558
Wagner and Dupont
concerning the source, amount and composition of
terrestrial biomarkers in eolian dust were made in
advance (Prahl et al. 1989). They also noted the
importance of post-depositional diagenetic alteration of biomarker compounds leading to an enrichment of the terrigenous biomarker fraction. To take
care ofthis problem, Poynter and Eglinton (1991)
and Westerhausen et al. (1993) introduced a degradation index of OM (HPA-Index), which is
independent of the quality of organic carbon supplied from land or surface waters. Furthermore,
Westerhausen et al. (1993) presented a model to
distinguish eolian from river-borne OM in the
Eastern Equatorial Atlantic using different proportions of plant wax n-alkanes. Again, definition of
endmember values, in this case the average concentration of n-alkanes in atmospheric dust, is the
most problematic factor of this application.
Deposition of Terrigenous OM to the
Modem and Late Quaternary Equatorial
Ocean
For the general discussion of terrestrial OM in
marine environments the modern and late Quaternary Equatorial Atlantic may serve as an interesting study area. Its model character is related to the
pronounced asymmetry between the western and
central-eastern Equatorial Atlantic with regard to
sourCe areas, mechanisms and distances of transport, and flux rates ofterrigenous OM.
The western Equatorial Atlantic is controlled by
the discharge ofterrigenous OM through the Amazon river (Showers and Angle 1986). Most of this
OM originates from the Amazon rain forest and is
rapidly buried in the Amazon Fan in
corresponcence to glacial/interglacial low- and
highstands ofthe sea level (Schneider et al. 1997;
SchlUnz et al. in press). New evidence from late
Quaternary sediments ofthe Ceara Rise, however,
reveals that terrigenous OM from the Amazon system at least temporarily escapes the Brasilian continental slope and is transported to more open settings (Rlihlemann et al. 1996). Estimates based on
isotopic data from this area suggest that 15-40%
ofthe total OM is ofterrigenous origin. Some part
of river-borne OM is likely advected even further
basinward than the Ceara Rise, where it is buried
in deeper basins ofthe low latitude North Atlantic
(Wagner subm).
Supply and distribution of terrigenous OM to the
central and eastern Equatorial Atlantic, in contrast,
is controlled by long-range eolian dust transport
from Africa (e.g. Hooghiemstra et al. 1986; Dupont
and Agwu 1991; Verardo and Ruddiman 1996;
Wagner 1998). Mixing of wind-blown with riverborne terrestrial OM occurs offshore the main
African rivers (Westerhausen et al. 1993; Dupont
this volume). This depositional pattern may principally have persisted over the last few millon years.
Numerous paleoenvironmental studies from the
Equatorial Atlantic and the adjacent continents, nevertheless, reveal intense fluctuations of eolian supply, river discharge and continental precipitation
related to past glacial-interglacial climatic and oceanographic changes.
Tracing Terrigenous OM in the Modern
Equatorial Atlantic
Eolian supply of terrigenous organic carbon to
pelagic, remote areas of the low latitude North
Atlantic is documented by organic geochemical
studies performed on atmospheric aerosols
(Simoneit 1977; Chesseletetal. 1981). Isotopic data
suggest that more than 80% of particulate organic
carbon in aerosols collected from the Sargasso Sea
is land-derived. This aspect may also be of relevance for the Equatorial Atlantic since the coupling of eolian supply and marine sedimentation has
been documented for many Quaternary records off
NW-Africa(TiedemannetaI.1989, 1994; Steinet
al. 1989; Hooghiemstra 1989; Dupont and Beug
1991), as well as the central (Pokras and Mix 1985;
DeMenocal et al. 1993; Ruddiman 1997; Wagner
subm) and eastern Equatorial Atlantic (Dupont and
Agwu 1992; Fredoux 1994; Wagner 1999).
