Cocco1ithophores as Indicators of Ocean Water Masses
123
Sediment Samples
The sediment samples used in this study were
recovered on the course of several cruises to
the eastern South Atlantic (Fig. 3). All surface
sediments were obtained with either box corers or
multi-corers. Thirty-eight surface sediment samples
ofthe eastern South Atlantic between 19° and 32°
S were investigated. Samples mostly originated
from the top of the Walvis Ridge as well as from
the continental margin off Southwest Africa (Fig.
3).
To obtain late Quaternary records from the
equatorial and eastern South Atlantic, two sediment
cores with well-established stratigraphies were
investigated (Fig. 3). Core GeoB 1117-2 W48.9'S
14°53.8'W, water depth 3984m) is from the MidAtlantic-Ridge in the northeasternmost Brasil
Basin, whereas core GeoB 1028-5 (20 0 06.2'S
09° 11.1 'E, water depth 2209m) comes from the
northern crest ofthe Walvis Ridge. The age models for the cores are based on a graphic correlation of the 8 18 0 records to the SPECMAP standard record (Imbrie et al. 1984). Isotope data are
presented elsewhere (Bickert and Wefer 1996;
Schneider et al. 1996).
A combined dilution/filtering technique as
described by Andruleit (1996) was used for the
preparation of sediment samples. A small amount
of sediment was weighed and brought into suspension. After treatment with a rotary splitter the suspension was filtered through polycarbonate membrane filters (Schleicher & Schuell™, 50mm diameter, O.4~m pore size). A monolayer of all sediment
particles was produced and subject to SEM analysis. All coccoliths were recorded in numbers per
gram dry sediment.
Results
The following chapter mainly contains new and, in
part, preliminary results. Additionally, somepreviously published data which are important in the
following discussion will also be reported briefly.
The results are presented separately for both investigated regions and the presented information
is limited to those species having a geological
record.
Equatorial Atlantic
Plankton
The spatial distribution patterns of coccolithophore
communities in the surface-waters show considerable variation in cell numbers. Maximum values
along the M29-3 transect of cell densities up to 300
X 10 3 coccospheres/l were found at 20 0 S, at the
equator, at 10-15°N, and at 200N (Fig. 4). In
between, coccolithophore standing crops are less
than lOx 10 3 cells/I. Emiliania huxleyi is the main
species causing the variations in cell concentrations
with the exception of the maximum off West~
Africa at about looN where Gephyrocapsa
oceanica is dominant.
Samples from the oligotrophic subtropical
gyre usually show low concentrations of coccolithophores (always <50 x 10 3 coccospheres/l) but
increased relative abundances of Umbellosphaera
irregularis and U. tenuis (Fig. 4). Other species
consistently recorded in the samples are
Calcidiscus leptoporus, and Syracosphaera spp.
Together they generally form less than 10% ofthe
flora and never exceed 20% in most samples.
Only few depth transect (0-200m of water
depth) have been investigated so far. The highest
values were always recorded in the top 20m ofthe
water column and, in addition, the data generally
confirm the findings made in the surface-water
transects. Therefore, these data will not be presented here.
Sediments
The development of the coccolithophore assemblages was investigated in a deep-sea sediment
core (GeoB 1117-2) for the past 300.000 years
(Fig. 5). Coccolith numbers vary from about
2.5xl0 9 up to almost 80xlO 9 coccoliths/g sediment,
and accumulation rates vary from 60x 1 0 9 up to
1500x10 9 coccoliths/m 2 /a. The highest numbers
associated with the highest accumulation rates
occur in isotope stage 2, 3, and in stage 7. The lowest values are indicative for the Holocene as well
as oxygen isotope stages 5 and 6. Gephyrocapsa
species (G. ericsonii and G. oceanica) dominate
123
Sediment Samples
The sediment samples used in this study were
recovered on the course of several cruises to
the eastern South Atlantic (Fig. 3). All surface
sediments were obtained with either box corers or
multi-corers. Thirty-eight surface sediment samples
ofthe eastern South Atlantic between 19° and 32°
S were investigated. Samples mostly originated
from the top of the Walvis Ridge as well as from
the continental margin off Southwest Africa (Fig.
3).
To obtain late Quaternary records from the
equatorial and eastern South Atlantic, two sediment
cores with well-established stratigraphies were
investigated (Fig. 3). Core GeoB 1117-2 W48.9'S
14°53.8'W, water depth 3984m) is from the MidAtlantic-Ridge in the northeasternmost Brasil
Basin, whereas core GeoB 1028-5 (20 0 06.2'S
09° 11.1 'E, water depth 2209m) comes from the
northern crest ofthe Walvis Ridge. The age models for the cores are based on a graphic correlation of the 8 18 0 records to the SPECMAP standard record (Imbrie et al. 1984). Isotope data are
presented elsewhere (Bickert and Wefer 1996;
Schneider et al. 1996).
A combined dilution/filtering technique as
described by Andruleit (1996) was used for the
preparation of sediment samples. A small amount
of sediment was weighed and brought into suspension. After treatment with a rotary splitter the suspension was filtered through polycarbonate membrane filters (Schleicher & Schuell™, 50mm diameter, O.4~m pore size). A monolayer of all sediment
particles was produced and subject to SEM analysis. All coccoliths were recorded in numbers per
gram dry sediment.
Results
The following chapter mainly contains new and, in
part, preliminary results. Additionally, somepreviously published data which are important in the
following discussion will also be reported briefly.
The results are presented separately for both investigated regions and the presented information
is limited to those species having a geological
record.
Equatorial Atlantic
Plankton
The spatial distribution patterns of coccolithophore
communities in the surface-waters show considerable variation in cell numbers. Maximum values
along the M29-3 transect of cell densities up to 300
X 10 3 coccospheres/l were found at 20 0 S, at the
equator, at 10-15°N, and at 200N (Fig. 4). In
between, coccolithophore standing crops are less
than lOx 10 3 cells/I. Emiliania huxleyi is the main
species causing the variations in cell concentrations
with the exception of the maximum off West~
Africa at about looN where Gephyrocapsa
oceanica is dominant.
Samples from the oligotrophic subtropical
gyre usually show low concentrations of coccolithophores (always <50 x 10 3 coccospheres/l) but
increased relative abundances of Umbellosphaera
irregularis and U. tenuis (Fig. 4). Other species
consistently recorded in the samples are
Calcidiscus leptoporus, and Syracosphaera spp.
Together they generally form less than 10% ofthe
flora and never exceed 20% in most samples.
Only few depth transect (0-200m of water
depth) have been investigated so far. The highest
values were always recorded in the top 20m ofthe
water column and, in addition, the data generally
confirm the findings made in the surface-water
transects. Therefore, these data will not be presented here.
Sediments
The development of the coccolithophore assemblages was investigated in a deep-sea sediment
core (GeoB 1117-2) for the past 300.000 years
(Fig. 5). Coccolith numbers vary from about
2.5xl0 9 up to almost 80xlO 9 coccoliths/g sediment,
and accumulation rates vary from 60x 1 0 9 up to
1500x10 9 coccoliths/m 2 /a. The highest numbers
associated with the highest accumulation rates
occur in isotope stage 2, 3, and in stage 7. The lowest values are indicative for the Holocene as well
as oxygen isotope stages 5 and 6. Gephyrocapsa
species (G. ericsonii and G. oceanica) dominate