As part of a NASA-funded project called Arctic Transitions, WHOI researchers analyzed lake sediment cores dating back several thousand years to reconstruct the history of plant growth around two Arctic lakes. They found that when sea ice decreased and storms became more prevalent during warm periods in the past, there was an associated increase in erosion—as expected—but that increase slowed down or stopped when shrubs began to grow.
"Shrubs can bind sediments together and provide stability to the land," said the study's lead author, Breanyn MacInnes, a former postdoctoral researcher at WHOI and now a postdoctoral fellow at the University of Northern British Columbia. "As we see changes in climate and a lengthening of the shrub growing season, it is possible that shrub growth may mitigate some of the erosion that results from sea ice loss."
The findings, published online Sept. 1, 2022, in Scientific Reports, suggest that increased shrub growth may provide a natural defense mechanism for Arctic coasts facing more erosion and increased wave exposure and could provide coastal managers and communities with another adaptation tool to consider.
"Coastal erosion is a significant problem in the Arctic that threatens coastal communities, infrastructure, and ecosystems, but it is one that we don't fully understand," said co-author Woods Hole Research Center scientist Dr. Chris Maio, who was previously at WHOI. "This study provides a long term look at how shrubs may provide coastal protection, which may give us time to plan and adapt to future change."
The erosion of Arctic coastlines has accelerated dramatically in recent decades as the Arctic climate warms at a faster rate than the rest of the planet. The loss of sea ice and the increase in large waves during open-water periods have stripped away sediment from beaches and coastal cliffs once protected by ice.
Previous studies have shown that when sea ice melts farther from shore, waves can travel greater distances and carry higher amounts of energy, potentially resulting in more coastal erosion. However, the processes that can counteract these erosional forces have been less clear.
To investigate this question, the researchers collected sediment cores from two lakes located 20 kilometers (12 miles) apart in the Utqiagvik (formerly Barrow) area on Alaska's North Slope: Imnavait Creek Lake, located about a mile from the Beaufort Sea, and Imikpuk Lake, which is about 20 kilometers (12 miles) inland.
They then used a variety of geochemical and ecological techniques to analyze the cores, including radiocarbon and pollen analyses. These lake sediment records document changes that have occurred in the coastal watershed, including the timing of shrub expansion, sea ice, and storm activity.
The lake-sediment cores from both Imnavait Creek Lake and Imikpuk Lake revealed that the expansion of tundra shrubs occurred over the past 70 to 100 years in both drainages. This shrub expansion followed the expansion of lake-outlet deltas (sediment plumes in front of river mouths) and increased erosion from nearby coastal landscapes caused by increased storminess and loss of sea ice cover.
"The lakes provide an integrated record of what's happening in their watersheds, and that includes changes occurring on the coast 12 to 20 kilometers (7 to 12 miles) away," said MacInnes.
For example, at Imnavait Creek Lake, the record of increased erosion associated with delta expansion and less sea ice occurred over a period of several hundred years. At Imikpuk Lake, the record of increased erosion associated with increased storminess occurred over a period of about 150 years. In either case, the increased erosion was followed by increasing shrub growth.
"While erosion rates and increased shrub growth in these watersheds may be relatively slow processes when considered over centuries, they are remarkable for the fact that in the past 100 years, erosion increased and was counteracted by shrub growth within a human lifetime," said MacInnes.
For Arctic communities trying to adapt to the effects of climate change on coastal erosion, the study's lead author suggests that the potential protective role of shrubs is a natural attribute that should be considered when developing coastal protection measures.
"By understanding how shrubs may naturally mitigate erosion, coastal managers can make more informed decisions about how to adapt to the changing Arctic coastal system," said MacInnes.
