surface temperatures and rising sea-level may act to weaken the permafrost-dominated coastline through preferential thaw of extremely ice-rich coastal bluffs, and may potentially explain the disproportionate increase in erosion along ice-rich coastal bluffs relative to ice-poor coastal bluffs that we documented in our study."
The authors also documented sections of coastline that eroded more than 80 ft during 2007. Interestingly, summer 2007 had no westerly storms, traditionally believed to be the drivers of coastal erosion in this region of the Arctic; however, 2007 did have the lowest Arctic sea-ice extent on record and relatively warm ocean temperatures.
"Erosion of coastlines is a natural process," said Jones, "and this segment of coastline has historically eroded at some of the highest rates in the circum-Arctic, and so the changes occurring on this open-ocean coast might not be occurring in other Arctic coastal settings." Shoreline change along the entire U.S. Beaufort Sea coast is currently being investigated by another USGS team headed by geologists Bruce Richmond and Ann Gibbs of the USGS Pacific Science Center in Santa Cruz, California, as part of a multiyear assessment of shoreline erosion and accretion along all U.S. coastlines (see "The Shrinking Beaufort Sea Coastline," this issue). Richmond and Gibbs began studying the Beaufort Sea coast in 2006 by collecting oblique aerial photographs and video footage from a small floatplane (see "North to Alaska—an Aerial Shoreline Reconnaissance" in Sound Waves, October 2006). The imagery collected during that reconnaissance study was recently published as USGS Data Series 436. Richmond and Gibbs are now analyzing historical maps and photographs of the Beaufort Sea coast and digitizing the data in a consistent format that will allow comparison with data from future surveys, as well as from other U.S. coastlines. Preliminary results suggest that erosion in the Prudhoe Bay area has also been accelerating but at a much slower rate than the erosion documented north of Teshekpuk Lake by Jones and his colleagues.
Jones, Richmond, and Gibbs will all be working along Alaska's Arctic coast this summer, as will coastal engineer Li Erikson, currently a USGS Mendenhall Postdoctoral Research Fellow at the USGS Pacific Science Center. Richmond and Gibbs will work with a team that is collecting airborne-lidar (light detection and ranging) land-elevation data that can be used to document the position of the modern shoreline and to estimate the input of sediment and organic carbon as a result of rapid erosion along the Beaufort Sea coast. Jones and others from the Alaska Science Center will continue collecting ground-based data, some of which will provide control points for the airborne-lidar data. Erikson will initiate a focused physical-processes and modeling study on the Chukchi Sea coast between Barrow and Wainwright to better understand the primary factors driving coastal change in the Arctic. She will collect wave, current, salinity, and temperature measurements near the seabed in about 10 m of water at two sites; and bathymetry, sediment grain size in the nearshore and on the shoreface, and various material properties of the bluffs at selected areas within the region. The data she collects are anticipated to provide insight into the processes controlling coastal erosion, to serve as calibration and validation data for hydrodynamic and morphodynamic modeling, and to be a baseline for future studies. The researchers will share their data to help build a comprehensive picture of Arctic shoreline erosion and its causes.
In their recent report, Jones and his coauthors emphasize that scientists should continue monitoring to better understand the causes of the increased coastline erosion they documented. The paper, "Increase in the Rate and Uniformity of Coastline Erosion in Arctic Alaska," was authored by B.M. Jones (USGS), C.D. Arp (USGS), M.T. Jorgenson (ABR, Inc.), K.M. Hinkel (University of Cincinnati), J.A. Schmutz (USGS), and P.L. Flint (USGS) and published in the February 14, 2009, issue of Geophysical Research Letters. To read more about the loss of cultural and historical sites along this coastal segment, see the December 2008 issue of Arctic (v. 61, no. 4, p. 361-372, URL http://www.arctic.ucalgary.ca/index.php?page=arctic_contents). That paper,"Modern Erosion Rates and Loss of Coastal Features and Sites, Beaufort Sea coast, Alaska," was authored by B.M. Jones (USGS), K.M. Hinkel (University of Cincinnati), C.D. Arp (USGS), and W.R. Eisner (University of Cincinnati).
in this issue:
Erosion Doubles Along Alaska's Arctic Coast