Dissertation Abstract
Orbital- and millennial-scale climate variability and seasonality in East Asia reconstructed using molecular paleoclimate proxies
Thomas, Elizabeth K 2014 http://www.acsu.buffalo.edu/~ekthomas/
Geological Sciences, Brown University (United States), 192 pp.
The question of how to interpret precipitation isotope records in East Asia is an ongoing debate and has implications for understanding climate dynamics in East Asia. I address this question by generating millennial- and orbital-scale leaf wax hydrogen isotope (δ2Hwax) records spanning a climate gradient in East Asia. Orbital-scale isotope- enabled transient climate model data demonstrate that temperature has a significant impact on orbital-scale precipitation isotopes throughout China. I use independent molecular temperature records to remove the effect of temperature from δ2Hwax, yielding records that reflect source area and transport history, two factors related to atmospheric circulation. These records suggest that the mechanisms that influence orbital-scale circulation differ by region. In southern China, circulation is controlled by Northern Hemisphere insolation with a minor influence of ice volume. In central China, circulation is more strongly influenced by ice volume due to proximity to the mid-latitude westerly winds, the strength of which is tightly linked to Northern Hemisphere ice volume. These results highlight the importance of considering temperature and regionally variable precipitation seasonality and source dynamics when interpreting East Asian precipitation isotope records.
A 32,000 year-long core from Lake Qinghai provides an opportunity to study the interaction of westerly and monsoon air masses on the northeastern Tibetan Plateau. I use δ2Hwax to distinguish between isotopically distinct source areas, and leaf wax carbon isotopes to reconstruct plant ecosystem changes. The cold, arid glacial period was dominated by westerly precipitation and by cold-adapted C3 plants. During the Lateglacial and early Holocene, higher summer insolation caused monsoon circulation to reach the northeastern Tibetan Plateau. The resulting warm, wet summers allowed warm- adapted C4 plants to thrive in this region. Millennial-scale cool, arid events superimposed on the deglacial warming and wetting were likely forced by North Atlantic freshwater pulses.
This suite of temperature and stable isotope paleoclimate records in East Asia enhances our understanding of climate and ecosystem dynamics on a range of time scales. When fully interpreted in terms of seasonality, temperature, and circulation, these records provide robust benchmarks for comparison with climate and ecosystem models.
A 32,000 year-long core from Lake Qinghai provides an opportunity to study the interaction of westerly and monsoon air masses on the northeastern Tibetan Plateau. I use δ2Hwax to distinguish between isotopically distinct source areas, and leaf wax carbon isotopes to reconstruct plant ecosystem changes. The cold, arid glacial period was dominated by westerly precipitation and by cold-adapted C3 plants. During the Lateglacial and early Holocene, higher summer insolation caused monsoon circulation to reach the northeastern Tibetan Plateau. The resulting warm, wet summers allowed warm- adapted C4 plants to thrive in this region. Millennial-scale cool, arid events superimposed on the deglacial warming and wetting were likely forced by North Atlantic freshwater pulses.
This suite of temperature and stable isotope paleoclimate records in East Asia enhances our understanding of climate and ecosystem dynamics on a range of time scales. When fully interpreted in terms of seasonality, temperature, and circulation, these records provide robust benchmarks for comparison with climate and ecosystem models.