PAOC Colloquium: David McGee (MIT)

"Connecting ancient lake deposits to past atmospheric changes in the southwestern U.S."

At its core, the study of past precipitation changes seeks to understand two basic questions: by how much have precipitation patterns changed in the past, and why have the changed? I will explore these fundamental questions focusing on the southwestern U.S., a water-stressed region that is projected to get drier in the future. For over a century, ancient lake shorelines in California, Nevada and Utah have been studied as a window into periods of dramatically wetter conditions in the past. I will describe how my group is attempting to understand these past wet periods in two of these lake basins – the Bonneville Basin of northern Utah, and the Searles Basin in Southern California. Combining recent findings by our group with other data, I will present a summary of what paleoclimate data suggest about the magnitude, timing and spatial patterns of past wet periods. I will then turn to efforts to interpret these paleoclimate data, exploring ways that we can compare data from ancient lakes with model output both to offer insights into past atmospheric dynamics and to test model performance in quite different climatic conditions. These data-model comparisons suggest that wet periods in the western U.S. may depend on both the presence of large ice sheets as well as links to the tropics, and that models may substantially underestimate the magnitude of past precipitation changes in the region.

About the Speaker

David McGee’s research focuses on understanding the atmosphere’s response to past climate changes. By documenting past changes in precipitation and winds using geochemical measurements of stalagmites, lake deposits and marine sediments and interpreting these records in the light of models and theory, he aims to offer data-based insights into the patterns, pace and magnitude of past hydroclimate changes. His primary tool is measurements of uranium-series isotopes, which provide precise uranium-thorium dates for stalagmites and lake deposits and allow reconstructions of windblown dust emission and transport using marine sediments.

About this Series

The PAOC Colloquium is a weekly interdisciplinary seminar series that brings together the whole PAOC community. Seminar topics include all research concerning the physics, chemistry, and biology of the atmospheres, oceans and climate, but also talks about e.g. societal impacts of climatic processes. The seminars generally take place on Monday from 12-1pm. Lunch is provided to encourage students and post-docs to meet with the speaker. Besides the seminar and lunch, individual meetings with professors, post-docs, and students are arranged.