30 November 2016
By Catherine Puckett
Permafrost loss due to a rapidly warming Alaska is leading to significant changes in the freshwater chemistry and hydrology of Alaska’s Yukon River Basin with potential global climate implications, a new study finds.
This is the first time a Yukon River study has been able to use long-term continuous water chemistry data to document hydrological changes over such an enormous geographic area and long time span.
The results of the study have global climate change implications because of the cascading effects of such dramatic chemical changes on freshwater, oceanic and high-latitude ecosystems, the carbon cycle and the rural communities that depend on fish and wildlife in Alaska’s iconic Yukon River Basin.
“As the climate gets warmer, the thawing permafrost not only enables the release of more greenhouse gases to the atmosphere, but our study shows that it also allows much more mineral-laden and nutrient-rich water to be transported to rivers, groundwater and eventually the Arctic Ocean,” said Ryan Toohey, a researcher at the Department of the Interior’s Alaska Climate Science Center in Anchorage and lead author of the new study. “Changes to the chemistry of the Arctic Ocean could lead to changes in currents and weather patterns worldwide.”
The new study was accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.
The Domino Effect
The Yukon River Basin, which is the size of California, starts in northwestern British Columbia, then flows northwest through Yukon across the interior of Alaska to its delta, where it discharges into the Bering Sea. Eventually, its waters reach the Arctic Ocean; it is one of six major rivers that play an important role in the circulation and chemical makeup of the Arctic Ocean.
The new study, which analyzed more than 30 years of data, sheds light on how climate change is already affecting this system. The study specifically found that the Yukon River and one of its major tributaries, the Tanana River, have experienced significant increases in calcium, magnesium and sulfate over the last three decades.
Permafrost rests below much of the surface of the Yukon River Basin, a silent store of thousands of years of frozen water, minerals, nutrients and contaminants. Above the permafrost is the active layer of soil that freezes and thaws each year. Aquatic ecosystems – and their plants and animals – depend on the ebb and flow of water through this active layer and its specific chemical composition of minerals and nutrients.
When permafrost thaws, the soil’s active layer expands and new pathways open for water to flow through different parts of the soil, bedrock and groundwater. These new pathways ultimately change the chemical composition of both surface water and groundwater.
As permafrost loss allows for more water to access more soil and bedrock, increased weathering most likely explains these significant increases. In fact, the annual pulse of sulfate in the Yukon River jumped by 60 percent over the past thirty years. The new study suggests that groundwater, enriched with organic carbon and other minerals, is likely contributing to these changes.
Another recent study documented similar changes on another major Arctic river, the Mackenzie River in Canada. With two of these rivers showing striking, long-term changes in their water chemistry, these trends strongly suggest that permafrost loss is leading to massive changes in hydrology within Arctic and boreal forest that may have consequences for the carbon cycle, fish and wildlife habitat and other ecosystem services, according to Toohey.
How long the river stays frozen plays an important role in erosion. The Yukon River ice has been breaking up earlier and earlier, often accompanied by tremendous flooding events that devastate the communities on its banks. At the same time, the river has been freezing up later and later. When the river is unfrozen, its banks and soils are more susceptible to erosion. Phosphorous, often a product of this erosion, has increased by over 200 percent during December.
All of these increases impact the aquatic ecosystems of the Yukon River and may ultimately contribute to changes in the Arctic Ocean. Together, said the authors, the research shows that permafrost degradation is already fundamentally transforming the way that high-latitude, Northern Hemisphere ecosystems function.
—Catherine Puckett is Deputy Public Affairs Officer at the USGS Office of Communications. This post originally appeared as a news story on the USGS website.