Janet working in the lab, washing and sieving forams from tropical Atlantic sediment cores. Inset: Close-up of coarse fraction slurry in a 150mm sieve.
Important changes in human evolution in Africa during the Pliocene-Pleistocene seem to be mediated by changes in African climate or shifts in climate variability. By reconstructing the development of the tropical Atlantic sea surface temperature (SST) gradientfrom 3.5 Ma up to the present, we provide another constraint on the paleoenvironment of hominin evolution. Evidence gathered from geochemical analyses of the planktonic foraminifer, Globigerinoides ruber, yield a zonal reconstruction that shows the tropical SST trend and variance to be consistent with paleoclimatic records that indicate African aridification since the Pliocene; this signifies a link between SSTs and African climate.
Photo micrograph of G. ruber foram.
Used with permssion from Dr. Eelco J. Rohling. http://www.soton.ac.uk/~bam2/col-index/fossi-lindex/Forams/Eelco/red-sea/index.htm
An enhancement of the tropical Atlantic SST gradient and an increase in SST variability occurred around 2.7 Ma. Though gradual, this shift is contained within a narrow range and is coincident with shifts in African dust, soil carbonate d13C, plant wax biomarkers, and benthic d18O, and even corresponds with some junctures in the climate-forced evolution of our ancestors.
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Last updated: 8 January 2001, KAK.