Abstract
Bulk-chemical (CORTEX) analyses of a transect of seven cores through the Southeastern Atlantic Ocean show that the variations observed in core MD962094 are characteristic for this part of the Atlantic Ocean (Chapter 2). Therefore, the physical properties of the terrigenous fraction of the sediments from this core will be studied.
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First, the quality of the laser particle sizer Malvern Mastersizer S will be examined. The combination of grain-size analyses and an end-member algorithm appears to be ideal for the analysis of mixtures consisting of several subpopulations (Chapter 3). The grain size of bulk sediments (predominantly composed of calcium carbonates) appears to be a good tool to reconstruct the carbonate dissolution on Walvis Ridge (Chapter 4). The interpretation of the downcore bulk size record as an upwelling-induced carbonate-dissolution record correlates well with the wind-strength record obtained from the grain size of terrigenous sediments on Walvis Ridge (Chapter 5). The end-member algorithm is also applied to the terrigenous fraction of the sediments from core MD962094. It appears that variations in the size distributions of the terrigenous fraction can be explained using three end members. These end members are interpreted as 'coarse' aeolian dust, 'fine' aeolian dust and fluvial mud. The interpretation of the end members from Walvis Ridge is supported by the end members that result from three time slices of sediments from the continental slope offshore Walvis Bay (Chapter 6). The ratio of the two aeolian end members is a measure of the size of the aeolian dust, related to wind strength. The proportion of aeolian dust versus fluvial mud is a measure of continental aridity. The continental-aridity record that can be derived from the terrigenous fraction of sediments from the SE Atlantic Ocean, correlates well with other palaeoclimate records from the Southern Hemisphere (Chapter 7). It appears that continental aridity in southwestern Africa can be related to changes in oceanic and atmospheric circulation patterns, probably driven by the Antarctic ice volume and associated sea-ice extent. The chemical and physical properties of the sediments from the Southeastern Atlantic Ocean are closely linked to each other (Chapter 8), therefore, great care has to be taken when interpreting bulk-chemical records. The bulk chemistry results from CORTEX, which seem to show a palaeoclimate record, are in fact predominantly caused by dissolution of calcium carbonate.
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