Linking catchment hydrology and ocean circulation in Late
Holocene southernmost Africa
Annette Hahn1, Enno Schefuß1, Sergio Andó2, Hayley C. Cawthraw3,4, Peter Frenzel5, Martin Kugel1, Stephanie Meschner5, Gesine Mollenhauer6, and Matthias Zabel11MARUM Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany 2Department of Earth and Environmental Sciences, University of Milano-Bicocca, Milan, Italy 3Geophysics Competency, Council for Geoscience, Cape Town, South Africa 4Centre for Coastal Palaeoscience, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa 5Institute of Earth Sciences; Friedrich Schiller University of Jena, Germany 6Alfred-Wegener-Institute, Bremerhaven, Germany
Received: 05 Oct 2016 – Accepted for review: 30 Oct 2016 – Discussion started: 03 Nov 2016
Abstract. Recent studies of the South African climatic system revealed a highly complex interplay of forcing factors on precipitation regimes. This includes the influence of the tropical easterlies, the strength of the Southern Hemispheric Westerlies as well as sea surface temperatures along the coast of the subcontinent. This study of a sediment core at the terrestrial-marine interface spanning a time interval of ~ 4 ka provides insights on the highly dynamic climatic system in southernmost South Africa. Several organic proxies sensitive to changes in climatic parameters like the distribution and isotopic composition of plant-wax lipids as well as indicators for sea surface temperatures and soil input give information on climatic changes during the investigated time period. Moreover, the micropaleontology, mineralogical and elemental composition of the sediments reflects the variability of the terrigenous input to the core site. The combination of downcore sediment signatures and a catchment-wide provenance study indicate that the Little Ice Age was characterized by relatively warm sea surface temperatures in Mossel Bay and arid climatic conditions favorable to torrential flood events sourced in the Gouritz headlands. In contrast, the so-called Medieval Climate Anomaly is expressed by humid conditions in the Gouritz River catchment with lower, but highly variable sea surface temperatures in the Mossel Bay area. The coincidence between humid climatic conditions and cooler sea surface temperatures has been attributed to a strengthened and more southerly anticyclonic circulation. In this climatic setting strong tropical easterlies supply Indian Ocean moisture to South Africa and at the same time Agulhas Bank upwelling pulses become more common due to an increase in Agulhas Current transport as well as alongshore southeasterly winds. These processes resemble the modern day oceanography in summer and can be conceptualized in a regional climate model.
Hahn, A., Schefuß, E., Andó, S., Cawthraw, H. C., Frenzel, P., Kugel, M., Meschner, S., Mollenhauer, G., and Zabel, M.: Linking catchment hydrology and ocean circulation in Late
Holocene southernmost Africa, Clim. Past Discuss., doi:10.5194/cp-2016-100, in review, 2016.