Multiproxy Studies

I cooperated in a number of studies that compare different proxies to test new ones and to use complementary methods aiming at more detailed palaeoenvironmental reconstructions.

Composition, age, and provenance of organic matter in NW African dust over the Atlantic Ocean
Eglinton, T.I., Eglinton, G., Dupont, L., Sholkovitz, E.R., Montluçon, D., Reddy, C.M.
Geochemistry, Geophysics, Geosystems 3 (2002)
doi: 10.1029/2001GC000269

Eolian dust deposited on a meteorology buoy over the boreal winter and spring of 1992/1993 in the Northeast Atlantic off Northwest Africa (18N, 22W) afforded sufficient material for detailed assessment of its biogeochemical characteristics and provenance. The sample was subjected to microscopic examination and bulk, elemental, isotopic, black carbon, and molecular (lignin, lipid) analyses. The bulk elemental composition and organic carbon (OC) content (1.02% dry weight) establishes the dust’s origin as continental upper crust and is typical of dusts that emanate fromWest Africa. These data are in accord with the extensive satellite imagery documenting the transit of dust clouds from the Sahara and Sahel regions (e.g., NASA TOMS aerosol index). Microscopic examination reveals that charcoal-like particles from vegetation fires (‘‘black carbon’’ (BC)) are the most abundant morphologically distinct organic components. Accelerator mass spectrometry (AMS) 14C analysis yields conventional 14C ages for bulk OC of 1260 ± 40 years and BC of 2070 ± 35 years.


Temporal variability of fluxes of eolian-transported freshwater diatoms, phytoliths, and pollen grains off Cape Blanc as reflection of land-atmosphere-ocean interactions in northwest Africa
Romero, O.E., Dupont, L.M., Wyputta, U., Jahns, S., Wefer, G.
Journal of Geophysical Research 108 C5 (2003) 3153-3164

Abstract
Fluxes of airborne freshwater diatoms (FD), phytoliths (PH), and pollen grains (PO) collected with sediment traps off Cape Blanc, northwest Africa, from 1988 till 1991 are presented. Both continental rainfall variations and wind mean strength and direction play a key role in the temporal fluctuations of the fluxes of eolian traces in the pelagic realm. Drier conditions in Northern Africa in 1987 could have preceded the high lithogenic input and moderate FD flux in 1988. The PH peak in summer 1988 was probably caused by increased wind velocity. Wetter rainy seasons of 1988/89 might have promoted a significant pollen production in summer 1989, and FD in late 1989 and early 1990, as well as contributed to the reduction of the lithogenic flux in 1989/90. Decreased fluxes of FD, PH and PO, and higher contribution of the 6–11 mm lithogenic fraction in 1991 would mainly reflect minor intensity and decreased amount of continental trade winds. Air-mass backward trajectories confirm that the Saharan Air Layer is predominantly involved in the spring/summer transport. Trade winds play a decisive role in the fall/winter months, but also contribute to the transport during late spring/summer. Origin of wind trajectories does not support a direct relationship between transporting wind-layers and material source areas in Northern Africa. High winter fluxes of eolian tracers and high amount of trade winds with continental origin in summer warn against a simplistic interpretation of the seasonal eolian signal preserved in the sediments off Cape Blanc, and the wind layer involved in its transport.

Complementary datasets of terrestrial biomarkers and pollen. While the isotopic composition of leaf-wax components of terrestrial origin indicates the ratio between C3 and C4 plants of the vegetation in the source area, the pollen record indicates the extension of different biomes.


Mapping of C4 plant input from North West Africa into North East Atlantic sediments
Huang, Y., Dupont. L., Sarnthein, M., Hayes, J.M., Eglinton, E.
Geochimica Cosmochimica Acta 64 (2000) 3505-3513

Mapping the abundance of 13C in leaf-wax components in surface sediments recovered from the seafloor off northwest Africa (0–35°N) compared with the distribution of pollen in the same sediments reveals a clear pattern of d13C distribution, indicating systematic changes in the proportions of terrestrial C3 and C4 plant input.


n-Alkane and pollen reconstruction of terrestrial climate and vegetation for N.W. Africa over the last 160 kyr
Zhao, M., Dupont, L., Eglinton, G., Teece, M.
Organic Geochemistry 34 (2003) 131-143

Proxy environmental records have been obtained for the last 160 kyr from the well-studied ODP Site 658, ca. 200 km West of Cap Blanc, N.W. Africa (20°05'N, 18°35'W; 2263 m water depth). This collective assessment of several terrigenous proxies (lithogenic fraction, n-alkane content and d13C values,and pollen counts) provides a better understanding of the climate and vegetation history of the N.W. African hinterland.


