My research focuses on developing and applying new organic geochemical tools to reconstruct past environmental conditions. My work contains many facets, including empirical calibrations, experiments designed to test the mechanistic underpinnings of my proxies, and applications to sediment cores. I have made particular use of compound specific hydrogen isotopes of lipid biomarkers, including triterpenoids and sterols.
MACRO: Molecular traces of Anthropogenic and Climatic impact in Remote Oceania – Funded by Swiss National Science Foundation Assistant Professorship to Dr. Nathalie Dubois
We are using lipid biomarker distributions and stable isotope ratios in sediment cores collected from lakes and swamps on islands throughout the western tropical Pacific to reconstruct the early environmental impacts of initial human settlers and the influence of climate on their activities. In the summer of 2017, we traveled to Vanuatu to collect plant samples and sediment cores from lakes and swamps. We are using these samples to develop new biomarkers for agriculture plants, to reconstruct past changes in climate and vegetation, and to assess how people changed soil erosion rates. The islands of Vanuatu were only settled within the last 3000 years, and these records will allow us to better understand the interplay between humans, climate, and the environment in a system constrained by both space and time.
Hydrogen isotope response of algal lipids to variable nutrient concentrations in Swiss lakes – Funded by NSF Earth Sciences Postdoctoral Fellowship
Eutrophication (nutrient pollution of lakes and other aquatic ecosystems) is commonly caused by fertilizers and detergents. It can result in harmful algal blooms and widespread fish death, and reduces the economic and aesthetic value of water bodies. The Swiss government has been especially proactive about reducing the causes of eutrophication and remediating polluted lakes. However, despite concerted efforts over the past thirty-five years, a range of nutrient concentrations persists among lakes in the central Swiss plateau. This project studies the impact of elevated phosphorus availability on lipid distributions and isotope composition in algae growing in Swiss lakes by analyzing surface sediment, sediment traps, and suspended particles from ten lakes in central Switzerland with different histories of nutrient loading. A follow-up to this project was recently funded through ETH’s postdoc career seed grant program, and is applying the results from our Swiss lakes study to a sedimentary record from Lake Greifen, spanning a well-documented period of eutrophication and partial recovery.
Quantitative Salinity & Water D/H from Paired H & C Isotopes in Mangrove Lipids – Funded by NSF Geobiology and Low-Temperature Geochemistry
Mangroves are woody trees that have adapted to live in brackish and saline water. They are prominent on coastlines throughout the tropics and subtropics and form extremely productive ecosystems. Although they cover only a small portion of the globe, mangroves play an outsized role in the global carbon cycle, and are responsible for up to 15% of the organic carbon stored in marine sediment. This means that organic biomarkers from mangroves are abundant in tropical and subtropical coastal sediments, and that lipids from these plants can provide important insights on environmental change at low latitudes.
My PhD research established a new tool for reconstructing past salinity and rainfall rates using the stable hydrogen and carbon isotope ratios of mangrove lipid biomarkers. This proxy is applicable to coastal lakes, swamps, and near shore sedimentary deposits in the tropics, and is based on systematic changes in the isotopic ratios of mangrove biomarkers with salinity. In collaboration with Prof. Julian Sachs and other researchers at the University of Washington, I continue to investigate the mechanisms responsible for these relationships through a combination of field and greenhouse based studies.
The National Science Foundation (NSF) has funded much of my research and I am very grateful for their support. However, any opinions, findings, and conclusions or recommendations expressed in this material are mine and do not necessarily reflect the views of the National Science Foundation.