Old Carbon in Arctic Fish: What Thawing Permafrost Means for Food Webs

As the Arctic warms, thawing permafrost releases "old carbon" — carbon locked in frozen ground for hundreds or even thousands of years. That carbon can supply a lot of energy to food webs, but it has been unclear whether it actually reaches the food that aquatic animals eat, and whether it is becoming more available or important over time.

Researchers from the National Park Service, the U.S. Geological Survey and universities used fish as natural samplers of Arctic waters to find out.

Ten fish species were collected and tested for radiocarbon. Because fish had been collected at the same places about 40 years earlier, the new samples could be compared for changes linked to climate, such as carbon released by thawing permafrost. USGS/Vanessa von Biela.

What they found

• Freshwater food webs used the oldest carbon: on average, fish there were built from carbon more than 1,000 years old.
• Marine food webs used the youngest: carbon averaging about 300 years old.

Then and now

Their study area was one of the first places in the world where the age of the carbon in fish had been measured, about 40 years ago, which let the team see how things had changed. Despite evidence that permafrost thaw is unlocking old carbon, the fish were actually using less old carbon than before — suggesting old carbon may be less important to these food webs than it was in the past.

The results help explain how carbon cycling, including permafrost thaw, affects the animals that live in Arctic waters.

Sources

• National Park Service: "The role of old carbon in aquatic food webs," summarizing research by the National Park Service, the U.S. Geological Survey and university partners; see also USGS Alaska Science Center, "Nearshore Fish Surveys in the Beaufort Sea."