Shining Light on the Global Carbon Cycle

Colored dissolved organic matter interacts with light uniquely, based on the carbon source and molecules present. Think of coffee or tea - origin, elevation and cultivar can impact optics, flavor and aroma of your favorite cup. All of these properties carry information on the basic building blocks, or organic molecules, in the beans or leaves.

Colored dissolved organic matter is the tea of the sea. By characterizing the material with light, we can better understand origins and fate of this critical component of the global carbon cycle.

And by interacting with light, these molecules impact the color of water. From the Alaskan tundra, to the Yukon River, across the river plume and into the Bering Sea, these changes are visible to our eyes and from satellites.

Landsat 8 Surface Reflectance True Color product (July 2017). Image courtesy of NASA GSFC

The Tea of the Sea - from Space

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Colored molecules uniquely absorb light, allowing presence and estimates of composition from space. By leveraging satellites, we can view carbon dynamics at unprecedented scale. Dissolved organic carbon accounts for nearly 700 Pg of fixed carbon in the global biosphere, nearly equivalent to the amount of carbon in the atmosphere. Understanding reactivity and remineralization of this carbon pool is critical to understand potential positive and negative climate feedbacks.

Colored dissolved organic matter inputs from the Little Elm River into Lake Superior. Depending on the source and concentration of colored molecules, waters can range from a coffee black color ("blackwaters") to a more faint, green tea color. Here, the tannin-rich waters of the Little Elm contrast strongly with the clear Lake Superior waters.

Colored dissolved organic matter absorption in Long Island Sound, estimated over all available scenes in July 2018 from the European Space Agency's Sentinel-3 Ocean and Land Colour Instrument.

Experience in the Field

My research has spanned wetlands, rivers, lakes and the oceans. I've worked in highly perturbed urban estuaries and EPA listed Areas of Concern, as well as more pristine Arctic waters. All of this work has been possible thanks to the hard working Captains and crew of the:

R/V Neeskay in Lake Michigan
R/V Blue Heron and R/V Agassiz in Lake Superior
R/V John Dempsey in Long Island Sound
F/V Anchor Point in the Bering Sea
R/V Aliuq in the Elson Lagoon and Beaufort Sea

Of course, sampling can be challenging. To access field sites, I have also relied on coastal Alaskan communities in the Yukon delta, kayaks in coastal marshes and charter fisherman in Long Island Sound.