A petrographic and geochemical record of climate change over the last 4600 years from a northern Namibia stalagmite, with evidence of abruptly wetter climate at the beginning of southern Africa's Iron Age

Abstract

Stalagmite DP1, a speleothem 1.6m in length from Dante Cave in northeastern Namibia, provides a paleoclimate record of a gradual transition from wetter to drier conditions from 4.6 to 3.3kaBP, a variable but pronounced dry period from 3.3 to 1.8ka, and a wetter but variable period from 1.8ka to the present. This record is based on 30U/Th radiometric dates and their resulting calculated growth rates, and on C and O stable isotope data, relative proportions of aragonite and calcite in layers, measurements of stalagmite width along layers, and observation of petrographic surfaces suggestive of changes from drier to wetter conditions and vice versa.The stalagmite's first deposition, which seemingly followed conditions too wet for deposition, coincided with desiccation in the Sahara and the end of the African Humid Period there. Gradual drying continued and led to a sustained very dry period from 3322±11 to 1786±10BP, a “2–3kaBP Dry Period”. That dry period began and ended abruptly.The abrupt transition from drier to wetter conditions at 1.8ka coincides with the beginning of the Iron Age in southern Africa, suggesting that wetter conditions facilitated migrations and/or changes in food production that may have contributed to a transition in human technologies and lifestyles. This transition is coeval with transitions to colder conditions in ice core records from Greenland and Antarctica.The DP1 record suggests considerable change over the past 1800years, with at least three wet/dry cycles. The wettest conditions may have occurred relatively recently, between 230 and 100BP (A.D. 1720 and 1850), so that early European explorers may have seen and/or heard reports of conditions among the wettest during the later Holocene in southern Africa.