Anoxic in situ production of bacterial GMGTs in the water column and surficial bottom sediments of a meromictic tropical crater lake: Implications for lake paleothermometry

Branched glycerol monoalkyl tetraethers (brGMGTs) are membrane-spanning lipids which were initially identified in marine settings and have more recently been found peats lake sediments. In the latter settings, their abundance relative to that of branched dialkyl (brGDGTs) appears increase under warmer climate conditions. Furthermore, distribution bottom sediments from an altitudinal transect East African lakes has linked local mean annual air temperature (MAAT). To shed light on sources identify potential environmental factors driving production lakes, we investigated occurrence water column, surficial lake-bottom sediments, catchment soils Lake Chala, a permanently stratified (meromictic) tropical crater Africa. Data column comprise both suspended particulate matter (SPM) collected monthly at eight depth intervals between 0 80 m for 17 consecutive months, settling particles 35 over period 53 months. soils, brGMGTs either relatively scarce or absent. is dominated by four seven known mostly limited anoxic zone. Whereas spatial concentration SPM strongly influenced seasonal cycle strong water-column stratification alternating with deep mixing, this trend not consistent multi-year timescale settling-particles record. Moreover, did respond variation during studied interval. contrast contain full suite distinct spatially uniform fractional abundance, suggesting majority brGMGT takes place there. BrGMGT-inferred MAAT Chala area reasonably estimates measured conforms calibration. Our results important implications use as proxy MAAT, outside equatorial zone presumably greater offset bottom-water may create bias towards cold-season temperature. Regardless, singular source advantage paleotemperature reconstruction compared brGDGTs, several studies now indicate mixed aquatic terrestrial contribution cannot easily be disentangled assumed constant through time.