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Barrier islands and spits shelter coastlines from storms, protecting coastal communities and providing habitat for native species.

Polar bear appears to walk on top of rippled gray water. Just behind it are very large breaking waves below a gray-blue sky.
Adult polar bear walking across a recently overwashed barrier island during a large Arctic storm in September 2016. The barrier island is offshore of Barter Island on Alaska’s north coast. Polar bears typically rest on the barrier islands during the day and transit to the "bone pile" on Barter Island in the evenings to feast on whale carcass remnants supplied by local village whaling activities. USGS scientists study coastal change on Alaska’s north coast.

Barrier islands and spits shelter coastlines from storms, protecting coastal communities and providing habitat for native species. Formed under a variety of conditions, barrier islands are themselves highly variable, often changing in shape from season to season, year to year.

This is nowhere more apparent than in the Arctic, where barriers are subject to seasonal shifts in sea ice and permafrost during the brief Arctic summer–shifts that are becoming more pronounced with climate change. 


A new report from USGS researchers at the Pacific Coastal and Marine Science Center and collaborators tracks how barriers along Alaska’s North Slope have changed from 1947 to 2020, pulling from a variety of data sources including satellite imagery, past climatological records and LIDAR (“light detection and ranging”) scans of the coastline.  The report is titled, “Assessment of barrier island morphological change in northern Alaska.”

The report finds that over the past 50 years, barrier islands along the Alaskan Arctic coast have decreased in number but increased in area, possibly due to changes in wave behavior and sediment supply. As sea ice retreats and permafrost thaws under a warming climate, high winds, waves and freshwater currents can further destabilize these barriers. 

Photo from an airplane looking down at a very flat, low island surrounded by ocean.
Photograph of Pingok Island, Alaska, reveals physical features of a changing Arctic: collapsing bluffs, salt-killed tundra (lighter brown near the bluff edge), and drained thermokarst lakes (rust-colored depressions).

“This work is impressive in that it shows how dynamic Arctic barriers truly are,” said Jennifer Miselis, a research geologist at the USGS St. Petersburg Coastal and Marine Science Center who was not involved with the report. “By studying how barriers change in the compressed time scales at Arctic latitudes—where waters are ice-free for just three months a year—w e can potentially use them as analogs to study how barriers elsewhere will respond to climate change.” 


Barrier islands stretch across approximately 50 percent of Arctic Alaska’s coast. Besides serving as a physical barrier against storms, these islands are used as resting and nesting habitat by birds, denning habitat for polar bears, and haul-out areas for walruses. They support energy and defense-related infrastructure on the North Slope and are home to Alaska Native villages and subsistence hunting camps. 

“Understanding the drivers of the change we’re seeing on these barrier islands is a challenge because there isn’t much observational or oceanographic data available along this remote coast. Basic information on things like the materials that comprise Arctic barriers and how their sediments are eroded and deposited are also lacking,” said Ann Gibbs, a USGS geologist and an author of the report. “However, with potential threats to coastal habitat, infrastructure, and Alaska Native communities associated with climate change, there is an urgent need for better understanding of the rates and drivers of barrier island change as well as for improved predictive modeling of future island conditions.”

Learn more about the USGS project, “Climate impacts to Arctic coasts.”

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