UNDERSTANDING ENVIRONMENTAL CONTROLS ON BRANCHED GLYCEROL DIALKYL GLYCEROL TETRAETHER (BRGDGT) DISTRIBUTIONS IN KONGRESSVATNET, SVALBARD

Quantitative paleotemperature proxies are essential to properly contextualize ongoing climate change. Distributions of brGDGTs, bacterial lipids produced in many environments globally, have a strong relationship to temperature in lake sediment archives and hold great potential as a climate proxy. However, in some environments, brGDGTs also correlate with environmental conditions other than temperature, such as dissolved oxygen (DO), conductivity, and pH. The bacterial responses to these environmental stimuli can confound the temperature signal generated by brGDGT calibrations. Additionally, different bacteria may respond to the same environmental stimuli by producing different brGDGTs, further clouding calibration attempts. This leads to the question of whether accurate brGDGT temperature reconstructions are possible to obtain in all environments around the world, or if a specific set of environmental requirements needs to be met to ensure a verifiable reconstruction.

To assess this question, we have studied Kongressvatnet, a lake in Arctic Svalbard. We have collected two years of bacterial DNA data and four years of brGDGT sediment trap data alongside conductivity, DO, and temperature data, all of which spans the water column. Kongressvatnet is 55 m deep, meromictic, and stratified. In the summer, it has chemoclines at 12 and 44 m, an oxycline at 35 m, and a thermocline at 10 m. Preliminary DNA data shows different bacterial communities throughout the lake water column, with low concentrations of acidobacteria, a known producer of brGDGTs. Additionally, the sediment traps show changing brGDGT compositions across the oxy- and chemoclines that can not consistently reconstruct accurate air temperatures. This lack of consistency indicates that temperature may not be the controlling environmental stimuli for brGDGT response in this lake. Our results have important implications for researchers utilizing this proxy across the globe.