5 Paleoclimate I (Posters)

Thursday, 24 July 2003
1:30 PM - 4:30 PM

LATE QUATERNARY ENVIRONMENTAL CHANGE ON THE AGULHAS PLAIN, WINTER RAINFALL ZONE, SOUTH AFRICA

Paper number: 5-30
Program: Technical Sessions
Time: 1:30 PM – 4:30 PM

Authors

Abstract

Despite its key position, at the interface of the temperate westerly and tropical climatic systems, the Quaternary environmental record in South Africa’s winter rainfall zone is poorly resolved. Little is known of its relationship to the larger summer rainfall zone, particularly in terms of the synchronicity and direction of past climatic changes. At the southern most tip of Africa and the meeting point of the Agulhas and Benguela currents, the Agulhas Plain represents a winter rainfall zone area that was potentially very sensitive to Quaternary environmental change. Four pan/lunette dune complexes have been investigated in this area and a chronology of lunette deposition derived from 17 OSL age determinations has produced a record spanning the last 70 ka. The study has also involved the extraction of cores from littoral environments on the floor of Voelvlei pan, the aim being to utilise independent, but complementary proxy data sources from the same site; an “arid” or aeolian record derived from the lunette dune and a “humid” record of pan water status from the core sediments.

Inadequate optical bleaching hampered attempts at OSL dating of sand units in the cores, but radiocarbon dating of fine grained, pollen rich units produced an age of c. 28 ka BP (uncal). It is suggested that these units are associated with pelagic environments and represent high water conditions. This radiocarbon age contrasts with a suite of OSL ages for the lunette dune, which indicate two discreet phases of lunette deposition (17 -23 Ka and c. 3 Ka). OSL ages obtained from nearby Soutpan and Rhenosterkop pan suggest lunette deposition during OIS 4. A small fourth pan (Buffeljacht pan), c. 30 km further west also indicates lunette deposition during the late Holocene. The disparate timing of lunette deposition for sites within 30 km of each other may be explained by the contrasting geological and hydrological settings of the pans. However, it appears that much lunette deposition on the Agulhas Plain has been associated with OIS 4 and 2 and thus hypothermal conditions. The orientation of these lunette dunes, all on the eastern shores of the pans, indicates westerly formative winds and contrasts with the dominantly easterly winds of the modern dry season.