Application of GDGT-derived temperature proxies on Mt. Kenya

Abstract

Glycerol dialkyl glycerol tetraethers (GDGTs) are membrane lipids produced by archaea (isoprenoid GDGTs - iGDGTs) and bacteria (branched GDGTs - brGDGTs) in terrestrial and aquatic settings. Our study examines the relationship between GDGT distribution and environmental parameters in soils collected along Mt. Kenya to examine their applicability as paleotemperature and paleoelevation proxies. Both global and regional calibrations were tested on our dataset. brGDGT-derived temperature for Mt. Kenya linearly correlates with altitude and is consistent for all the calibrations although the derived temperature lapse rate (0.53 °C/100 m) along the mountain from the global soil calibration by [1] is consistent with gridded climate data (0.52°C /100 m) along this transect. This lapse rate is lower than the regional estimate of 0.70°C /100 m previously obtained in other altitudinal gradients (Mt. Rungwe and Mt. Kilimanjaro) from the same region. Although brGDGTs are considered as a robust paleoelevation proxy regionally, individual site performances may be unique to their environmental setting, geographic location and altitude. In addition, a poor linear correlation between altitude and iGDGT-derived TEX86, a rarely investigated proxy in soils, implies that there are many other factors not investigated here that affects its applicability in tracking temperature changes along altitudinal transects.