Terrestrial Organic Matter in Marine Sediments
565
nate from a wide range of vegetation zones such
as rain forest, savannah, desert, etc. Hence, total
pollen counts are not sufficiently specific to detect
eolian transport from the arid savannah-covered
aeras. Grass pollen, in contrast, are indicative for
these potential C4-grass habitats. Both, total and
grass pollen, show elevated contents within the
approximate limit ofthe winter dust plume documenting eolian admixture of grass plant material to
these marine settings. Hence, it might be expected
that this organic fraction has an effect on the bulk
sedimentary 8 13 C org signal. We therefore compared
quantitative estimates based on isotopic and organic
petrologic analyses and calculated the amount of
C4-material which equilibrates the difference.
TIlese maximum estimates were grouped into three
intervals «I 0%, 10-15%,> 15%) and are displayed
as triangles in figures lOa-b. Highest proportions
ofC4-debris match fairly well within the southern
limits of the dust plume and the area of enhanced
grass pollen. Lower C4-proportions were calculated for external or distal parts ofthe dust plume
limit. Intermediate proportions observed at about
I OOW and 5 0 S cannot be explained at the moment
since there are no palynological data available for
comparision. It should be noted here that pollen and
spore fluxes are extremely low in this area. With
regard to the discussion on charcoal deposition
(Verardo and Ruddiman 1996; see cross signature
in Fig. lOb for position) our results do neither support nor disprove this assumption, since modern
supply of "charcoal" was estimated to be zero.
The Past Glacial/Interglacial Equatorial
Atlantic
TIle new evidence of enhanced deposition of windblown "charcoal" to the central Equatorial Atlantic
(Verardo and Ruddiman 1996) has fueled the discussion on the importance of terrigenous organic
carbon supply to open ocean areas, especially during glacial periods. Past glacial/interglacial fluctuations in supply and accumulation of terrigenous OM
in the Equatorial Atlantic are deduced from cyclic
variations in palynomorphs (e.g. Hooghiemstra and
Agwu 1988; Fredoux 1994; Dupont et al. 1998;
Dupont this volume), fresh water diatoms and
phytoliths from grass cuticules (e.g. DeMenocal et
al. 1993), terrigenous macerals (Stein et al. 1989;
Wagner 1998, 1999; Wagner subm), "charcoal"
(Verardo and Ruddiman 1996), and higher plant
lipids (e.g. Poynter et al. 1989). All these different
records correlate to bulk terrigenous dust fluxes
giving evidence of strong glacial!interglacial
changes in atmospheric circulation intensity.
Tn the following discussion we transfer our results from the modern ocean into the geological
past. Our study is focused on one single glacial!
interglacial cycle from the center (ODP Site 663)
and from the north (core 776) of the Equatorial Divergence (Fig. Sa). Isotopic stages 11 and 12 (390480 ky) were chosen for this case study because
bulk parameters of Site 663 clearly reveal strong
glaciallinterglacial contrasts in carbonate, sand,
biogenous opal and terrigenous dust (Fig. 11;
DeMenocal et al. 1993). Since similar patterns
have been observed in many other Late Quaternary records of the South Atlantic (DeMenocal et
al. 1993; Verardo and McIntyre 1994; Bickert and
Wefer 1996; Ruddiman 1997) we consider the interval studied to be typical at least for this sector
ofthe Equatorial Atlantic.
Figure II shows sedimentological parameters
of isotopic stages II and 12 at OPD Site 663. Accumulation rates of terrigenous matter reveal high
amplitude variations during glacial stage 12 which,
in general, are paralleled by enhanced opal and
organic carbon. Interglacial stage 11, in contrast,
is characterized by persistent low levels of all three
parameters. The correspondence of these records
documents the coupling of wind-induced
paleoproductivity and enhanced eolian supply during glacial stages. Carbonate and sand records, on
the other hand, show opposite trends compared to
TOC and biogenous opal. Their pattern is attributed to glacially increased carbonate dissolution
due to OM remineralization or, even more important, by the lateral inflow of corrosive bottom waters from the Antarctic Ocean (e.g. Verardo and
McIntyre 1994, Bickert and Wefer 1996).