Transfer of terrigenous OM to the deep-sea
ocean is evident from terrestrial biomarkers,
such as n-alkanes (Simoneit 1977; Wakeham and
Canuel 1988), stable isotopes (Crisp et al. 1979),
lignite oxidation products (Hamilton and Hedges
1988), and elevated CIN elemental ratios (Wefer
and Fischer 1993), which are reported of sediment
trap material from various oceanic settings. An enhanced eolian supply of terrigenous OM to the
Wagner and Dupont
concerning the source, amount and composition of
terrestrial biomarkers in eolian dust were made in
advance (Prahl et al. 1989). They also noted the
importance of post-depositional diagenetic alteration of biomarker compounds leading to an enrichment of the terrigenous biomarker fraction. To take
care ofthis problem, Poynter and Eglinton (1991)
and Westerhausen et al. (1993) introduced a degradation index of OM (HPA-Index), which is
independent of the quality of organic carbon supplied from land or surface waters. Furthermore,
Westerhausen et al. (1993) presented a model to
distinguish eolian from river-borne OM in the
Eastern Equatorial Atlantic using different proportions of plant wax n-alkanes. Again, definition of
endmember values, in this case the average concentration of n-alkanes in atmospheric dust, is the
most problematic factor of this application.
Deposition of Terrigenous OM to the
Modem and Late Quaternary Equatorial
Ocean
For the general discussion of terrestrial OM in
marine environments the modern and late Quaternary Equatorial Atlantic may serve as an interesting study area. Its model character is related to the
pronounced asymmetry between the western and
central-eastern Equatorial Atlantic with regard to
sourCe areas, mechanisms and distances of transport, and flux rates ofterrigenous OM.
The western Equatorial Atlantic is controlled by
the discharge ofterrigenous OM through the Amazon river (Showers and Angle 1986). Most of this
OM originates from the Amazon rain forest and is
rapidly buried in the Amazon Fan in
corresponcence to glacial/interglacial low- and
highstands ofthe sea level (Schneider et al. 1997;
SchlUnz et al. in press). New evidence from late
Quaternary sediments ofthe Ceara Rise, however,
reveals that terrigenous OM from the Amazon system at least temporarily escapes the Brasilian continental slope and is transported to more open settings (Rlihlemann et al. 1996). Estimates based on
isotopic data from this area suggest that 15-40%
ofthe total OM is ofterrigenous origin. Some part
of river-borne OM is likely advected even further
basinward than the Ceara Rise, where it is buried
in deeper basins ofthe low latitude North Atlantic
(Wagner subm).
Supply and distribution of terrigenous OM to the
central and eastern Equatorial Atlantic, in contrast,
is controlled by long-range eolian dust transport
from Africa (e.g. Hooghiemstra et al. 1986; Dupont
and Agwu 1991; Verardo and Ruddiman 1996;
Wagner 1998). Mixing of wind-blown with riverborne terrestrial OM occurs offshore the main
African rivers (Westerhausen et al. 1993; Dupont
this volume). This depositional pattern may principally have persisted over the last few millon years.
Numerous paleoenvironmental studies from the
Equatorial Atlantic and the adjacent continents, nevertheless, reveal intense fluctuations of eolian supply, river discharge and continental precipitation
related to past glacial-interglacial climatic and oceanographic changes.
Tracing Terrigenous OM in the Modern
Equatorial Atlantic
Eolian supply of terrigenous organic carbon to
pelagic, remote areas of the low latitude North
Atlantic is documented by organic geochemical
studies performed on atmospheric aerosols
(Simoneit 1977; Chesseletetal. 1981). Isotopic data
suggest that more than 80% of particulate organic
carbon in aerosols collected from the Sargasso Sea
is land-derived. This aspect may also be of relevance for the Equatorial Atlantic since the coupling of eolian supply and marine sedimentation has
been documented for many Quaternary records off
NW-Africa(TiedemannetaI.1989, 1994; Steinet
al. 1989; Hooghiemstra 1989; Dupont and Beug
1991), as well as the central (Pokras and Mix 1985;
DeMenocal et al. 1993; Ruddiman 1997; Wagner
subm) and eastern Equatorial Atlantic (Dupont and
Agwu 1992; Fredoux 1994; Wagner 1999).
Transfer of terrigenous OM to the deep-sea
ocean is evident from terrestrial biomarkers,
such as n-alkanes (Simoneit 1977; Wakeham and
Canuel 1988), stable isotopes (Crisp et al. 1979),
lignite oxidation products (Hamilton and Hedges
1988), and elevated CIN elemental ratios (Wefer
and Fischer 1993), which are reported of sediment
trap material from various oceanic settings. An enhanced eolian supply of terrigenous OM to the