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



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-COproxies. I will assess the history of atmospheric CO2 across the Late Miocene through the first multi-proxy, multi-site study.




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.