Kaolinite and Chlorite as Tracers of Modem and Late Quaternary Deep Water Circulation
293
related stratification of the opposite water masses.
A good example is the ACC region around the
Greenwich Meridian between 40° Sand SO° S
where NADW is injected into the ACC (Fig. 3).
Highest kaolinite/chlorite-ratio occur in surface
sediments that are bathed by NADW at intennediate water depths. In both shallower and deeper
water depths, surface sediments which are bathed
by upper or lower CPDW exhibit lower kaolinite/
chlorite-ratios.
The kaolinite/chlorite-ratio is not a relevant tracers of deep water advection south of the ACC/
Weddell Gyre boundary. The kaolinite/chlorite-ratio in surface sediments underneath the Weddell
Gyre is higher than in the ACC region (Fig. 2, 3)
due to increased kaolinite fluxes within water
masses ofthe Weddell Gyre. This kaolinite originates from fossil kaolinite-bearing sedimentary
rocks of East Antarctica (Ehrmann et al. 1992;
Petschick et al. 1996). However, no clay mineral
exchange beween the current systems ofthe ACC
and Weddell Gyre takes place as evidenced by
marked differences in illite chemistry in the respective underlying sediments (Petschick et al. 1996;
Diekmann et al. 1996).
Late Quaternary Deep Water Advection
Inferred from the Kaolinite/Chlorite-Ratio
Diekmann et al. (1996) discussed down core variations of clay mineral distributions in 19 sediment
cores on a transect across the eastern South
Atlantic and the adjoining part of the Southern
Ocean from the Walvis Ridge to the eastern
Weddell Abyssal Plain. They underlined the paleoceanographic significance ofthe kaolinite/chloriteratio as a reliable tracer of deep water advection
in that area. We will now focus on new results from
neighbouring areas and interpret them in the context of fluxes of terrigenous matter that support the
prominent role of current transport on sedimentation.
Temporal Variations of Terrigenous
Sediment Accumulation
The relative amount of terrigenous matter in marine sediments depends on the influx ofterrigenous
matter in relation to biological export production,
preservation of biogenic particles, and mutual dilution effects. Relative proportions of terrigenous
matter do not exeed 2S% in the sediment cores from
the southeast Atlantic sector of the Southern Ocean
(PS2082-1, PSI768-8) and westernmost Indian
sector of the Southern Ocean (PS2S64-3). Sediment cores PS249S-3, PS2498-1, and PS2499-S,
recovered from the Mid-Atlantic Ridge in the central to northern ACC region, contain between 20
and 70% terrigenous matter, with highest values in
sediment core intervals representing glacial stages.
In the western part of the study area, proportions
of terrigenous matter also vary markedly in sediment core GeoB 2110-4 from the Vema Channel
region (30-90%) and sediment core PS 1786-1 from
the South Sandwich Trench (40-60%), again with
peak values in glacial core intervals.
To deduce the quantitative signifcance ofterrigenous particle deposition in space and time we have
calculated accumulation rates ofterrigenous matter (AR'err-values) (Fig. 4). Highest AR,errvalues occur in GeoB211 0-4 (2-10 g cm' z ka· t )
from the Vema Channel region and PS2498-1 and
PS2499-S (2-11 g cm,zka· t ) from the Mid-Atlantic
Ridge. Moderate AR",,-values are evident in
PS249S-3 (0.S-2.0 g cm' z ka· t ) from the MidAtlantic Ridgeand PS 1768-8 (0.S-2.S g cm,zka· t )
from the western SW Indian Ridge. Lowest
AR -values were estimated for PS2082-1
terr
(0.2-1.S g cm' Z ka· t ) from the Agulhas Basin and
PS2S64-3 (0.2-l.S g cm' z ka· t ) from the eastern
SW Indian Ridge.
High ARterr-values in GeoB21 10-4 document
the core position close to the South American continental margin where, especially in the Vema Channel region, a strong terrigenous sediment influx from
the continent takes place. All other investigated
sediment cores were recovered within the reaches
of the ACC and exhibit inconsistent Arterr-values
without any distinct spatial or water depth-related
contrasts.
At all core sites AR,,,,-valueswere higher during glacial periods compared to interglacials. In
detail, patterns of glacial-interglacial ARte,,-values
variations exhibit marked differences between and
within each sediment core. In all investigated sediment cores highest AR"rr -values appear during isotope stage 2 (Fig. 4) that are increased by several
293
related stratification of the opposite water masses.
