A north to south transect of Holocene southeast Atlantic continental margin sediments: Relationship between aerosol transport and compound‐specific δ¹³C land plant biomarker and pollen records

Abstract

We examined near‐surface, late Holocene deep‐sea sediments at nine sites on a north‐south transect from the Congo Fan (4°S) to the Cape Basin (30°S) along the Southwest African continental margin. Contents, distribution patterns and molecular stable carbon isotope signatures of long‐chain n‐alkanes (C27‐C33) and n‐alkanols (C22‐C32) are indicators of land plant vegetation of different biosynthetic types, which can be correlated with concentrations and distributions of pollen taxa in the same sediments. Calculated clusters of wind trajectories and satellite Aerosol Index imagery afford information on the source areas for the lipids and pollen on land and their transport pathways to the ocean sites. This multidisciplinary approach on an almost continental scale provides clear evidence of latitudinal differences in lipid and pollen composition paralleling the major phytogeographic zonations on the adjacent continent. Dust and smoke aerosols are mainly derived from the western and central South African hinterland dominated by deserts, semi‐deserts and savannah regions rich in C4 and CAM plants. The northern sites (Congo Fan area and northern Angola Basin), which get most of their terrestrial material from the Congo Basin and the Angolan highlands, may also receive some material from the Chad region. Very little aerosol from the African continent is transported to the most southerly sites in the Cape Basin. As can be expected from the present position of the phytogeographic zones, the carbon isotopic signatures of the n‐alkanes and n‐alkanols both become isotopically more enriched in 13C from north to south. The results of the study suggest that this combination of pollen data and compound‐specific isotope geochemical proxies can be effectively applied in the reconstruction of past continental phytogeographic developments.

Terrigenous plant wax inputs to the Arabian Sea: Implications for the reconstruction of winds associated with the Indian Monsoon

“…These compounds are periodically ablated from living plants by wind (Hadley and Smith, 1989) and can therefore be analyzed in sediments as a means of reconstructing eolian input to the marine environment (e.g. Ohkouchi et al, 1997;Huang et al, 2000;Rommerskirchen et al, 2003). Plant waxes in marine sediments on coastal margins can also be fluvially derived (e.g.…”

“…Eolian-derived plant waxes have the potential to be direct proxies for both wind strength and trajectory (e.g. Ohkouchi et al, 1997;Huang et al, 2000;Rommerskirchen et al, 2003;Schefuß et al, 2003). Sedimentary plant wax records may also reflect changes in the source area of the compounds through time.…”

Tropical limestone forest resilience and late Pleistocene foraging during MIS-2 in the Tràng An massif, Vietnam

“…Hadley 1980;Koch & Ensikat 2008;Kosma et al 2009). The longer the n-alkane chain length the more energy and resources are required for creation, but the greater the protection provided (Rommerskirchen et al 2003). Within equatorial regions where insolation is high plants produce the long n-alkane chains, provided there is also sufficient moisture.…”

“…While precipitation arrives with marked monsoon seasonality and is often poorly retained for plant-life at sub-tropical latitudes, compared to their southern lowland rainforest counterparts (Chang et al, 2005) summer insolation levels are routinely more intense than those experienced closer to the Equator (Paillard et al 1996;Wang & Enfield 2001). This combination has a profound effect on the production of plant n-alkanes and n-alkanoic acids that can be tracked and through them past environmental conditions can be reconstructed (Rommerskirchen et al 2003).…”

Lipid biomarkers in Lake Enol (Asturias, Northern Spain): Coupled natural and human induced environmental history

“…, with í = 13, n = 33], is a good proxy for distinguishing between the predominance of low vS. high MW n-alkanes (Pancost et al, 2002;Rommerskirschen et al, 2003). The carbon preference index (CPI; Bray and Evans, 1961), calcu-…”