Results from our organic geochemical analyses
and the flux record of phytoliths of Site 663 are illustrated in Fig. 12. Correlation ofTOC and HI indicate glacially enhanced marine organic carbon
accumulation below the center of the Equatorial
Divergence, although fluctuations in paleo-
565
nate from a wide range of vegetation zones such
as rain forest, savannah, desert, etc. Hence, total
pollen counts are not sufficiently specific to detect
eolian transport from the arid savannah-covered
aeras. Grass pollen, in contrast, are indicative for
these potential C4-grass habitats. Both, total and
grass pollen, show elevated contents within the
approximate limit ofthe winter dust plume documenting eolian admixture of grass plant material to
these marine settings. Hence, it might be expected
that this organic fraction has an effect on the bulk
sedimentary 8 13 C org signal. We therefore compared
quantitative estimates based on isotopic and organic
petrologic analyses and calculated the amount of
C4-material which equilibrates the difference.
TIlese maximum estimates were grouped into three
intervals «I 0%, 10-15%,> 15%) and are displayed
as triangles in figures lOa-b. Highest proportions
ofC4-debris match fairly well within the southern
limits of the dust plume and the area of enhanced
grass pollen. Lower C4-proportions were calculated for external or distal parts ofthe dust plume
limit. Intermediate proportions observed at about
I OOW and 5 0 S cannot be explained at the moment
since there are no palynological data available for
comparision. It should be noted here that pollen and
spore fluxes are extremely low in this area. With
regard to the discussion on charcoal deposition
(Verardo and Ruddiman 1996; see cross signature
in Fig. lOb for position) our results do neither support nor disprove this assumption, since modern
supply of "charcoal" was estimated to be zero.
The Past Glacial/Interglacial Equatorial
Atlantic
TIle new evidence of enhanced deposition of windblown "charcoal" to the central Equatorial Atlantic
(Verardo and Ruddiman 1996) has fueled the discussion on the importance of terrigenous organic
carbon supply to open ocean areas, especially during glacial periods. Past glacial/interglacial fluctuations in supply and accumulation of terrigenous OM
in the Equatorial Atlantic are deduced from cyclic
variations in palynomorphs (e.g. Hooghiemstra and
Agwu 1988; Fredoux 1994; Dupont et al. 1998;
Dupont this volume), fresh water diatoms and
phytoliths from grass cuticules (e.g. DeMenocal et
al. 1993), terrigenous macerals (Stein et al. 1989;
Wagner 1998, 1999; Wagner subm), "charcoal"
(Verardo and Ruddiman 1996), and higher plant
lipids (e.g. Poynter et al. 1989). All these different
records correlate to bulk terrigenous dust fluxes
giving evidence of strong glacial!interglacial
changes in atmospheric circulation intensity.
Tn the following discussion we transfer our results from the modern ocean into the geological
past. Our study is focused on one single glacial!
interglacial cycle from the center (ODP Site 663)
and from the north (core 776) of the Equatorial Divergence (Fig. Sa). Isotopic stages 11 and 12 (390480 ky) were chosen for this case study because
bulk parameters of Site 663 clearly reveal strong
glaciallinterglacial contrasts in carbonate, sand,
biogenous opal and terrigenous dust (Fig. 11;
DeMenocal et al. 1993). Since similar patterns
have been observed in many other Late Quaternary records of the South Atlantic (DeMenocal et
al. 1993; Verardo and McIntyre 1994; Bickert and
Wefer 1996; Ruddiman 1997) we consider the interval studied to be typical at least for this sector
ofthe Equatorial Atlantic.
Figure II shows sedimentological parameters
of isotopic stages II and 12 at OPD Site 663. Accumulation rates of terrigenous matter reveal high
amplitude variations during glacial stage 12 which,
in general, are paralleled by enhanced opal and
organic carbon. Interglacial stage 11, in contrast,
is characterized by persistent low levels of all three
parameters. The correspondence of these records
documents the coupling of wind-induced
paleoproductivity and enhanced eolian supply during glacial stages. Carbonate and sand records, on
the other hand, show opposite trends compared to
TOC and biogenous opal. Their pattern is attributed to glacially increased carbonate dissolution
due to OM remineralization or, even more important, by the lateral inflow of corrosive bottom waters from the Antarctic Ocean (e.g. Verardo and
McIntyre 1994, Bickert and Wefer 1996).
Results from our organic geochemical analyses
and the flux record of phytoliths of Site 663 are illustrated in Fig. 12. Correlation ofTOC and HI indicate glacially enhanced marine organic carbon
accumulation below the center of the Equatorial
Divergence, although fluctuations in paleo-