2019 Schlanger Fellow – Samuel Phelps

Samuel Phelps

Lamont-Doherty Earth Observatory

The Role of Atmospheric CO2 in Late Miocene Environmental Change: A Multi-Proxy Study

Abstract

The Late Miocene saw dramatic environmental change and ecosystem revolution. Sea surface temperatures dropped by 5-10°C from 10 to 6 Ma; grasses adapted to arid, low-CO₂ conditions expanded across the tropics and subtropics. Both are potential responses to declining CO₂. However, CO₂ estimates for this time period are limited, and most records suggest little to no change through this transition. Are estimates of CO₂ incorrect and plagued by poor assumptions, or do we not understand the coupling of CO₂ and climate? Here I propose to address this question with new state-of-the-art records from two marine paleo-CO₂ proxies. I will assess the history of atmospheric CO₂ across the Late Miocene through the first multi-proxy, multi-site study.

Biography

Born in Rhode Island and raised in Vermont, I developed an appreciation for the environment at an early age. Between my junior and senior undergraduate years, I carried out a summer research project at the Lamont-Doherty Earth Observatory and gained a passion for geochemistry and paleoclimate. My dissertation research focuses on reconstructing atmospheric CO₂ concentrations over the last ~15 million years using the stable carbon isotope ratios of long-chain alkenones and the mineral remains of coccolithophorid algae. With the Schlanger Fellowship, I will expand on my thesis research by estimating surface ocean pH and atmospheric CO₂ using boron isotope ratios of planktic foraminifera from the same sediment samples in which I have alkenone-based CO₂ estimates, providing a direct inter-proxy comparison.