This study uses planktonic foraminiferal assemblages and SST proxy (transfer functions and alkenones) data from the Southern Benguela System, offshore the Cape of Good Hope to examine palaeoceanographic change at this important juncture of the thermohaline circulation. The records of watermass characteristics and variation thus derived are used to understand further climatic mechanisms and feedback within the Southern Hemisphere and globally. Various modes of surface circulation are associated with particular climatic intervals through statistical and ecological analysis of faunal census data. Transitions and early interglacials are associated with watermasses including a significant Indian Ocean component. The main feature of glacials is an eutrophic ocean environment interval (OEI) linked to increased upwelling and filament projection into the Cape Basin. Cooler stadials of interglacials are marked by increased abundance of transitional and oligotrophic species associated with the South Atlantic gyre. These environments are seen in a characteristic order through a typical glacial-interglacial cycle as watermasses respond to insolation changes and thermohaline and atmospheric reorganizations. These are driven by northern hemisphere summer insolation cycles through trade wind strength, ITCZ position, and the position of the Agulhas Retroflection. The South Atlantic gyre signal is determined by austral summer insolation, however. SSTs reconstructions provide a direct record of the changing temperature characteristic of regional watermasses and thus are a second constraint on the interpretations derived from planktonic foraminiferal assemblages. Two techniques are used in this study: faunal-based transfer functions (TFT); and alkenones (U<sup>k</sup>’<sub>37</sub>). Past interglacials were at least as warm as today, and during MIS 5.5 and 11.3 exceeded present values. U<sup>k</sup><sub>37</sub> SST records are generally similar to the TFT warm season temperatures, but during peak interglacials (MIS 9.3, 7.3 and 5.5) are an additional ~1.5°C warmer. This difference is ascribed to the sensitivity of the foraminiferal TFT to seasonal changes in upwelling and frontal movements.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:640145 |
| Date | January 2001 |
| Creators | Acheson, Ruth |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/10732 |
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