Research
The Earth’s climate has always changed through time. Yet modern climate has a distinct human “fingerprint.” How can we be so sure? In part, study of the past guides our understanding of modern climate and environmental variability. We investigate past climate and environmental change to better understand the drivers of terrestrial and aquatic variability through time. In the MAB Lab, we specialize in molecular paleoclimatology, studying the fossilized remains of organic matter found in soils, rocks, and sediments from lakes and oceans. These organic molecules, called biomarkers, can be preserved for millions of years and can be linked to source organisms with different habitats and behaviors, manifested in their chemical composition. Our research often focuses on questions of past temperature, precipitation, and landscape change, using molecular and compound specific stable isotope proxies as valuable tools to quantify environmental change, from high latitudes to the tropics, recent to millions of years ago. We also conduct modern proxy development and calibrations to improve uncertainty in geologic reconstructions of parameters such as precipitation, bridging a critical gap between biomarker use, understanding the information recorded in our proxies, and how that signal is incorporated into the geologic record.
Research Highlights
Southern Ocean Fronts
The International Ocean Discovery Program (IODP) Expedition 361 (Southern African Climates) focused on the Agulhas Current, a critical component of ocean circulation, moving warm, saline waters in the Mozambique Channel, around the southern African “gateway.” We sailed on Exp. 361 and are working on a series of projects (Pliocene – present) to generate biomarker records of sea surface temperature, marine primary productivity, and salinity south of Africa (Site U1475). We are exploring global circulation variability and frontal migrations, with implications for Southern Ocean expansions, iceberg distributions, and ocean CO2 uptake. See recent publications: Starr et al., 2021; Tangunan et al., 2021; Cartagena Sierra et al., 2021.
Eastern African Paleoclimate
Often referred to as the ‘engines of the global water cycle,’ the tropics are particularly important places to reconstruct past climate, as they are the origin of global heat redistribution. We work on a variety of marine and lacustrine sites around eastern Africa to examine the spatial heterogeneity of climate variability, landscape change, and climate drivers. We are generating multiproxy biomarker records to reconstruct hydroclimate, temperature, terrestrial vegetation and burning, and aquatic community changes from sediment archives spanning the Late Miocene – present. We are also interested in exploring the climate/environment relationship to hominin evolution and migrations as well as the influence of more recent climate patterns on society. See recent publications: Koutsodendris et al., 2020; Taylor et al., 2021
Neotropical Paleoclimate
Lake Petén Itzá (Guatemala) represents a key spatial node for understanding climate variability between the equatorial tropics and subtropical North America. We are creating biomarker reconstructions from drill core sediments, and examining the mechanisms driving regional climate using proxy-model comparison work. These records will improve our understanding of tropical to high latitude linkages in the evolution of Neotropical climate during the Pleistocene. We have also begun new work on sediments from Lake Izabal (Guatemala) that will serve as a nearby site to explore regional climate variability. (Photo: J. Obrist-Farner)
Mediterranean Paleoclimate
The eastern Mediterranean region has a well-established record of hominin inhabitance and dispersal, with a climate sensitive to both high and low latitude dynamics. We are investigating the role environment and climate variability in the region may have played in hominin dispersal to Eurasia and in shaping early Mediterranean civilizations. Further, we are using biomarkers to explore how sensitive aquatic and terrestrial ecosystems may have been to hominin occupation and societal upheaval in the region. Using sediment cores from the Aegean and Adriatic seas, and from Greece, we are examining eastern Mediterranean climate and environmental variability from the Pleistocene – present.
Biomarker Proxy Development and Calibration
With no direct measurements of past precipitation, we use the δD of leaf waxes to study past water cycle variability. The utility of this proxy is rooted in our mechanistic understanding of the modern water cycle and what “translation” the proxy provides, helping to parameterize uncertainty in sedimentary leaf wax δD reconstructions of past precipitation. Our work is aimed at unraveling the biological and environmental factors that influence the leaf wax δD from the isotopic signature of precipitation. We are examining high latitude settings (see recent publications: Berke et al., 2019; O’Connor et al., 2020) and are beginning new work on eastern African tropical vegetation and precipitation. We are also working to refine microbial membrane lipid proxies, using soils, precipitation, and collected environmental variables.
We would like to thank the National Science Foundation, USSSP-IODP, Indiana Water Resources Research Center/USGS, Clare Booth Luce Foundation, the Geological Society of America, the Notre Dame Environmental Change Initiative, and the Notre Dame Center for Environmental Science and Technology for financial support that has made our research possible. This work would also not be possible without the support of our collaborators, some of whom are coauthors in existing publications.