Arctic melt and summer temperature during past warm periods: a new ice core proxy

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Glacier ice melt in the Arctic has profound impacts on local communities, ecosystems and infrastructure, and global sea level. Long-term records of past ice melt help scientists better understand the processes that contribute to ice melt, such as summer air temperatures and the concentration of soot and other particles in the ice that absorb sunlight. In particular, past warm periods are important to study because they provide potential analogs for our future climate. One method to reconstruct past surface melt is through visual detection of bubble-free layers. However, beyond approximately 5000 years, the melt layers are no longer visible because the ice layers get strongly thinned by ice flow and because the air bubbles dissolve into the ice crystals. This award supports the development of a new technique to reconstruct past melt in Arctic ice cores and the application of this technique to study past warm periods in Arctic ice cores from Greenland and Alaska. The award supports a graduate student at Oregon State University, contributing to the STEM (Science, Technology, Engineering and Mathematics) workforce. The researchers will develop lesson materials on ice cores and climate change for middle and high school students from underserved regions, host two STEM teacher workshops at OSU, and to support student clubs across Oregon rural communities.Glacier ice cores preserve a record of past surface melting that can be used for understanding past variability in melt intensity in response to climate forcing - either natural or anthropogenic. Researchers have traditionally reconstructed past surface melt in ice cores using visual detection of bubble-free layers. Unfortunately, this method does not work for old and/or deep ice, where melt layers can no longer be visually identified. The investigator will apply a new ice core proxy for surface melt intensity: the xenon/nitrogen ratio. In the absence of refrozen meltwater, the xenon/nitrogen ratio in ice samples reflects the atmospheric ratio. However, because of the high solubility of xenon, the xenon/nitrogen ratio becomes strongly enriched in the presence of surface melt. The investigator will use this proxy to address four important scientific questions: (1) what is the timing and magnitude of the Holocene Thermal Maximum in the Arctic; (2) what is the extent and magnitude of Greenland melt during the Last Interglacial period; (3) what are the drivers of Arctic melt on long time scales; and (4) how do current melt rates in the Arctic compare to the last 10,000 years. The investigator proposes measurements on the Renland and GISP2 ice cores (both from Greenland), and the Mt. Hunter ice core (from Alaska). The xenon/nitrogen melt proxy will be calibrated to reconstruct local summer temperature. The proposed work uses existing ice core samples and does not involve Arctic fieldwork. The award supports a graduate student at Oregon State University, contributing to the STEM (Science, Technology, Engineering and Mathematics) workforce. The researchers will develop lesson materials on ice cores and climate change for middle and high school students from underserved regions, host two STEM teacher workshops at OSU, and to support student clubs across Oregon rural communities.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.