A new study by a University of Copenhagen researcher has found that thawing permafrost in Alaska is causing colder water in smaller rivers and streams. This surprising consequence of climate change could affect the survival of fish species in offshore Arctic waters.
Researchers in the study discovered that thawing permafrost causes groundwater to flow deeper, where it becomes cooler than near the ground surface.
Rising global temperatures are causing frozen Arctic ground – permafrost – to thaw. In a new study, researchers have discovered something surprising: small rivers, streams and creeks that flow into larger lakes and coastal waters appear to get colder as permafrost melts. The phenomenon has previously been documented in Russian rivers in the Arctic. But until now, no one had investigated why the water was getting colder even though the air temperature was warming and the permafrost was thawing.
Together with researchers from the U.S. Geological Survey Alaska Science Center, Associate Professor Ylva Sjöberg of UCPH’s Department of Geosciences and Natural Resources Management has shed new light on this cold water. Researchers in the study discovered that thawing permafrost causes groundwater to flow deeper, where it becomes cooler than near the ground surface.
“Permafrost is just below the surface of the ground. When the permafrost is intact, groundwater from springs and mountains flows onto the permafrost layer, where it is strongly heated throughout the summer. However, when the permafrost disappears, the runoff seeps deeper into the ground and it cools before entering nearby streams, rivers and lakes, ” explains Ylva Sjöberg, lead author of the study.
Another complication of climate change
In their study, the researchers examined the Noatak National Preserve in northwest Alaska. Like other Arctic areas, the Noatak has higher temperatures due to climate change.
However, there is very little data available on how climate change is affecting the temperature of smaller water streams. The researchers positioned 62 measurement sensors in different streams in areas with and without permafrost. Here they observed that water temperatures were warmer in areas covered with permafrost.
Using a computer model, the researchers were able to calculate that summer water temperatures in permafrost areas would average 11 degrees, while in areas without permafrost they would average 4 degrees.
“We have no reason to believe that our observations would be different in Alaska or in other Arctic regions with analogous landscapes. This complicates the effects of climate change, as it appears that areas with permafrost are not subject to the same simple ratio of temperature increases in air and water as used elsewhere “, explains Professor Ylva Sjöberg.
Could affect fish stocks
Salmon, grayling and sculpin are some of the fish species that spawn and grow in these streams. Fish biologists at the U.S. Geological Survey’s (USGS) Alaska Science Center made preliminary observations about how cooler water temperatures might affect fish.
“Stream temperature ultimately determines a fish’s ability to reproduce and survive. We suspect that colder water can limit a fish’s growth and probably its ability to thrive,” explains Michael P. Carey, USGS fish biologist.
According to biologists now analyzing the study data, permafrost thaw may also bring other factors that can disrupt the aquatic environment of these fish.
“Streams draining from areas of thawing permafrost are likely to show not only temperature fluctuations, but also increases in carbon and nutrient runoff,” Carey concludes.
Heiner Kubny, PolarJournal