Land Cover and hydrology - assessing controls on Si cycling in a changing Arctic

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Dr. Joanna C. Carey has been awarded an NSF EAR Postdoctoral fellowship to carry out a research and education plan at the Marine Biological Laboratory in Woods Hole, MA. Her research will examine how shifting land cover and permafrost thaw is altering silicon (Si) biogeochemistry in the Arctic. By examining ten large river systems in Alaska, this project will quantify how warming of the terrestrial landscape is altering Si availability in downstream receiving waters. Because Si availability in marine systems is critical for the survival of diatoms, the most abundant type of phytoplankton in marine waters, the results of this research will have direct implications for marine carbon dynamics. Land cover and hydrology are two important controls over Si export to marine systems, but to date these factors have yet to be examined in conjunction in Arctic ecosystems. In addition to a lack of baseline information on Arctic Si cycling, the rapid pace of warming in polar latitudes makes this work timely. The education arm of this fellowship will consist of engagement with local Alaskan communities through working with the Yukon River Inter-tribal Watershed Council and outreach with public high school Earth Science courses in Providence, RI to teach students about climate change and Arctic ecosystems. In addition, Dr. Carey will share the results of her research results with policy makers. Although geochemical factors exert large controls over riverine Si fluxes, watershed land cover (i.e. terrestrial vegetation) has also recently been identified as another important control over riverine Si fluxes in temperate and tropical systems. However, the role of terrestrial biological processes has yet to be examined in the Arctic. Hydrologic flowpaths, including water residence time, is another critical driver of riverine Si fluxes. Both of these factors are rapidly changing in Arctic ecosystems due to recent warming, potentially impacting the magnitudes and timing of Si exports to coastal receiving waters and shifting phytoplankton species compositions. The novel use of germanium (Ge)/Si tracers will allow Dr. Carey to decipher between geochemical vs. biological drivers of Si fluxes across a gradient of vegetation and permafrost cover. Using a space-for-time substitution, this work will create the first predictive framework of how future warming will alter Si availability in marine waters.