INVESTIGATING BRGDGT SOURCES AND SEASONALITY IN PARADISE POND

In recent years, a group of bacterial membrane lipids called branched glycerol dialkyl glycerol tetraethers (brGDGTs) has emerged as a promising paleotemperature proxy in lake sediments. A relationship between temperature and the degree of methylation of these brGDGTs has been shown in numerous settings, but many questions regarding the sources and seasonality of these signals remain. Since brGDGTs may originate in either watershed soils or within the lake itself, it is necessary to determine the sources of these biomarkers in order to accurately reconstruct temperature from lake sediment cores. In many cases, this requires an in-depth analysis of brGDGTs in the lake and surrounding watershed soils. We chose to investigate the modern relationship between brGDGT production and temperature in our campus pond, Paradise Pond, Smith College in Northampton, MA. To do this, we collected soil samples from six locations around the pond, as well as surface sediment samples from the bottom of the pond in three different locations. The sample locations were chosen based on the bathymetry of the pond and our assessment of the catchment area. We will compare the concentrations and fractional abundances of brGDGTs in the catchment area soils and pond sediments to develop a profile of brGDGT production and soil input specific to Paradise Pond, and then apply various published calibrations to attempt to match the observed temperatures with the brGDGT signals. To investigate the seasonality of brGDGT production, we will additionally analyze samples collected from the same locations four months later. Although our interpretation will be specific to Paradise Pond, the data collected here will contribute to furthering the understanding of how to interpret brGDGT signals in lakes and ponds globally.