Marine sediments in four piston cores collected from the northwest African continental margin during Biogeochemical Ocean Flux Study cruise 53 (RRS Charles Darwin) were comprehensively studied using a wide range of physical sediment parameters and geochemical techniques. The objective of the study was to examine the Late Quaternary palaeoceanography of the Northwest African continental margin and determine changes in the climate of the north and central African continent over the past 600 kyr. In addition, the core sites formed a transect running SE-NW, enabling the spatial analysis of upwelling intensity and wind vigour proxies. Chronostratigraphy was determined by correlating planktic (<I>G.inflata</I>) and benthic (<I>C.wuellerstorfi</I>) oxygen isotope (δ<SUP>18</SUP>O) records with the SPECMAP records of Imbrie <I>et al</I>. (1984) and Martinson <I>et al</I>. (1987). Sediment accumulation rates are greater during glacial stages and generally decrease with distance from the continent. North and central African continental aridity variations are indicated by the Al flux records. The calcium carbonate records also approximate aridity fluctuations due to dilution by lithogenic dust supplied by the Harmattan and northeast Trade wind systems. These changes operate dominantly at the 41 kyr (obliquity) Milankovitch frequency cycle and display highest Saharan dust input and aridity during glacial stages. Zr/Rb, Ti/Al and Lithogenic Component Grain Size profiles indicate an increase in grain size, and hence wind vigour, during glacial stages and the stage 5 interstadials, and hence display a strong 23 kyr (precessional) component of forcing as well as at the 100 kyr (eccentricity) frequency band. The most distal core site in the transect is strongly influenced by the kaolinite-rich Harmattan wind supply, while the three more proximal cores are affected by dust input from the northeast Trade winds. A high-resolution calcium carbonate profile of another core in the transect confirms the presence of high-amplitude, high-frequency climatic perturbations (aridity changes) with mid-termination setbacks similar to the Younger Dryas event which is seen in many north Atlantic climate records. This high latitude climatic deterioration also influenced north African climate, resulting in increased aridity and wind vigour at approximately 11,000 years BP. Similar climatic conditions are noted over the last 7,000 years. A sawtooth pattern in the high-resolution calcium carbonate and Bulk Sediment Grain Size records implies that rapid increases in continental aridity were followed by gradual increases in humidity, and that the insolation-induced African climate system is decoupled from global (ice-volume) climate change operating at a glacial/interglacial timescale.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:657453 |
| Date | January 1995 |
| Creators | Matthewson, Alastair P. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15288 |
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