The following is a blog post from a guest writer, Annabeth McCall. She is a PhD candidate based in Germany at the Alfred Wegener Institute, where she studies ocean-color remote sensing in Arctic coastal waters. She is currently on a field expedition to the Canadian Arctic for five weeks to collect data for her dissertation, and was kind enough to write about her research and field experiences for oceanbites!
Heating up in the Arctic
Intensification of climate change in the Arctic is causing increased river flows and permafrost thaw. As a result, erosion and the release of large amounts of carbon-rich material into rivers that feed into the Arctic Ocean is increasing at an alarming rate. Nestled at the interface between the terrestrial and ocean domains, Arctic deltas act as filters and modifiers for carbon, nutrients, and sediments, as well as house important ecosystems that support local communities (1). Rapid changes associated with warming temperatures however may alter the ability for these coastal systems to regulate the increased input of organic carbon. This may lead to a system-wide movement and transformation of organic carbon, shifting Arctic coastal systems from carbon absorbers, or sinks of atmospheric carbon, to releasers, or sources of atmospheric carbon.
Satellites lending a helping hand
Due to their inaccessibility, the fate of carbon across remote Arctic river-ocean systems is not well understood, especially in the face of climate change. Poor data coverage presents a major knowledge gap needed to be filled in order to achieve a true source-to-sink assessment of carbon export and impacts on the global carbon budget.
Fortunately, new advances in satellite technology allow scientists to observe Arctic coastal waters remotely. Special satellite imagery can provide data on water quality at relatively high spatial and temporal resolutions. This imagery, ultimately, provides us with information on water constituents based on its color, and valuable information that can be used to monitor and answer scientific questions.
The color of water, you say?
Have you ever wondered why oceans appear blue, coastal estuaries appear dark brown or green, or why the Colorado River slicing through the Grand Canyon looks similar to a milky iced-latte? It is, in part, due to the particles and substances dissolved in those waters, such as sediments and dark organic materials, but also attributed to how these materials in the water absorb, scatter, and reflect sunlight beaming down. For example, the deep blue ocean absorbs photons of light in the red and green wavelengths of the electromagnetic spectrum, while photons in the blue part of the spectrum are reflected back, thus appearing blue to the human eye. As the ocean mixes with rivers near coastlines, and the materials and organisms in the water blend and change, the photons absorbed and scattered also shift, altering the color and shades we see as humans.
This interaction of sunlight with particles and dissolved substances within the water influences its color, and scientists have found a way to harness this information to determine what is carried by rivers entering oceans. “Ocean-color” satellites can use the power of sunlight transmitted to Earth and absorbed by water, receiving the signal of light reflected back from the water surface, and translating this into usable data (2). This is done at specific channels, or bands, that capture the full wavelengths of the electromagnetic spectrum. This allows us to use the color of water to estimate the amount and type of particles and organic carbon concentrations carried by water, among other things.
Given that river-to-sea systems are so dynamic and complex though, proper in-situ, or “in the field”, water sampling and measurements are necessary to validate these satellite monitoring approaches for future and broader use.
Our field mission
Our research team just landed in the Mackenzie River Delta in the Inuvialuit Settlement Regions of Tuktoyaktuk and Inuvik in the Canadian Arctic. Our mission is to capture the full story of how organic carbon flows from the river, through the delta, and into the coastal waters and out to sea. For 5 weeks, we will traverse the maze of deltaic channels and nearby bays, from freshwater to saline, collecting water samples and deploying a suite of radiometry tools, or light sensors, which measure how sunlight passes through or reflects off of the water. The light sensors will provide us with a color signal, or reflectance, based on the type and concentration of substances which interact with light in the water. These substances include chlorophyll, color dissolved organic matter, and sediment particles.
Water samples collected from our small boats traversing the deltaic channels will be filtered and analyzed in a lab and the results compared with an orbiting satellite collecting images of the Mackenzie River Delta during our 5-week survey. The radiometric, or light, data provides the important link between a traditional water sample analysis and the signals that the satellite perceives based on the reflected light from the color of the water. Scientists can retrieve this information for a particular time and space and monitor coastal changes remotely.
Field work will be led by German-based researchers and facilitated by Inuvialuit community-based partners. Integration of traditional environmental knowledge into this project is critical to both its uniqueness and success, and is an important component to better understand how physical and biogeochemical processes in the shallow water zones are affecting Inuvialuit communities and what that means for their future.
Stay tuned!
Hopefully, our team is able to digest the numbers provided by the “water color”, and paint a scientific picture of coastal processes from this satellite approach. This will resolve our understanding of climate induced land-ocean matter fluxes, permafrost thaw, and associated impacts on one of the most rapidly changing ecosystems on Earth, the Arctic coastal environment.
References
1 Overeem, I., Nienhuis, J.H. & Piliouras, A. Ice-dominated Arctic deltas. Nat Rev Earth Environ 3, 225–240 (2022). https://doi.org/10.1038/s43017-022-00268-x
2 Davies, E.J., Basedow, S.L. & McKee, D. The hidden influence of large particles on ocean colour. Sci Rep 11, 3999 (2021). https://doi.org/10.1038/s41598-021-83610-5
3 Juhls, B, Land-Ocean Interactions in Arctic Coastal Waters: Ocean Colour Remote Sensing and Current Carbon Fluxes to the Arctic Ocean, pg. 27 (2020) Refubium – Land-Ocean Interactions in Arctic Coastal Waters: Ocean Colour Remote Sensing and Current Carbon Fluxes to the Arctic Ocean (fu-berlin.de)
I received my PhD in Biology from Wake Forest University, and I received a BS in Biology from Cornell University. My research focuses on the terrestrial locomotion of fishes. I am particularly interested in how different fishes move differently on land, and how one fish may move differently in different environments. While I tend to study small amphibious fishes, I’ve had a lifelong fascination with all ocean animals, and sharks in particular. When not doing science, I enjoy running, attempting to bake and cook, and reading.
