Collaborative Research: Fresh water and heat fluxes to the Arctic Ocean modeled with tree-ring proxies

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Arctic Ocean sea ice has been declining for several decades. As the ice retreats, more open water is exposed, which reduces the amount of light reflected back from the Arctic and leads to further Arctic warming and sea ice loss. This feedback contributes to the amplification of warming across Arctic regions, which is changing the regular connections between river water and atmospheric circulation, and consequently the heat and energy flowing into the Arctic Ocean. Modern observations of Arctic river flow, and estimates of associated heat budgets, rarely extend back more than several decades. These records are too short to fully quantify the long-term trends in freshwater flow and heat budgets, which makes it difficult to understand the processes underlying those trends. This research helps fill that gap by utilizing tree-ring records and river gauge data in the Arctic to reconstruct and study multi-century fluctuations of water, heat and energy flow to the Arctic Ocean.This research uses a wide array of existing and newly collected tree-ring data, coupled with a long record of river gauge data, to develop and test reconstructions of water flow and heat budgets for the Yenisei River, the second largest river of the Arctic. Causal attribution of spatial-temporal variations of river hydrology requires consideration of changing snowmelt, thawing permafrost, and modification of natural flow regimes by dams and reservoirs. This consideration is assessed with the New Hampshire University Water Balance Model. With the engagement of multiple layers of instrumental and modeled data updated to 2020 (e.g., climatic, hydrologic, anthropogenic, General Circulation Model (GCM) outputs) the team is using over 300 tree-ring records from Siberia to reconstruct river discharge and water temperature for the last 300 years. In addition to conventional tree-ring width measurements, the heat transport reconstruction explores the signal for river temperature variation in the wood anatomy of tree rings. Overall, this effort is identifying climatic drivers of past river energy flux variations in the Arctic. The researchers place runoff features of the gauged period, as well as the annual, multi-decadal, and centennial variability from the reconstructed periods, in the context of GCM projected runoff changes for the next century. While the Yenisei River is the direct focus of the research, a broad goal is an extension of the approach, methods, and tools to other pan-Arctic regions. To assist other researchers, the team is developing a new online toolbox (TR-RIMS, Tree-Ring Regional Integrated hydroclimatic Modeling and analysis System). The tool synthesizes tree-ring signals for the heat and volume of Yenisei River and adopts a non-parametric statistics for the spatial reconstruction. The online TR-RIMS tool enhances the infrastructure for both research and education and enable societal understanding of natural hazards and environmental change induced by the Arctic amplification. The research also promotes international scientific collaboration in the Arctic to boost international and interdisciplinary collaboration exploring biogeochemical, geophysical and ecological processes underlying Arctic system change.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.