FINDING HIGHLY-BRANCHED ISOPRENOID LIPID PRODUCING DIATOMS IN LAKE SUPERIOR AND THE ENVIRONMENTAL CONDITIONS THAT INFLUENCE THEIR PRODUCTION

In the Arctic and Antarctic, paleo sea ice extent has been quantified through the use of highly-branched isoprenoids (HBIs), a membrane lipid of diatoms. Diatoms, a single-celled algae with a silica cellular membrane, can be found in every aquatic ecosystem around the world. Species of benthic diatoms that grow on sea ice (commonly known as sea ice algae) produce specific congeners of HBIs, making them robust markers for previous sea ice extent in polar regions. More recent work has documented the presence of these compounds in both marine and freshwater systems. Our group has recently located “hotspots” of significant HBI lipid production in local small lakes and on the shores of Lake Superior, and we are exploring the potential of these lipids for use as paleo markers of lake ice extent in the great lakes region. However, the purpose of HBIs in the diatom lipid membrane, and therefore the environmental conditions that spur the synthesis of HBIs in diatoms, are not well known. Here, we present the results of a year-long study in an enclosed pool on the shore of Lake Superior near Two Harbors, MN, where diatoms are known to produce significant amounts of HBIs. Water temperature and nutrient concentrations are presented as well as the HBI concentrations from diatom mats collected monthly during 2019.