How are water isotopes influencing our understanding of Antarctic climate variability over the past 2000 years?

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• Anaïs Orsi
• Thursday 18 March 2021, 15:00-16:00
• Zoom Seminar.

If you have a question about this talk, please contact Daniel Field.

Under the current global warming trend, the Arctic is warming the fastest, and strangely, many parts of Antarctica are not warming at all. The delayed response of the high latitudes of Southern Hemisphere to the Greenhouse warming is an important observation that is not reproduced by the current generation of global climate models. One of the leading hypotheses to explain this discrepancy is that natural variability is particularly large in the southern high latitudes, masking the anthropogenic forcing, and that this large variability is not well reproduced by models. Quantifying internal variability and understanding its cause is important for our understanding of the potential response of Antarctica to climate change, and to improve projections. Here, we will review our knowledge of Antarctic climate variability from ice cores covering the past 2000 years. This is an interval sufficiently short to have observations from many places in Antarctica, and sufficiently long to investigate variability at decadal and longer timescales. Temperature reconstructions come mainly from water isotopes, but they are not a perfect temperature recorder. The central thread of this talk will be to discuss how our vision of climate variability is distorted by the water-isotopes lens. We will discuss the importance of precipitation bias on the deposited ice water isotope signal, using isotope enabled climate models over the reanalysis period (1979-present), and illustrate the impact of this sampling bias by contrasting the expression of circulation modes (such as the SAM ) on temperature and d18O. In the second part of the talk, we will review evidence from other temperature proxies, especially borehole temperature records and temperature reconstructions from inert gas isotopes (d15N-excess), and discuss how the different records can be reconciled into a coherent view of Antarctic climate evolution over the past 2ka. If time allows, we will briefly discuss model-data comparisons over the last millennium, and review hypothesis about why models (OA-GCM) under-estimate internal variability in the high latitude Southern Hemisphere.

This talk is part of the Department of Earth Sciences Seminars (downtown) series.

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