The role of old carbon in aquatic food webs

Ten different species of fish were collected and tested for radiocarbon content. Because fish had been collected about 40 years ago, recent samples could be compared for any changes that could be attributed to climate change impacts, such as carbon released by thawing permafrost.

USGS/Vanessa von Biela

Researchers from the National Park Service, the U.S. Geological Survey, and universities investigated carbon in Arctic fish food webs. As the climate warms, permafrost thaw is releasing "old carbon"—carbon that had been trapped in ice for hundreds or even thousands of years. They found that fish in freshwater food webs used carbon that was more than 1,000 years old on average and fish in marine food webs used carbon that averaged about 300 years old. Because their study system was one of the first parts of the world with measurements of carbon ages in fish from about 40 years ago, there was a chance to understand how climate has shifted the age of carbon in aquatic food webs over time. Despite evidence of permafrost thaw unlocking old carbon, they found that fish actually used less old carbon over time. These data provide insights about the interplay of carbon cycling processes including permafrost thaw influence on animals.

Scientific Significance Statement

As the Arctic warms and permafrost thaws, older carbon (hundreds to many thousands of years old) is released, which can contribute a substantial amount of energy to food webs. Yet, we do not know if older carbon is in the food eaten by aquatic animals or if it is becoming more available or important over time. In this study, we used fish as natural samplers of aquatic ecosystems and found older carbon was used most in freshwater food webs and least in marine food webs. We then compared our results to similar fish data from ~ 40 yr earlier and found that older carbon may be less important than in the past.

Also see: Nearshore Fish Surveys in the Beaufort Sea for more information about this study.

Arctic fishes reveal patterns in radiocarbon age across habitats and with recent climate change

Abstract

Climate change alters the sources and age of carbon in Arctic food webs by fostering the release of older carbon from degrading permafrost. Radiocarbon (¹⁴C) traces carbon sources and age, but data before rapid warming are rare and limit assessments over time. We capitalized on ¹⁴C data collected ~ 40 years ago that used fish as natural samplers by resampling the same species today. Among resampled fish, those using freshwater food webs had the oldest ¹⁴C ages (> 1,000 yr BP), while those using marine food webs had the youngest ¹⁴C ages (near modern). One migratory species encompassed the entire range of ¹⁴C ages because juveniles fed in freshwater streams and adults fed in offshore marine habitats. Over ~ 40 yr, average ¹⁴C ages of freshwater and marine feeding fish shifted closer to atmospheric values, suggesting a potential influence from “greening of the Arctic.”

Stanek, A. E., M. P. Carey, J. A. O'Donnell, S. M. Laske, X. Xu, K. H. Dunton, and V. R. von Biela. 2024. Arctic fishes reveal a gradient in radiocarbon content and use. Limnology and Oceanography Letters.