UNDERSTANDING THE MIDDLE MIOCENE CLIMATIC OPTIMUM: EVALUATION OF DEUTERIUM VALUES (ΔD) RELATED TO PRECIPITATION AND TEMPERATURE

The Middle Miocene Climate Optimum represents a unique warming period in the Earth’s history when a high global mean temperature was accompanied by a relatively low global CO₂ concentration. However, the global precipitation gradient during the time is poorly understood. Hydrogen isotopic signals (specifically molecular δD) from fossils and sediments offer insight into intrinsic precipitation data of ancient climates. Using Middle Miocene samples, we measured δD from n-alkanes extracted from well-preserved plant fossils and sediments of varying latitudes across the Northern Hemisphere, then analyzed the data through a zonally averaged precipitation and temperature climate model. The reduced latitudinal temperature gradient with warm polar regions during the Middle Miocene is also contradictorily coupled with a small variance in latitudinal meteoric water composition and precipitation. With our 12 latitudinally variant sample locations (ranging from 24°N in Xiangfeng City, China, to 74°N in Banks Island, Canada), we are able to develop a one-dimensional zonally averaged model of meridional water vapor in which we infer the impact of a reduced temperature gradient on precipitation throughout the Northern Hemisphere. This on-going research project will establish a latitudinal precipitation trend which will be compared to established temperature data in order to determine the extent of dependence of the two variables. Correlation detected in our independent model will be used to search for other factors involved in the forcing of the Middle Miocene Climate Optimum, ranging from continental effect to CO₂ levels.