At the turn of the season as snow and ice melt, Alaska’s waterways open up. “This is the highest this river will be this season,” Jason Dobkowski said. “Here is this giant flush of particulate and nutrients that flow through the river. So we are trying to make sure we sample at this big flush period at the beginning of the season.” Water he collects from the Sagavanirktok River on the North slope of Alaska teaches us more about how carbon and carbon dioxide cycle through Earth’s systems.
The sights can be astounding. “While it was melting and we were out collecting a sample we’d see a giant boulder, almost the size of a car, tumbling down this river. It is quite dramatic and surprising to see how much ice and how much material this river transports— so quickly too,” Dobkowski said. “The Sag [Sagavanirktok] flows from the Brooks Range mountains all the way up to the Arctic Ocean,” and “All of this water will eventually end up in the Arctic Ocean.” Understanding conditions along every step of that journey will help clarify climate models, simulations of future climate conditions.
Dobkowski studies Arctic ecosystem ecology at the University of Michigan in the Department of Ecology and Evolutionary Biology and serves as a lab manager for Dr. Geoge W. Kling. Dobkowski has ranged Alaska’s North Slope along with Collin Ward, University of Michigan PhD Candidate in the Earth and Environmental Sciences who assists his adviser Dr. Rose Cory in Arctic research.
“We sample the lower stretches of the river near Toolik Lake all the way to the Arctic Ocean. There are 5 sampling sites and we take samples at each site while another group of people on our team sample the headwaters,” Ward explained. The expeditions provide the team with “A snapshot of the water as it is traveling through the river system or through the river continuum in one day. We can characterize the different types of carbon, or how the carbon is processed, as it is flowing downstream and is exported to the Arctic Ocean.”
The water flows brown. Dr. Rose Cory, University of Michigan professor of aquatic geochemistry, studies naturally occurring organic carbon in streams, rivers, and lakes. She described organic carbon as “Naturally occurring carbon that’s made from decaying plant and soil matter and organisms in the watershed. It’s what gives the water its brown to yellow color.”
Much of the Arctic is underlain with soil that remains frozen year-round, called permafrost. For thousands and thousands of years Arctic temperatures have been so cold that dead plants, instead of decaying fully, become part of the ground. When you set foot on Far North tundra, you might be standing on a layer of ground composed of dead plants (and even long-dead animals like steppe bison) up to 650 meters [2,132 feet] thick. Wow! There is carbon in every living thing (and everything that was once alive), so permafrost holds a lot of carbon. The frozen organic matter in permafrost worldwide contains an estimated 1,600 billion tons of carbon, which is more than twice as much as the carbon currently aloft in Earth’s atmosphere.
Summer Arctic sun normally thaws only the top 30 to 100 centimeters [12 to 39 inches] of the ground. It’s called the active layer, and it’s where plant growth and water flow happens. Water moving atop or through the active layer picks up dissolved organic carbon and turns brown, much like the water you use to make tea. The amount of carbon it can accumulate is limited because frozen permafrost below forms an impassable base and keeps its ancient organic carbon locked away.
But now, the Arctic is warming twice as fast as other regions of the world. These extreme warming trends are changing the state of permafrost.
Scientists like Cory, Kling, Dobkowski and Ward are working to understand and predict the fate of the carbon previously locked away (sequestered) in permafrost. What happens if the active layer deepens and exposes ancient organic matter to liquid water? How much carbon re-enters the carbon cycle when the underground ice that once maintained the stability of permafrost melts thermal erosion causes more and more ground to be exposed to sunlight? Thawing permafrost, like that seen at Wolverine Lake, makes once frozen soil slump and slide downhill where possible. It often enters streams and other water; warming temperatures cause more organic carbon to enter Arctic waterways.
“With 24 hours of daylight and warmer temperatures, thaw happens. You see it first as a yellow trickle in the snow and the color yellow is from all that soil organic matter that’s being washed downstream as the ground is thawing,” Cory explained. “That’s all that beautiful organic carbon that I love, and it rushes into lakes and streams.”
Water from snowmelt inundates the active layer. It flows, moving on top of the ground or just below the surface through water tracks, eventually reaching small streams or ponds and flowing into rivers bound for the ocean. During this process water rich with dissolved organic carbon collects, looking darker and darker. Standing on the shore of the Sagavanirktok River Dobkowski described: “Right now it does look kind of chocolate-milk brown and very dark and cloudy but as the season progresses that brown color will disappear and will look actually more teal, light blue teal, still cloudy because of all the mineral sediments coming from up stream in the mountains.”
As the color shows, carbon enters the system and undergoes complex processes that we’ll explore further along with the scientific team in upcoming articles and videos.
Dobkowski said: “So as that carbon gets released, it’s now being exposed to biological and chemical processes that it has been kept away from for thousands of years when it was frozen and what we want to know is how this carbon that has been cold and dark is going to react.”
Laura Nielsen 2015
Frontier Scientists: presenting scientific discovery in the Arctic and beyond
- ‘Sunlight controls water column processing of carbon in arctic fresh waters’ Cory, R.M., C.P. Ward, B.C Crump, G. W. Kling (2014) Science, 10.1126/science.1253119