Articles | Volume 13, issue 6
Clim. Past, 13, 649–665, 2017

Special issue: Southern perspectives on climate and the environment from...

Clim. Past, 13, 649–665, 2017

Research article 09 Jun 2017

Research article | 09 Jun 2017

Southern Hemisphere anticyclonic circulation drives oceanic and climatic conditions in late Holocene southernmost Africa

Annette Hahn1, Enno Schefuß1, Sergio Andò2, Hayley C. Cawthra3,4, Peter Frenzel5, Martin Kugel1, Stephanie Meschner5, Gesine Mollenhauer6, and Matthias Zabel1 Annette Hahn et al.
  • 1MARUM – 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, Jena, Germany
  • 6Alfred Wegener Institute, Bremerhaven, Germany

Abstract. Due to the high sensitivity of southern Africa to climate change, a reliable understanding of its hydrological system is crucial. Recent studies of the regional climatic system have 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. However, very few marine records have been available in order to study the coupling of marine and atmospheric circulation systems. Here we present results from a marine sediment core, recovered in shallow waters off the Gouritz River mouth on the south coast of South Africa. Core GeoB18308-1 allows a closer view of the last  ∼  4 kyr. Climate sensitive organic proxies, like the distribution and isotopic composition of plant-wax lipids as well as indicators for sea surface temperatures and soil input, give information on oceanographic and hydrologic changes during the recorded time period. Moreover, the micropaleontology, mineralogical and elemental composition of the sediments reflect the variability of the terrigenous input to the core site. The combination of down-core sediment signatures and a catchment-wide provenance study indicate that the Little Ice Age ( ∼  300–650 cal yr BP) was characterized by climatic conditions favorable to torrential flood events. The Medieval Climate Anomaly ( ∼  950–650 cal yr BP) is expressed by lower sea surface temperatures in the Mossel Bay area and humid conditions in the Gouritz River catchment. These new results suggest that the coincidence of humid conditions and cooler sea surface temperatures along the south coast of South Africa resulted from a strengthened and more southerly anticyclonic circulation. Most probably, the transport of moisture from the Indian Ocean by strong subtropical easterlies was coupled with Agulhas Bank upwelling pulses, which were initiated by an increase in Agulhas Current strength.

Short summary
Our study demonstrates that a source to sink analysis in the Gouritz catchment can be used to obtain valuable paleoclimatic information form the year-round rainfall zone. In combination with SST reconstructions these data are a valuable contribution to the discussion of Southern Hemisphere palaeoenvironments and climate variability (in particular atmosphere–ocean circulation and hydroclimate change) in the South African Holocene.