Himalayan glaciers are melting due to atmospheric warming, with the potential to limit access to water for more than 25% of the global population that resides in these glacier meltwater catchments. Black carbon has been implicated as a factor that is contributing to Himalayan glacier melt, but its sources and mechanisms of delivery to the Himalayas remain controversial. Here, we provide a 211- year ice core record spanning 1781-1992 CE for refractory black carbon (rBC) deposition from the Dasuopu glacier ice core that has to date provided the highest-elevation ice core record (7200 m). We report an average rBC concentration of 1.5 μgL-1(SD = 5.0, n = 1628) over the 211-year period. An increase in the frequency and magnitude of rBC deposition occurs after 1877 CE, accompanied by decreased snow accumulation associated with a shift in the North Atlantic Oscillation Index to a positive phase. Typically, rBC is deposited onto Dasuopu glacier during the non-monsoon season, and short-lived increases in rBC concentration are associated with periods of drought within neighboring regions in northwestern India, Afghanistan, and Pakistan. Using a combination of spectral and back-trajectory analyses, as well as a comparison with a concurrent analysis of trace metals at equivalent depths in the same ice core, we show that biomass burning resulting from dry conditions is a source of rBC to the central Himalaya and is responsible for deposition that is up to 60 times higher than the average rBC concentration over the time period analyzed.We suggest that biomass burning is a significant source of rBC to the central Himalaya and that the rBC record can be used to identify periods of drought in nearby regions that are upwind of Dasuopu glacier.
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Acknowledgements. This work was funded by the NSF Atmospheric Chemistry Program, the NSF-ESH program, The Ohio State University, the Ohio State Committee of Science and Technology, and the National Natural Science Foundation of China. We thank the many scientists, engineers, technicians, and graduate students from the Byrd Polar and Climate Research Center and the Lanzhou Institute of Glaciology and Geocryology (China) that contributed to the collection and previous analysis of the Dasuopu ice core. We are grateful to Julien Nicolas for performing the graphic display of the back trajectories. We thank two anonymous reviewers who provided input to greatly improve this paper.
Financial support. This research has been supported by the NSF
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