Grantee Research Project Results
Tracking Arctic Climate Change With Calcium IsotopesEPA Grant Number: FP917193
Title: Tracking Arctic Climate Change With Calcium Isotopes
Investigators: Lehn, Gregory Owen
Institution: Northwestern University
EPA Project Officer: Just, Theodore J.
Project Period: August 25, 2010 through August 24, 2013
Project Amount: $111,000
RFA: STAR Graduate Fellowships (2010)
Research Category: Academic Fellowships , Fellowship - Global Change
Permafrost contains vast quantities of frozen organic carbon that will likely transform to greenhouse gasses (e.g., CO2 and CH4) upon thawing, which will contribute to global climate change over the next 100 years. Rivers and permafrost appear to have distinct calcium (Ca) isotope compositions due to seasonal differences in chemical weathering and hydrologic processes. This research will employ calcium isotope composition (d44Ca) of Arctic Alaskan river changes as a function of permafrost thaw depth due to seasonal differences in chemical weathering and hydrologic processes, which can be used to understand, monitor, and predict the rate and extent of permafrost thawing.
Permafrost contains vast quantities of frozen organic carbon that will likely transform into greenhouse gases upon thawing. Current and future Arctic warming could create a positive feedback to global warming, as a warmer climate will release more carbon, which in turn will favor more warming. This research proposes to use calcium isotopes to understand, monitor, and predict the rate and extent of permafrost thawing and associated organic carbon release.Approach:
I will concentrate on six rivers draining the North Slope of Alaska near the Toolik Lake Long-Term Ecological Research Station. By comparing data between rivers draining bedrock versus those that drain both bedrock and permafrost, I will isolate soil zone processes. I will collect water samples from early spring through late fall following established protocols and collect soil cores from each watershed. In the laboratory, I will measure cation and anion concentrations, Ca isotope concentrations, and dissolved organic carbon (DOC) concentrations. Data synthesis will include major ion mass-balances, carbonate equilibria calculations, isotope mixing equations, hydrograph separations, and reactive transport modeling to determine permafrost thaw mechanisms.Expected Results:
Rivers and permafrost appear to have distinct Ca isotope compositions due to seasonal differences in chemical weathering and hydrologic processes. When permafrost melts during the summer, the isotope composition of rivers approaches that of permafrost. In the late fall (mid-September in the Alaskan Arctic), the melt depth reaches its maximum extent before the freezing front moves downward from the surface at the onset of winter. In a warmer world, the extent and duration of melting will likely increase, which implies that the “isotopic fingerprint” of permafrost in rivers will be more evident for a longer period of time. Combined with concentration of DOC, the Ca isotope composition of rivers can track the quantity of carbon reintroduced into the carbon cycle as the active layer deepens.
Potential to Further Environmental/Human Health Protection:
With the dependence of humanity on the environment, climate change threatens human health and economies through alteration of water and food sources, ecosystems, agriculture, and weather patterns. Since the permafrost could contribute a significant amount of carbon to the global cycle, a better understanding is necessary to predict its effects on global climate change. This information is crucial to current and future policy makers in their attempt to mitigate the effects of climate change.Supplemental Keywords:
Arctic, climate change, calcium isotopes, permafrost, thaw, Alaska, river geochemistry, tundra,