Carbon cycling through the environment is an essential part of life on this planet.
Understanding the different sources and reservoirs of carbon is a major focus of Earth science research. Plants and animals use the component of cellular growth. It can be stored in rocks, minerals or in the ocean. Carbon in the form of carbon dioxide can move into the atmosphere, where it contributes to a warming planet.
A new study led by researchers from Florida State University finds that plants and small organisms in Arctic rivers could be responsible for more than half of the organic particles flowing into the Arctic Ocean. This is a much larger percentage than previously estimated, and has implications for how much carbon is sequestered in the ocean and how much it moves into the atmosphere.
Scientists have long measured organic matter in rivers to understand how carbon circulates through watersheds. But this research published in Proceedings of the National Academy of Sciencesshows that organisms in major Arctic rivers are a major contributor to carbon export, accounting for about 40 to 60 percent of the organic particulate matter — small parts of decomposing organisms — that flows into the ocean.
said Rob Spencer, professor in the Department of Earth, Oceanography and Atmospheric Sciences. “This study highlights that there is a lot of life in these same rivers and that a lot of the organic matter that is exported comes from production in the rivers.”
Scientists study carbon exported through waterways to better understand how the element circulates through the environment. When organic matter decomposes on land, it can move into rivers, which in turn drain into the ocean. Some of that carbon supports marine life, and some of it sinks to the ocean floor, where it gets buried in sediment.
The researchers looked at the six major rivers that flow into the Arctic Ocean: the Yukon and Mackenzie in North America, and the Ob, Yenisei, Lena and Kolyma rivers in Russia. Using data collected over nearly a decade, they built models that use stable and radioisotope carbon signatures and carbon-to-nitrogen ratios of particulate organic matter to determine the potential sources’ contribution to the chemistry of each river.
Not all organic particles are formed equal with carbon from soil washed downstream being more likely to be buried in the ocean than carbon produced within a river. The carbon is likely to remain floating in the ocean, to be fed by organisms there, and eventually to be breathed out in the form of carbon dioxide.
“It’s like the difference between a fried potato and a stalk of broccoli,” said Megan Behnke, a former University of Alaska Southeastern doctoral student. “This broccoli will keep in stock in your freezer, but the French fries are more likely to be eaten.”
This means that a small increase in the river’s biomass can equate to a larger increase in organic matter coming from the land. If the carbon in that organic matter were to pass into the atmosphere, it would affect the rate of the carbon cycle and associated climate change in the Arctic.
“I always get excited as a scientist or researcher when we find new things, and this study found something new in the way these big Arctic rivers work and how they export carbon to the ocean,” said Spencer. “We have to understand the modern carbon cycle if we’re really going to start to understand and predict how it’s changing. This is really important for the Arctic at the rate it’s warming and because of the massive carbon stocks it carries.”
The study was an international endeavor involving researchers from ten different institutions.
“A pan-Arctic scientific view is more important than ever,” Behnke said. “The changes that are happening are much greater than one institution in one country, and we need these long-term collaborations. It is very important to continue.”
Study co-authors include Susan E. Tank from the University of Alberta. James W. McClelland, University of Texas; Robert M. Holmes and Anya Suslova, Woodwell Center for Climate Research; Nigar Hajipur and Timothy E. Eglinton, ETH Zurich; Peter A. Raymond, Yale University; Alexander F. Zolidov and Tatyana Gortovaya, South Russia Center for the Preparation and Implementation of International Projects; Nikita Zimov and Sergei Zimov, Russian Academy of Sciences; Ida A. Mutter, Yukon River Tribal Watershed Council; and Edwin Amos, Western Arctic Research Center.
This research was supported by the National Science Foundation through grants to the Great Arctic Rivers Observatory.