Document Type

Dissertation

Abstract

The Middle Miocene Climate Optimum was a unique warming period in the Earth’s geologic history, when a high global mean annual temperature was accompanied by a relatively low global CO2 concentration. Hydrogen isotopic signals (specifically molecular δD, the ratio of deuterium to hydrogen) from lipids of fossils and sediments offer intrinsic insights into precipitation of ancient climates. Using samples collected from known Middle Miocene deposits, we measured δD of n-alkanes extracted from well-preserved plant and sediment samples from varying latitudes across the Northern Hemisphere, and then analyzed the data through a zonally averaged precipitation and evaporation climate model. The reduced latitudinal temperature gradient with warm polar regions during the Middle Miocene was also contrarily coupled with a small variance in latitudinal meteoric water composition and precipitation. With our latitudinally variant sample locations (ranging from 24°N in Xianfeng, China, to 74°N in Banks Island, Canada), we developed a one-dimensional model in which we assessed evaporation and precipitation gradients throughout the Northern Hemisphere. Ultimately, we used the latitudinal distribution of δD to better constrain the atmospheric conditions during the Middle Miocene Climatic Optimum.

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