New AMS dates, stratigraphic correlations and decadal climatic cycles for the past 4 ka at Lake Turkana, Kenya

Abstract

New AMS radiocarbon dates and stratigraphic correlations of 7 piston cores recovered from Lake Turkana, East Africa, show that the frequency of cyclic variability is greater than previously reported for a single piston core. Almost 60 new AMS dates of various carbonate fractions indicate that large (150 μm) ostracode carapaces yield the most accurate chronology for the sediment record due to the input of “old” fine-grained carbonate. Stratigraphic correlations among the cores by carbonate abundance and magnetic susceptibility profiles provide supporting evidence for the ostracode-based chronology. This chronology refines earlier estimates of sediment accumulation that impacts the recurrence interval of lamination deposition from one lamination every two years to one lamination per year in two north basin cores. The record of carbonate content within the north basin of the lake reflect its dilution with terrigenous sediments input from the Omo River but direct paleoclimatic interpretations are complicated by lateral migrations of the delta channels with changing lake levels. Time-series analysis of both individual cores and a combined carbonate profile show significant spectral peaks at 1000, 76, 32, 22, 18.6 and 11 yr. The latter three suggest an important link between the sediments accumulating in Lake Turkana and global cycles of climatic variability.