Ocean and land climate dynamics off southeast Africa during the late Pleistocene: A multi-proxy approach

• Main Author: Simon, Margit Hildegard
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Cardiff 2014
• Subjects: Indian; NADW; North Atlantic
• Online Access: https://archimer.ifremer.fr/doc/00499/61036/64443.pdf; https://archimer.ifremer.fr/doc/00499/61036/

The Agulhas Current transport of heat and salt from the Indian Ocean into the South Atlantic around South Africa (Agulhas leakage), can affect the Atlantic Meridional Overturning Circulation (AMOC) and, thus, influence global climate. Upper water column reconstructions in the southwest Indian Ocean over the past 100 kyr based on marine sediments from the core region of the Agulhas Current suggest that surface ocean temperature, salinity and planktonic foraminiferal assemblage records from the Agulhas Current exhibit high variability on orbital to millennial timescales. A high degree of similarity in this variability could also be identified in the Agulhas leakage records in the South Atlantic which suggests that changes in the Agulhas leakage can be partly explained by upstream variability in the Current itself. The results of a benthic stable isotope record from the southwest Indian Ocean over the past 270 kyr gives evidence that during glacial periods as well as during Northern Hemisphere Cold Stadials Southern Component Waters substituted for North Atlantic Deep Waters. The recorded hydrographic variability in the deep southwest Indian Ocean is explained in terms of a less vigorous AMOC exporting a reduced amount of NADW into the Southern Hemisphere and/or at shallower depth causing the observed changes in the deep water inventory. A multiproxy data and model integration approach reveals that phases of more humid southeast Africa climate were driven by southward oscillations of the Intertropical Convergence Zone and its associated rain belt over the past two glacial-interglacial cycles. Low-latitude summer insolation changes paced by orbital precession explain the long-term climate variability whereas abrupt climate oscillations in the northern high latitudes are the main driver for the observed millennial-scale wet phases. Southeast African climate variability seems to have been coupled, and anti-phased, with the East Asian Summer Monsoon during the late Pleistocene. Agulhas Current sea surface temperatures changes did not exert a primary control on southeast African hydrology.