PP11D-01
Coastal lake sediments from the southern Cape, South Africa – Implications for sea level and climate variations during the Holocene

Monday, 14 December 2015: 08:00
2012 (Moscone West)
Michael Wündsch1, Torsten Haberzettl2, Kelly L. Kirsten3, Stephanie Meschner4, Peter Frenzel5, Jussi Baade1, Gerhard Daut2, Roland Mäusbacher6, Thomas Kasper7, Lynne J Quick3, Michael E. Meadows3 and Matthias Zabel8, (1)Friedrich Schiller University of Jena, Jena, Germany, (2)Friedrich Schiller University of Jena, Physical Geography, Jena, Germany, (3)University of Cape Town, Department of Environmental and Geographical Science, Cape Town, South Africa, (4)Friedrich Schiller University Jena, Institute of Geosciences, Jena, Germany, (5)Friedrich Schiller University of Jena, Institute of Geosciences, Jena, Germany, (6)Friedrich Schiller University, Jena, Germany, (7)Friedrich-Schiller-University, Jena, Germany, (8)Univ Bremen, Bremen, Germany
Abstract:
Within the RAIN project (Regional Archives for Integrated iNvestigations) interdisciplinary investigations on climate evolution and environmental change in southern Africa during the Late Quaternary are being conducted. For this purpose, spatial and temporal variations of the three major rainfall zones covering South Africa (winter-, summer- and year-round rainfall zone) are studied using both marine and terrestrial archives. Here we present results inferred from sediment records from lakes Groenvlei and Eilandvlei located on the southern Cape coast within the year-round rainfall zone.

From Eilandvlei, a brackish lake that is connected to the Indian Ocean via an estuary, a 30.5 m sediment core was recovered. Reservoir-corrected radiocarbon ages reveal a continuous sedimentation and a maximum age of about 8,900 cal BP. This ultra-high-resolution record of environmental change during the Holocene represents a unique discovery for entire southern Africa. Geochemical data reveal different phases of marine and terrestrial sediment deposition throughout the covered time span. Hence, this record reflects changes in sea level, but also variations in terrestrial sediment transport and thus changing climatic conditions. The sediment core from Groenvlei, which today is isolated from the Indian Ocean, covers the past 4,200 cal BP. Sediments from this lake are predominantly composed of autochthonous carbonates. Mineralogical investigations reveal alternating deposition of calcite and aragonite/dolomite, pointing to variable Mg/Ca ratios and thus variations in lake water salinity. These changes can be linked to sea level variations as well as to changes in the precipitation/evaporation balance, and hence climate. Based on these results, the Groenvlei record reveals a decreasing marine influence and a trend from generally drier to wetter conditions within the last 4,200 yrs. Moreover, several layers of enhanced allochtonous input were detected in this record, which can be interpreted as documents of heavy rainfall events.

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