A North to South transect of Holocene Southeast Atlantic continental margin sediments: relationship between aerosol transport and compound-dpecific d13C land plant biomarker and pollen records
Rommerskirchen, F., Eglinton, G., Dupont, L., Günter, U., Wenzel, C., Rullkötter, J.
Geochemistry, Geophysics, Geosystems 4 (2003)
doi:10.1029/2003GC000541

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.


Glacial/Interglacial changes in Southern Africa: compound-specific d13C land plant biomarker and pollen records from Southeast Atlantic continental margin sediments
Rommerskirchen, F., Eglinton, G., Dupont, L., Rullkötter, J.
Geochemistry, Geophysics, Geosystems 7 (2006)
doi:10.1090/2005GC001223

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°S) to the Cape Basin (30°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 (C27-C33) and n-alkanols (C22-C32) 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.

We have been testing the biomarker taraxerol as a proxy for Mangroves and used both proxies to unravel the relation ship between the mangrove records and sea-level changes.


Taraxerol and Rhizophora pollen as proxies for tracking past Mangrove ecosystems
Versteegh, G.J.M., Schefuß. E., Dupont, L., Marret, F., Sinninghe Damsté, J., Jansen, F.
Geochimica et Cosmochimica Acta 68 (2004) 411-422

Abstract
Angola Basin and Cape Basin (southeast Atlantic) surface sediments and sediment cores show that maxima in the abundance of taraxerol (relative to other land-derived lipids) covary with maxima in the relative abundance of pollen from the mangrove tree genus Rhizophora and that in the surface sediments offshore maxima in the relative abundance of taraxerol occur at latitudes with abundant coastal mangrove forests. Together with the observation that Rhizophora mangle and Rhizophora racemosa leaves are extraordinarily rich in taraxerol, this strongly indicates that taraxerol can be used as a lipid biomarker for mangrove input to the SE Atlantic. The proxy-environment relations for taraxerol and Rhizophora pollen down-core show that increased taraxerol and Rhizophora pollen abundances occur during transgressions and periods with a humid climate. These environmental changes modify the coastal erosion and sedimentation patterns, enhancing the extent of the mangrove ecosystem and/or the transport of mangrove organic matter offshore.

Impacts of rapid sea-level rise on mangrove deposit erosion: application of taraxerol and Rhizophora records
Kim, j.-H., Dupont, L., Behling, H., Versteegh, G.J.M.
Journal of Quaternary Science 20 (2005) 221-225

Abstract
We investigated a well-dated marine sediment core from the tropical SE Atlantic covering the last 25 kyr, applying taraxerol and Rhizophora pollen as organic geochemical and palynological proxies for mangrove, respectively. Taraxerol records are positively correlated with Rhizophora pollen records, showing an enhanced supply of mangrove materials into deep-sea environments during the last deglaciation (Termination I). Sedimentation rates peaked during Meltwater Pulses 1A and 1B, which were associated with the maxima of taraxerol and Rhizophora pollen. This study supports the view that mangrove input was dominantly controlled by erosion of mangrove-rich shelf sediments during the transgressions. Whether reworked materials were penecontemporaneous or from much older deposits formed during previous sea-level cycles is discussed.

We compared pollen counts with the results of petrochemical characterisation of terrestrial organic matter in marine sediments.

 Wagner_et_al._2003.pdf

Wagner, T., Zabel, M., Dupont, L., Holvoeth, J., Schubert, C.J., 2003. Terrigenous signals in sediments of the low latitude Atlantic - implications to environmental variations during the late Quaternary: part I, organic carbon. In: Wefer, G., Mulitza, S., & Ratmeyer, V. (eds.). The South Atlantic in the Late Quaternary: Reconstruction of Material Budget and Current Systems. Springer, Berlin: 295-322.

 Wagner_Dupont_1999.pdf

Wagner, T., Dupont, L.M., 1999. Terrestrial OM in marine sediments: analytical approaches and eolian-marine records of the central Equatorial Atlantic. In. Fischer, G. & Wefer, G. (eds.). Proxies in Paleoceanography, examples from the South Atlantic. Springer, Berlin: 547-574. Abstract

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