Application of the Branched Glycerol Dialkyl Glycerol Tetraether (brGDGT) Temperature Proxy on Tropical Lake Bosumtwi in West Africa: Assessment of the Proxy and the Resulting 2,000 Year Paleotemperature Record



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Little remains known about the Holocene temperature history of West Africa, partly due to the fact that a paleoclimate proxy with the ability to reconstruct tropical temperatures has not been available. The branched glycerol dialkyl glycerol tetraether (brGDGT) biomarker provides the potential to reconstruct tropical temperatures using lake sediment cores. This study presents one of the first application of the brGDGT temperature proxy on a West African lake and produces one of the only late Holocene temperature reconstructions for the region. The brGDGT temperature proxy is applied to sediment cores sampled from Lake Bosumtwi, Ghana spanning 2,000 years. The resulting temperature reconstructions are temporally consistent with previously published reconstructions, however the magnitude of the reconstructed trends shows significant differences from previous studies. The reconstructions show LIA cooling of 4 +3°C and warming during the first half of the last century of 6 +3°C. Three different brGDGT calibrations are compared and the SFS calibration is found to produce the most reliable reconstruction. The reconstructions also show variability of 2-3°C, which is unexpectedly high based on the temperature trends in the instrumental record. The source of this discrepancy in magnitude and variability of temperature change remains unclear, but are hypothesized to be related to within-lake processes. The brGDGT proxy has the potential to provide powerful insight into the Earth’s temperature history, but the method needs improvement before high-resolution reconstructions are produced.



Holocene climate, Bosumtwi, brGDGTs, biomarkers, paleoclimatology, tropical paleoclimate