Collaborative Research: Reconciling conflicting Arctic temperature and fire reconstructions using multi-proxy records from lake sediments north of the Brooks Range, Alaska

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Temperature reconstructions from the region north of the Brooks Range in Alaska suggest a warmer-than-present Last Glacial Maximum (LGM, 26,500 to 19,000 years ago). Global climate models differ strongly in their simulations of this region, with some suggesting a warmer and others a colder cliamte. There are virtually no high-resolution temperature records from this region. Robust temperature reconstructions spanning the LGM to present are therefore needed to test the outputs from climate models and to understand regional sensitivity to climate forcing. Associated with the ambiguous temperature history is uncertainty in the regional fire history, as revealed by the unexpected discovery of three major Alaskan tundra fires in last 150 years. These fires contradict the conventional notion that tundra ecosystems rarely, if ever, burn and stimulate a key question: What are the relationships between climate change, fire, and vegetation since the LGM? This project will develop careful reconstructions of temperatures in the region using records obtained from lake cores. The resulting data will then be compared with a variety of climate model outputs.The project will contribute to workforce development by supporting the training of two graduate students. The students and their mentors will leverage activities of the Brown STEM Outreach Office to K-12 classrooms in Providence, RI, where the classroom population is composed largely of under-represented minorities in the STEM fields. The project will entrain a K-12 teacher into the laboratory during the summer and support the teacher's participation in a major regional science meeting. The team will participate in the Kaktovik Oceanography Program, a project in the Inupiat village of Kaktovik, Alaska for K-12 students. The data collected will be made public and serve as a reference for Alaskan tundra science. Finally, the principal investigators will expand an existing project blog into a dedicated website for public outreach concerning the project.The PIs will generate high resolution, multiproxy records of temperature and fire since the LGM from sediment cores of four lakes on the North Slope of Alaska using a suite of organic geochemical and traditional paleoecological proxies. These data will be tested against predictions from fully coupled climate models to evaluate the ability of IPCC-grade models to simulate past temperature changes, and to evaluate potential forcings and feedbacks that regulate regional temperatures. The work is built upon initial studies that indicate that: 1) strong, quantifiable relationships exist between alkenone distributions and early summer temperature in these lakes, and plant leaf wax D/H ratios in Arctic lake sediments record mean summer temperatures; 2) polycyclic aromatic hydrocarbons (PAH) in lake sediments record the regional fire history; and 3) multiproxy analysis can determine temperature changes in early, middle and mean summer temperatures and will permit critical examination on the impacts of seasonal temperature change and its associated feedbacks and forcing. The PAH approach complements charcoal records and allows detection of paleo-fires across a broader regional scale. Study sites are located within the Toolik Field Station Arctic Long Term Ecological Research (LTER) site, which only began to provide continuous, strategically important monitoring data since 1975. The study will provide fundamental, high quality temperature and fire data, placing the past 40 years of instrumental monitoring in the grand context of the Holocene and late Pleistocene.