The idea that human activity is driving recent global climate change has gained scientific consensus and entered the public spotlight. It is up to scientists such as paleoclimatologists to understand the nature of climate change and how the activities of people might affect it. The goal of paleoclimatology – the study of past climates – is to expand our record of climate change and help us understand what the future holds.
One of the most hotly debated topics in paleoclimatology has been the ice age climate record of the Great Basin region of the western US over the past ~500,000 years. A new stalagmite-based record of climate change in the Great Basin region constructed by Lachniet et al. (2014, Nature Communications, 5, 4805) seems to have solved this controversy, but it only extends back 175,000 years. The aim of our research is to help extend this record through a coupled petrographic and high-resolution stable isotopic analysis of a stalagmite that grew discontinuously in Lehman Caves, Nevada between ~650,000 and 243,000 years ago.
High-resolution stable isotope analyses drilled up to and across growth hiatuses in this stalagmite reveal that the oxygen isotope value becomes progressively more negative (the ratio of 18O to 16O decreases) towards the termination of the hiatus. This trend is interpreted to be the result of a consistent change in the processes that control the oxygen-isotope value of dripwater in Lehman Caves, such as a shift in the dominant sources of precipitation. The carbon isotope value (the ratio of 13C to 12C) exhibits less consistency at the hiatuses, however, and may reflect multiple effects such as variations in vegetation density or soil water residence times. Overall, petrographic and high-resolution stable isotope data of the stalagmite may offer an additional method of deciphering climate change that wasn’t possible with a typical stable isotope analysis.
Christopher Felt, ’16
Sponsor: Rhawn Denniston