A >22,000 yr diatom record from the plateau of Zambia

Abstract

AbstractDiatoms and sediments were examined in a 530 cm core from Ishiba Ngandu, Zambia, a lake formed by gentle downwarping. Diatom zone D (>20 cal ka BP) was mostly sand with abundantAulacoseiraandEunotia, suggesting a shallow lake perhaps kept fresh by spring inputs and lake discharge, except during deposition of the lowermost 66 cm. Gyttja deposition between about 22 and 20 cal ka BP suggested a deeper lake and a wetter climate, perhaps because the Congo Air Boundary (CAB) was farther southeast relative to modern times. The next zone, zone C (about 20–19 cal ka BP), was sand with abundantAchnanthidiumandEunotiabut very few planktonic diatoms, apparently representing very shallow water and an arid period without the CAB. The gyttja and diatoms in zone B (19–4 ka) suggested an increase in moisture when the CAB returned. Zone A (4–0 cal ka BP) was dominated by the planktonicAulacoseira(>89%), suggesting an increase in wind-driven mixing. Uniquely, Ishiba Ngandu likely has been relatively moist since the last glacial maximum, matching pre-Holocene wetness in Botswana but not its Holocene aridity; evidently the climate here had switched to that of East Africa.