The quest for new lipid biomarkers in suspended particles in the water column of Lake Chala, tropical East Africa, and their potential as paleoenvironmental proxies

Abstract

An inventory of lipid biomarkers in suspended particulate matter (SPM) from Lake Chala, a meromictic crater lake, was made, and then coupled to physical changes within the lake water column. Diatom blooms, which occur during periods of deep mixing were found to be reflected by compounds such as (iso)loliolide, methyl-9,10-dihydroxyoctanoate and 23-methylcholesta-5,22-dienol. A aglycone triol, 1,3,25-hexacosanetriol, was found to covary with a C19:1 alkene that was previously linked to the occurrence of cyanobacteria. The majority of sterols, even though they form the most abundant group of lipid biomarkers within Lake Chala, are not exclusively indicative of a singular variable within the lake. Their signal appears to be a combined signal of influx of plant material from within the crater and in-situ production by organisms in the water column. The same applies for three n-alkanols (tetra-, hexa- and octadecanol), however based on their short chain length, a phytoplankton source is still the most probable major source. Lastly, two diols, 2,23-C24 diol and 2,25-C26 diol were found predominantly in the anoxic region of the lake, extending to the surface during deep mixing. Although their producing organisms are unknown, previous studies have linked their occurrence to anoxic conditions.