The Distribution of Living Planktic Foraminifera in Relation to Southeast Atlantic Oceanography
93
Material and Methods
Plankton and water samples were collected during
METEOR cruises M6/6 ITom February 23 to March
21,1988, M16/1 from April 4 to 11, 1991, andM2~/
1 on February 10, 1993 (Table1). The station POSItions and surface currents are shown in Fig. 1. All
samples were collected during the same season,
austral autumn. A Multiple Opening-Closing Net
(multi-net) equipped with five 2-liter Niskin bottles
was used to obtain planktic foraminifera and seawater samples for faunal and oxygen isotope investigations of foraminifera and water. The Multiple
Opening-Closing Net has a 0.25 m 2 opening and five
nets of 64 I-lm mesh size. The depth intervals sampled were 0-25 m, 25-50 m, 50-100 m, 100-150 m,
and 150-300 m for the stations GeoB 1016 through
GeoB 1046 from cruise M6/6. During cruise M 16/
1 we towed the intervals 0-50 m, 50-100 m, 100300 m, 300-500 m, and 500-1000 m at stations GeoB
1402 through GeoB 1407, because we wanted to
collect deep-living Globorotaliid species.
The multi-net was vertically hauled at a speed
of 0.3 m/s. The samples were fixed with HgCl 2 and
stored at approximately 4° C. Seawater temperature, conductivity, pressure and dissolved oxygen
were measured at each station by using a CTD
profiler (Fig. 2).
The samples from stations GeoB 1016 through
GeoB 1046 were halved with the Honjo-rotary
splitter and rinsed with fresh water. The residue
was ashed at <150° C to remove the cytoplasm of
the foraminifera and other organic material. This
treatment precluded determination of a dead/live
ratio as well as the proportion ofGlobigerinoides
ruber pink because the red pigment was destroyed
in the roasting process. The samples from GeoB
1402 through GeoB 1407, however, were picked
from the wet solution. Specimens with protoplasm
were separated from those with empty shells before the organic matter was removed with a NaOel
solution to obtain dead/live and pink/white ratios.
These foraminifera shells were used for stable isotope analysis.
All specimens> 63 I-lm were counted and calculated as total individuals per m 3 • The total concentration of foraminifers per m 3 were calculated
by dividing the absolute number of foraminifers per
depth interval by the filtered water volume (assuming 100% efficiency filtering). Determination of the
concentration (individuals/m 3 ) of each species is
based on quantitative species analyses of aliquots
with at least 300 individuals from the residue >63
I-lm. The species were identified using the taxonomy
of Be (1977) and Hemleben et al. (1989). Because
an accurate identification of individuals <100 I-lm is
very difficult, we identified only specimens> 1 00 I-lm
(for samples of cruise M 6/6) and 128 I-lm (for samples of cruise M 16/1 and 23/1). The latter size class
was chosen because the size of the specimens of
these samples was precisely measured at 8 I-lm size
intervals with a scaled occular for stable oxygen
isotope analysis.
The vertical distribution of selected species has
been contoured using the software MS-DOS
SYSTAT, 1990, using a negatively, exponentially
weighted smoothing (McLain 1974). For the
regional distribution maps we used the program
SURFER 4.0 (Golden Software Inc. Colorado,
kridging analyses).
Stable oxygen isotope ratios of the planktic
foraminifera were measured with a Finnigan MAT
251 mass spectrometer. The isotope composition is
expressed in the standard 8-notation, where
8 = (Rsample - Rstandard)/Rstandard * 1000 (R:
"0/ 16 0) relative to the Pee Dee belemnite (PDB)
standard. Because most of the towed individuals
are smaller than 250 I-lm, tbin-walled, and less abundant than in sediment samples (see Table 2), it was
often difficult to get enough individuals for an isotope measurement. For this reason it was only p~ssible to carry out single measurements of species
and/or size classes. Depending on the species and
size, 3 (for example the large and thick-walled G.
menardii 500-600 I-lm) to 70 (like the small and
rather thin-walled speciesG. ruberw. 125-250 I-lm)
individuals were used for one measurement.
