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News & Events

PhD defense - Abby Hughes

Friday, April 02, 2021, 10:30AM - 12:30PM

Speaker

Abby Hughes

Title

​Ice core water isotope records: Analysis of high-resolution Greenland ice cores and experimental determination of post-depositional effects on surface snow

Abstract

Polar ice cores contain multiple proxies which record vast amounts of climate information over hundreds of thousands of years. Water isotopes in ice cores can be used to infer past temperature and atmospheric circulation patterns, and with recent advances in technology can be measured at very high resolution. Here, I present analyses of continuous water isotope records from two new Greenland ice cores, and use snow surface experiments to work towards improving our interpretation of ice core records.

The Renland Ice Cap is located in East-Central Greenland, and an ice core drilled in 2015 contains a seasonally-resolved water isotope signal through 2.6 ka and sub-decadal signals through 8 ka. Using spectral analysis, I find that decadal (i.e., 15-20 year) isotope variability at Renland co-varies with North Atlantic sediment core indicators of ocean circulation patterns throughout the Holocene. Furthermore, analysis of the seasonal signal reveals that a decreasing trend in the winter isotope signal may correspond to an increase in Arctic sea ice cover and a decrease in total annual insolation over the last 2.6 ka. Together, these findings show that coastal Greenland climate may be closely tied to regional sea surface conditions.

The East Greenland Ice Core Project (EastGRIP) is an ongoing drilling campaign in Northeast Greenland, with a record currently extending to 50 ka. EastGRIP has sub-decadal isotope signals preserved through the Glacial period, and for the first time we have a continuous Glacial record for multiple isotope parameters (i.e. δ18O and deuterium excess). Through comparison to a North-Central Greenland ice core record, I demonstrate the importance of high-resolution sampling and expand on our understanding of spatial variability in Greenland climate. Additionally, an analysis of abrupt climate events throughout the Glacial period indicates that rapid warming is preceded by a shift in North Atlantic atmospheric circulation patterns; this has important implications for our understanding of mechanisms occurring during abrupt climate changes.

Many aspects of the isotope-climate relationships are well constrained through decades of research; however, there remain gaps in our understanding of processes taking place at the surface of the ice sheet between depositional precipitation events, and how they influence the recorded climate signal. To address this I use a series of laboratory experiments to show that in a controlled environment the snow isotopic composition changes rapidly due to sublimation, with this finding supported by model results. Complementary field experiments demonstrate that in a natural setting, the top 4 cm of the snow surface evolves on an hourly timescale due to sublimation and exchange with atmospheric vapor. These results suggest that water isotopes may effectively integrate across multiple parameters to record a more continuous climate signal, which may improve isotope-enabled climate models and inform our interpretation of ice core water isotope records.