Research
Whats the big deal about mud?
Lake sediments are excellent natural archives of the earth's history that can record information about climate, vegetation, aquatic ecology, biogeochemistry, geomorphology, hydrology, natural disasters, and human impacts to the environment. By combining geochronological information to determine the age of sediments with sedimentological, chemical and biological information, it is possible to reconstruct how environments varied over thousands of years. This information is neccesary to understand natural processes and variability. Without this "paleo" perspective it is very difficult to place current human-caused changes in proper context and it is also difficult to imagine or predict future changes.
Lake sediment geochronology
I use a variety of techniques to determine the age of sediments. Counting annual layers (varves) is the best way to get detailed age information at annual resolution. Therefore, lake sediments with varves preserved are incredibly valuable! For recent sediments (< 150 years), radioisotopes such as Pb-210 and Cs-137 are used. For sediments up to 50,000 years old, radiocarbon ages are the most commonly used dating method. Additional age information can come from tephra (volcanic ash) layers and other sources. I prefer to combine multiple sources of age information into Bayesian models to construct full chronologies for sediment cores (Zander et al, Quat. Geochronol., 2018; Zander et al, GChron, 2021).
Organic geochemistry
Organic chemistry can be applied to lake sediments to isolate specific organic molecules, called biomarkers, that can tell us about what types of organisms were living in or around the lake. Detailed studies of these molecules and their isotopic composition can provide extremely rich information about past climates and environments. In my research, I have used sedimentary pigments to reconstruct past algal and bacterial communities in lakes (Zander et al., Sci. Total Environ., 2021). Alkenones and GDGTs are both biomarkers that are sensitive to temperature changes and can be used as paleothermometers. Alkanes and fatty acids derived from plant waxes can provide information about organic matter sources and vegetation changes (Tierney et al, Geology, 2017). Furthermore, it is possible to measure isotopes of carbon (δ13C) and hydrogen (δD) on these waxes, which we use to investigate hydroclimate variability.
High resolution core-scanning techniques
Sediments slowly accumulate over time in lakes. In most lakes 0.1-10 mm of sediment may be deposited in a single year. This relationship between sediment depth and time means that the temporal resolution of any analysis depends on the sedimentation rate and the sampling interval. For many conventional chemical analyses, it is impractical to take samples at a resolution higher than every 10 mm. But these samples might integrate information over decades to centuries. New advances in core scanning technology make it possible to measure physical and chemical properties at ultra-high-resolution (0.05-0.2 mm), making it more feasible to study seasonal-scale phenomena in sediments. In my research, I have used hyperspectral imaging (Zander et al., J. Imaging, 2022) and micro X-ray fluorescence core-scanning to generate > 10,000 year-long records of lake trophic state and mixing regimes and other environmental factors (Zander et al., Sci. Total Environ., 2021). Additionally, I have used these methods to investigate in detail how weather conditions affect sediment composition at seasonal scale (Zander et al., Clim. Past, 2021).