IsoTalk

The IsoTalk project aims to advance our understanding of Isochrysidales algal bloom dynamics and community composition in mid-latitude lakes. Group I alkenones appear to be a very promising paleothermometer as they are mainly produced in spring, an almost unknown aspect of past climate while being a determinant for many ecosystems. To reconstruct and compare past lake temperatures on the Swiss Plateau with the Alps, we are targeting two freshwater lakes: Lake Greifensee and Lake St. Moritz (FIGURE) based on their Group I alkenone distributions. The overarching aim would be the development of a U-37-K temperature calibration for temperate lakes.

Our approach combines intensive fieldwork (FIGURE), culture experiments, lipid biomarker analyses, and molecular profiling (FIGURE). Through our high temporal resolution sampling employing both water samples and sediment traps, we will be able to track the timing and controls on the Isochrysidales blooms to better understand the signals that make it into the sediment (Work package 1 (WP1). In-situ calibrations and laboratory calibrations (WP2) will be developed.

What controls the diversity of Isochrysidales in Swiss lakes will be determined by (WP3), whereas the validity of paleotemperature reconstructions will be tested by comparing the last 150 years with meteorological data in (WP4). NIOZ researchers will focus on improving our understanding of the annual cycle of Group I Isochrysidales and alkenone production dynamics using long-read sequencing of SSU-LSU marker genes. This approach will be combined with environmental contextual data to characterize the variability in Isochrysidales across Swiss lakes and how they respond to various environmental parameters.