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Title: Late Quaternary palaeoceanography of the Benguela upwelling system
Author: Little, Mark G.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1997
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Planktonic foraminifera recovered from nine cores in the Benguela Current system are used to ascertain the variability of upwelling intensity for the Late Quaternary and its impact on atmosphere-ocean-cryosphere linkages. The analyses from high-resolution planktonic foraminiferal records for cores GeoB 1706, GeoB 1711 and PG/PC 12, reveal striking variations in upwelling intensity during the last 160,000 years. Four species make up over 95% of the variation within the cores, and enable the record to be divided into episodes characterised by particular planktonic foraminiferal assemblages which have meaningful ecological significance when compared to those of the present-day and the relationship to their environment. The cold-water planktonic foraminifer, Neogloboquadrina pachyderma sinistral [N. pachyderma (s))], dominates the modern-day, coastal upwelling centres, and Neogloboquadrina pachyderma dextral and Globigerina bulloides characterise the fringes of the upwelling cells. Globorotalia inflata is representative of the offshore boundary between newly upwelled waters and the transitional, reduced nutrient levels of the sub-tropical waters. In the fossil record, episodes of high N. pachyderma (s) abundances are interpreted as evidence of increased upwelling intensity and the associated increase in nutrients. The N. pachyderma (s) record suggests rapid shifts in the intensity of upwelling, and corresponding trophic domains, that do not follow the typical glacial - interglacial pattern, but instead reflect the shifts of the Angola-Benguela front situated to the north of the Walvis Ridge. Absence of high abundances of N. pachyderma (s) from the continental slope of the southern Cape Basin indicate that Southern Ocean surface water advection has not exerted a major influence on the Benguela Current system. The periods of high abundance in N. pachyderma (s) are referred to as 'PS events' and indicate increased intensity and zonality of the South Atlantic trade winds controlling the Benguela upwelling system. During these intense upwelling phases, total organic carbon, abundance of N. pachyderma (s) and the benthic/planktonic foraminiferal ratio, provide the best indicators for palaeoproductivity away from coastal re-suspension. The offshore record of GeoB 1711 is used as the indicator for maximum offshore divergence and shelf-edge upwelling and is regarded as the best indicator for palaeoceanographic and palaeoproductivity variability.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available