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MS defense: Chloe Brashear

Wednesday, July 21, 2021, 10:00AM - 11:00AM


Chloe Brashear



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High-frequency climate variability in a Greenland ice core during the past 50 thousand years


Stable isotopes of hydrogen and oxygen in polar ice cores provide information about local temperature and atmospheric circulation. We use a multi-taper method (MTM) of spectral analysis on a continuous high-resolution (i.e. mm-scale) Greenland water isotope record, recently recovered from the East Greenland Ice Core Project (EGRIP), to determine how interannual and decadal temperature variability changed throughout the past 50 thousand years. We are specifically interested in trends across the most recent glacial-interglacial transition and across millennial scale Dansgaard-Oeschger (i.e. stadial-interstadial) cycles to elucidate how large temperature changes affect variability around the mean in Greenland. To further understand global relationships in variability, we later make comparisons with mm-scale ice core records from the South Pole (SPC) and the West Antarctic Ice Sheet Divide (WDC). Our results reveal a strong coupling between mean temperature and high-frequency (i.e. 7-15 year) climate variability at EGRIP. On average, the Last Glacial Period (LGP; 11.7-50 ka bp) exhibits 2.5 times greater variability than the Holocene and within the context of the LGP, cold stadial periods are 1.5 times more variable than warm interstadial periods. We provide a plausible mechanism for the trend we observe across Dansgaard-Oeschger (DO) cycles in northeast Greenland: a larger sea ice area coupled with a more variable sea ice front may explain the increased isotopic variability during cold stadial periods. In contrast, neither Antarctic site (SPC or WDC) exhibit changes in high-frequency variability across millennial scale warm phases, known as Antarctic Isotope Maxima (AIM) events, that occur with each DO Event. While elucidating exact forcing mechanisms for observed trends in high-frequency variability is outside the scope of this study, we provide critical benchmarks and reasonable hypotheses to test in future climate modeling research.


Open to the public.