Results and Discussion
Standing Stock in the Equatorial and
Eastern South Atlantic
Plankton tows from the South Equatorial Current,
South Equatorial Counter Current, Angola Current,
93
Material and Methods
Plankton and water samples were collected during
METEOR cruises M6/6 ITom February 23 to March
21,1988, M16/1 from April 4 to 11, 1991, andM2~/
1 on February 10, 1993 (Table1). The station POSItions and surface currents are shown in Fig. 1. All
samples were collected during the same season,
austral autumn. A Multiple Opening-Closing Net
(multi-net) equipped with five 2-liter Niskin bottles
was used to obtain planktic foraminifera and seawater samples for faunal and oxygen isotope investigations of foraminifera and water. The Multiple
Opening-Closing Net has a 0.25 m 2 opening and five
nets of 64 I-lm mesh size. The depth intervals sampled were 0-25 m, 25-50 m, 50-100 m, 100-150 m,
and 150-300 m for the stations GeoB 1016 through
GeoB 1046 from cruise M6/6. During cruise M 16/
1 we towed the intervals 0-50 m, 50-100 m, 100300 m, 300-500 m, and 500-1000 m at stations GeoB
1402 through GeoB 1407, because we wanted to
collect deep-living Globorotaliid species.
The multi-net was vertically hauled at a speed
of 0.3 m/s. The samples were fixed with HgCl 2 and
stored at approximately 4° C. Seawater temperature, conductivity, pressure and dissolved oxygen
were measured at each station by using a CTD
profiler (Fig. 2).
The samples from stations GeoB 1016 through
GeoB 1046 were halved with the Honjo-rotary
splitter and rinsed with fresh water. The residue
was ashed at <150° C to remove the cytoplasm of
the foraminifera and other organic material. This
treatment precluded determination of a dead/live
ratio as well as the proportion ofGlobigerinoides
ruber pink because the red pigment was destroyed
in the roasting process. The samples from GeoB
1402 through GeoB 1407, however, were picked
from the wet solution. Specimens with protoplasm
were separated from those with empty shells before the organic matter was removed with a NaOel
solution to obtain dead/live and pink/white ratios.
These foraminifera shells were used for stable isotope analysis.
All specimens> 63 I-lm were counted and calculated as total individuals per m 3 • The total concentration of foraminifers per m 3 were calculated
by dividing the absolute number of foraminifers per
depth interval by the filtered water volume (assuming 100% efficiency filtering). Determination of the
concentration (individuals/m 3 ) of each species is
based on quantitative species analyses of aliquots
with at least 300 individuals from the residue >63
I-lm. The species were identified using the taxonomy
of Be (1977) and Hemleben et al. (1989). Because
an accurate identification of individuals <100 I-lm is
very difficult, we identified only specimens> 1 00 I-lm
(for samples of cruise M 6/6) and 128 I-lm (for samples of cruise M 16/1 and 23/1). The latter size class
was chosen because the size of the specimens of
these samples was precisely measured at 8 I-lm size
intervals with a scaled occular for stable oxygen
isotope analysis.
The vertical distribution of selected species has
been contoured using the software MS-DOS
SYSTAT, 1990, using a negatively, exponentially
weighted smoothing (McLain 1974). For the
regional distribution maps we used the program
SURFER 4.0 (Golden Software Inc. Colorado,
kridging analyses).
Stable oxygen isotope ratios of the planktic
foraminifera were measured with a Finnigan MAT
251 mass spectrometer. The isotope composition is
expressed in the standard 8-notation, where
8 = (Rsample - Rstandard)/Rstandard * 1000 (R:
"0/ 16 0) relative to the Pee Dee belemnite (PDB)
standard. Because most of the towed individuals
are smaller than 250 I-lm, tbin-walled, and less abundant than in sediment samples (see Table 2), it was
often difficult to get enough individuals for an isotope measurement. For this reason it was only p~ssible to carry out single measurements of species
and/or size classes. Depending on the species and
size, 3 (for example the large and thick-walled G.
menardii 500-600 I-lm) to 70 (like the small and
rather thin-walled speciesG. ruberw. 125-250 I-lm)
individuals were used for one measurement.
Results and Discussion
Standing Stock in the Equatorial and
Eastern South Atlantic
Plankton tows from the South Equatorial Current,
South Equatorial Counter Current, Angola Current,