A good example is the ACC region around the
Greenwich Meridian between 40° Sand SO° S
where NADW is injected into the ACC (Fig. 3).
Highest kaolinite/chlorite-ratio occur in surface
sediments that are bathed by NADW at intennediate water depths. In both shallower and deeper
water depths, surface sediments which are bathed
by upper or lower CPDW exhibit lower kaolinite/
chlorite-ratios.
The kaolinite/chlorite-ratio is not a relevant tracers of deep water advection south of the ACC/
Weddell Gyre boundary. The kaolinite/chlorite-ratio in surface sediments underneath the Weddell
Gyre is higher than in the ACC region (Fig. 2, 3)
due to increased kaolinite fluxes within water
masses ofthe Weddell Gyre. This kaolinite originates from fossil kaolinite-bearing sedimentary
rocks of East Antarctica (Ehrmann et al. 1992;
Petschick et al. 1996). However, no clay mineral
exchange beween the current systems ofthe ACC
and Weddell Gyre takes place as evidenced by
marked differences in illite chemistry in the respective underlying sediments (Petschick et al. 1996;
Diekmann et al. 1996).
Late Quaternary Deep Water Advection
Inferred from the Kaolinite/Chlorite-Ratio
Diekmann et al. (1996) discussed down core variations of clay mineral distributions in 19 sediment
cores on a transect across the eastern South
Atlantic and the adjoining part of the Southern
Ocean from the Walvis Ridge to the eastern
Weddell Abyssal Plain. They underlined the paleoceanographic significance ofthe kaolinite/chloriteratio as a reliable tracer of deep water advection
in that area. We will now focus on new results from
neighbouring areas and interpret them in the context of fluxes of terrigenous matter that support the
prominent role of current transport on sedimentation.
Temporal Variations of Terrigenous
Sediment Accumulation
The relative amount of terrigenous matter in marine sediments depends on the influx ofterrigenous
matter in relation to biological export production,
preservation of biogenic particles, and mutual dilution effects. Relative proportions of terrigenous
matter do not exeed 2S% in the sediment cores from
the southeast Atlantic sector of the Southern Ocean
(PS2082-1, PSI768-8) and westernmost Indian
sector of the Southern Ocean (PS2S64-3). Sediment cores PS249S-3, PS2498-1, and PS2499-S,
recovered from the Mid-Atlantic Ridge in the central to northern ACC region, contain between 20
and 70% terrigenous matter, with highest values in
sediment core intervals representing glacial stages.
In the western part of the study area, proportions
of terrigenous matter also vary markedly in sediment core GeoB 2110-4 from the Vema Channel
region (30-90%) and sediment core PS 1786-1 from
the South Sandwich Trench (40-60%), again with
peak values in glacial core intervals.
To deduce the quantitative signifcance ofterrigenous particle deposition in space and time we have
calculated accumulation rates ofterrigenous matter (AR'err-values) (Fig. 4). Highest AR,errvalues occur in GeoB211 0-4 (2-10 g cm' z ka· t )
from the Vema Channel region and PS2498-1 and
PS2499-S (2-11 g cm,zka· t ) from the Mid-Atlantic
Ridge. Moderate AR",,-values are evident in
PS249S-3 (0.S-2.0 g cm' z ka· t ) from the MidAtlantic Ridgeand PS 1768-8 (0.S-2.S g cm,zka· t )
from the western SW Indian Ridge. Lowest
AR -values were estimated for PS2082-1
terr
(0.2-1.S g cm' Z ka· t ) from the Agulhas Basin and
PS2S64-3 (0.2-l.S g cm' z ka· t ) from the eastern
SW Indian Ridge.
High ARterr-values in GeoB21 10-4 document
the core position close to the South American continental margin where, especially in the Vema Channel region, a strong terrigenous sediment influx from
the continent takes place. All other investigated
sediment cores were recovered within the reaches
of the ACC and exhibit inconsistent Arterr-values
without any distinct spatial or water depth-related
contrasts.
At all core sites AR,,,,-valueswere higher during glacial periods compared to interglacials. In
detail, patterns of glacial-interglacial ARte,,-values
variations exhibit marked differences between and
within each sediment core. In all investigated sediment cores highest AR"rr -values appear during isotope stage 2 (Fig. 4) that are increased by several