Palaeoceanographic variability in the South East Atlantic Ocean during periods of low orbital eccentricity

• Main Author: Dickson, A. J.
• Published: University College London (University of London) 2009
• Subjects: 550
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.625191

The Marine Isotope Stage (MIS) 11 interglacial has been considered to be analogous to the Holocene because of a similarity in the conditions of orbital forcing (low eccentricity and precession), but the role of climatic feedback processes linking orbital drivers to climate signatures is not well understood. This thesis examines palaeoceanographic sediment records from the South East Atlantic Ocean covering the last 50,000 years and the period encompassing MIS-11 (335-475 ka) to better understand how different facets of the climate systems were linked together in these two periods of low orbital eccentricity. It is shown that palaeoceanographic changes were closely linked to variations in Northern Hemisphere ice-volume via changes in the mode of the Atlantic Meridional Overturning Circulation (MOC). When ice-volume was high, a weaker MOC drove regional sea-surface warming and salinity increases; it also produced corresponding changes in the South African monsoon system by displacing the southern zone of Hadley Cell circulation over the study region. The interlinked nature of these connections makes it difficult to establish an ultimate driver; for example, a precession-pacing of monsoon and sea-surface temperature proxies during late MIS-11 could have been induced either by local (sub-tropical) insolation forcing or by precession-modulation of ice-sheet margins. A direct comparison between identical palaeoclimate datasets for the last 50,000 years and the MIS-11 interglacial suggests that the long duration of MIS-11 compared to subsequent interglacials may have arisen through a strengthening of oceanic heat transport during a period of high obliquity approximately 15,000 years into the interglaical optimum. Although several Atlantic Ocean records support this contention, refining this model will require the aquisition of more geographically diverse records with more precise chronological constraints than re currently available from the global ocean.