ABSTRACT

This award funds a new method for measuring black carbon in lake-sediment cores, which builds on a well-established technique for measuring black carbon in glacial ice cores. Black carbon (BC) is a primary climate forcing agent resulting from incomplete combustion of biomass. Wildfire emissions are critical unknowns in climate-model predictions under a warming climate, particularly the relationship of large-scale biomass burning and BC emissions to climate forcing. Development of the ice-core BC method has transformed understanding of BC in polar regions; this project will further develop the sediment-core BC method and apply it to provide additional records that will expand temporal and spatial coverage to other regions, including development of detailed lake-sediment records of Arctic BC during the past ~1.4 million years thereby extending understanding of climate and biomass-burning linkages. This will enable worldwide, longer-term understanding of linkages between climate, human activities, and biomass burning, as well as quantification of BC as a forcing agent. BC aggregates reflect regional-to-hemispheric biomass burning emissions rather than local biomass burning. Given the sparsity of ice-coring locations in the eastern Arctic, application of this new lake sediment method in Arctic Russia will enable widely distributed records of past biomass burning and BC forcing in the region, potentially transforming understanding of forcing scenarios through time. Analysis of samples from Lake El'gygytgyn will extend biomass burning records much farther back in time than is possible with ice cores or charcoal records. The development and interdisciplinary interpretation of such long-term BC records will greatly extend instrumental records of biomass burning and BC in space and time - through a broad range of climate states and forcing scenarios - in line with the goals of NSF's Paleo Perspectives on Climate Change (P2C2) program.

This project will exploit the availability of archived lake sediment samples from the eastern Arctic and use this new method to (1) develop ~2,000-year-long records of BC, which is related to biomass burning in the eastern Arctic, to determine linkages between climate, human activities, BC, and biomass burning in the region; (2) evaluate the validity of the lake sediment method of measuring BC for different climate states by comparing BC flux and particle mass in the upper ~150,000 years of the Lake El'gygytgyn sediment core with a reprocessed ~120,000-year BC record from the Greenland NEEM ice core; and, (3) quantify and understand linkages between long-term and large-magnitude climate change, BC, and biomass burning in the eastern Arctic by developing a detailed sediment BC record from Lake El'gygytgyn during the past ~1.4 million years (spanning Marine Isotope Stage (MIS) 1 to MIS 45). To meet the goals of this project, BC concentration and particle mass measurements will be made in lake sediment samples from an array of shorter, higher-time-resolution cores from the Russian Arctic, as well as from deeper, lower-time resolution lake cores, including the upper ~60 m of the Lake El'gygytgyn core. Pilot BC measurements from Lake E sediment cores for the past 160,000 years show close correspondence with large-scale climate (e.g., insolation, greenhouse gas concentrations) but suggest different climate-vegetation-fire relationships during the glacial periods than reported for the Holocene interglacial. This award is co-funded by the Office of Polar Programs and the Division of Earth Sciences.

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.

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