Glacial/interglacial changes in southern Africa: Compound-specific [delta] super(13)C land plant biomarker and pollen records from southeast Atlantic continental margin sediments

• Published in: Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2006-08, Vol.7 (8), p.np-np
• Main Authors: Rommerskirchen, Florian, Eglinton, Geoffrey, Dupont, Lydie, Rullkotter, Juergen
• Format: Article
• Language: English
• Subjects: Basins; Deserts; Indicators; Plants (organisms); Pollen; Sediments; Signatures; Vegetation
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2005GC001223

This is part 2 of a study examining southwest African continental margin sediments from nine sites on a north-south transect from the Congo Fan (4 degree S) to the Cape Basin (30 degree S) representing two glacial (MIS 2 and 6a) and two interglacial stages (MIS 1 and 5e). Contents, distribution patterns, and molecular stable carbon isotope signatures of long-chain n-alkanes (C sub(27)-C sub(33)) and n-alkanols (C sub(22)-C sub(32)) as indicators of land plant vegetation of different biosynthetic types were correlated with concentrations and distributions of pollen taxa in sediments of the same time horizons. Selected single pollen type data reveal details of vegetation changes, but the overall picture is best illustrated by summing pollen known to predominantly derive from C sub(4) plants or C sub(4) plus CAM plants. The C sub(4) plant signals in the biomarkers are recorded in the [delta] super(13)C data and in the abundances of C sub(31) and C sub(33) n-alkanes, and the C sub(32) n-alkanol. Calculated clusters of wind trajectories for austral summer and winter situations for the Holocene and the Last Glacial Maximum afford information on the source areas for the lipids and pollen and their transport pathways to the ocean. This multidisciplinary approach provides clear evidence of latitudinal differences in leaf wax lipid and pollen composition, with the Holocene sedimentary data paralleling the current major phytogeographic zonations. The northern sites (Congo Fan area and northern Angola Basin) get most of their terrestrial material from the Congo Basin and the Angolan highlands dominated by C sub(3) plants. Airborne particulates derived from the western and central South African hinterland dominated by deserts, semideserts, and savannah regions are rich in organic matter from C sub(4) plants. As can be expected from the present and glacial positions of the phytogeographic zones, the carbon isotopic signatures of n-alkanes and n-alkanols both become isotopically more enriched in super(13)C from north to south. In the northern part of the transect the relative importance of C sub(4) plant indicators is higher during the glacials than in the interglacials, indicating a northward extension of arid zones favoring grass vegetation. In the south, where grass-rich vegetation merges into semidesert and desert, the difference in C sub(4) plant indicators is small.