oa Heterocyte Glycolipids as Proxies for Nitrogen Fixation, Multicellularity and Continental Climate

Despite the need to understand past climate change in order to improve predictions of future changes, continental climate is difficult to reconstruct due to a lack of widely applicable paleotemperature proxies. Ratios of heterocyte glycolipids produced by heterocystous cyanobacteria ubiquitous in continental terrestrial and aquatic environments have great potential to capture paleotemperatures in continental sediment archives. To better understand glycolipid distributions and distangle potential proxy influences other than temperature, we provide the largest heterocyte glycolipid dataset of cyanobacterial cultures. We find a strong species effect that, in natural settings, appears to be largely cancelled out through averaging of lipid contributions from different cyanobacterial sources. Our data illustrates that additional culture and calibration studies are needed and that substantial shifts in cyanobacerial community composition should be investigated using not only glycolipid profiles but also e.g. hydrocarbon and fatty acid profiles or compound specific isotopes to allow selecting the most appropriate calibrations for paleotemperature reconstructions using the novel hterocyte glycolipid-based temperature proxies.