Degree

Doctor of Philosophy (PhD)

Department

Geology and Geophysics

Document Type

Dissertation

Abstract

Compound-specific stable isotope analysis and biomarker-based paleothermometry have been increasingly applied to for paleoclimate and paleoecology studies. The first project aims to reconstruct the paleoclimate in the Qaidam Basin during the last glacial period. Qaidam Basin in the Northern Tibetan Plateau is a critical eolian factory located at a unique geographic location that links the Westerlies and the Asian summer monsoons. However, how the interactions of two climatic systems influence the paleohydrology that in turn impacts the eolian production in the Qaidam Basin has been seldom explored. Our compound-specific hydrogen isotope and UK 37 temperature data found that the Westerlies and Asian summer monsoons alternately controlled the Qaidam Basin’s climate in response to precessional forcing during the late Pleistocene. The second project studies the hydrological change in the Gulf of Mexico (GoM) region during the “greenhouse” to “icehouse” transition near the Eocene-Oligocene boundary (33.9 Ma). The geological evidence and climate model proposes that cooling in the Northern Hemisphere was delayed and weaker than in the Southern Hemisphere during the climate transition, which intensifies the Atlantic Meridional Overturning Circulation, increased precipitation in low-latitudes, and subsequent drawdown of atmospheric carbon dioxide during weathering processes. However, there are no quantitative constraints on variations in low latitude precipitation during this interval. Our paleoclimate data from the GoM through the climate transition interval (33.45 – 34.13 Ma) show increased precipitation up to 50%, supporting the CO2- weathering feedback hypothesis and highlighting the low-high latitude climate and atmospheric-oceanic connectivities. The third project focuses on the post middle Miocene paleoclimate and ecological change in the northern Tibetan Plateau (TP). The relative importance of high topography on the TP and the global cooling in regional climate and ecology in Central Asia has been a longstanding debate. Our carbon isotope records from Hexi Corridor, northern TP (spanning from ca. 16 Ma to 2 Ma) show that (1) global cooling plays a primary role in the decline in C4 plant contribution in northern Tibetan Plateau since the ~14.8 Ma, and (2) the disparate regional climate patterns in northern Tibetan Plateau since ~12 Ma are owing to the uplift of plateau.

Committee Chair

Zhuang, Guangsheng

Available for download on Wednesday, February 02, 2022

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