Oxygen Isotope Values of Planktic Foraminifera
173
ratios than adult individuals (Berger et al. 1978) at
all six stations. Most foraminifera sink in the water-column during ontogeny (Bijma and Hemleben
1994), therefore the 0 18 0 oal . of adult individuals
reflects the conditions of de~per and cooler surface
water layers.
The following description of depth habitats is
structured in the order ofthe species temperaturedependent appearance from north to south, i.e.
from the tropical to the polar zone. It should be
noted that most studies on the depth habitat of
planktic foraminifera were carried out for the warm
water region (summaries in Berger 1969; Be 1977;
Hemleben and Spindler 1983; Deuser and Ross
1989; Ottens 1992). The apparent calcification
depths determined in this study are valid for the
South Atlantic Ocean with its specific oceanographic conditions. However, comparing our results
with literature data we keep in mind that depth
habitats can change substancially from region to region substantially.
Warm-Water Region
The tropical species Sphaeroidinella dehiscens
occurs only at the Walvis Ridge station (Fig. 3).
Adult specimens have isotopic values, which correspond to water values in the first 50 m of the
water column. This calcification depth agrees with
data of Be (1977), who describes a depth habitat
ofless than 100 m water depth.
Pulleniatina obliquiloculata also occurs only
in the subtropical part ofthe area investigated (Figs.
3,4) and calcifies in a water depth between 0 to
100 m, ifthe range of "oxygen isotope disequilibrium" is considered (Table 2). This depth is equal
to the depth habitat observed by Be (1977), who
found maximum occurrences between 50 and 100
m.
The subtropical species Globigerinoides
conglobatus was found exclusively at station
PS2230-110cated at the South African continental
slope west of the Cape of Good Hope (Fig. 4).
Taking into account the reported range of "oxygen
isotope disequilibrium" (Table 2),G. conglobatus
calcifies in a water depth between 50 and 100 m.
This depth confirms results of Be (1977), who described a depth habitat of> 50 m.
The species Globorotalia menardii and
Globorotalia tumida have a similar morphology
and a comparable calcifying depth. Both species
are restricted to the subtropical part of the South
Atlantic Ocean, but G. menardii also occurs in the
area of the Subtropical Front (Figs. 3-5). Both
Globorotaliae calcify in a depth between 50 m and
250 m (applying the "oxygen isotope disequilibrium",
Table 2) and only individuals in neanic stage seem
to calcify at a shallower water depth. These results
confirm the depth reports of Be (1977) and the tow
investigations in the South Atlantic Ocean by
Kemle v. Miicke and Oberhansli (this volume).
Jones (1967) and Oberhiinsli et al. (1992) previously described the preference of G. menardii for
a deep habitat (50 m to 200 m).
Globigerinoides sacculifer (with and without
sac-like chamber) occurs in the area ofthe Subtropical Front and north of it , in the Subtropical Gyre.
Literature data related to the "oxygen isotope disequilibrium" varies strongly (Table 2). When we use
a mean "oxygen isotope disequilibrium" of -OJ %0,
G. sacculifer calcifies mainly in a water depth between 0 and 30 m (Figs. 3-5). This agrees with the
results of Be (1977) and the tow investigations of
Kemle v. Miicke and Oberhansli (this volume) in
the South Atlantic Ocean, which described a main
occurrence between 0 and 50 m water depth. As
for the North Atlantic Ocean, Ottens (1992) also
describes the upper 50 m as the depth preference
for G. sacculifer. Hemleben and Spindler (1983),
however, found a slightly deeper habitat at 0 to 80
m water depth, which was confirmed by studies on
population dynamics by Bijma and Hemleben
(1994). If a stronger "oxygen isotope disequilibrium" is taken into account, the calcification depth
of G. sacculifer would be between 30 and 80 m.
Duplessy et al. (1981) have demonstrated that, due
to gametogenic calcification in deeper and cooler
surface waters below the euphotic zone, the shells
accumulate 18 0. Lohmann (1995) suggests from
modelling an additional crust-calcification at about
100 m water depth. Kahn (1979) describes a trend
to signifcant lighter oxygen isotope values for G.
sacculiferwith a sac-like formed last chamber, but
that trend was not observed here, as both
morphotypes showed nearly identicalo180ealdl.
values.
173
ratios than adult individuals (Berger et al. 1978) at
all six stations. Most foraminifera sink in the water-column during ontogeny (Bijma and Hemleben
1994), therefore the 0 18 0 oal . of adult individuals
reflects the conditions of de~per and cooler surface
water layers.
The following description of depth habitats is
structured in the order ofthe species temperaturedependent appearance from north to south, i.e.
from the tropical to the polar zone. It should be
noted that most studies on the depth habitat of
planktic foraminifera were carried out for the warm
water region (summaries in Berger 1969; Be 1977;
Hemleben and Spindler 1983; Deuser and Ross
1989; Ottens 1992). The apparent calcification
depths determined in this study are valid for the
South Atlantic Ocean with its specific oceanographic conditions. However, comparing our results
with literature data we keep in mind that depth
habitats can change substancially from region to region substantially.
Warm-Water Region
The tropical species Sphaeroidinella dehiscens
occurs only at the Walvis Ridge station (Fig. 3).
Adult specimens have isotopic values, which correspond to water values in the first 50 m of the
water column. This calcification depth agrees with
data of Be (1977), who describes a depth habitat
ofless than 100 m water depth.
Pulleniatina obliquiloculata also occurs only
in the subtropical part ofthe area investigated (Figs.
3,4) and calcifies in a water depth between 0 to
100 m, ifthe range of "oxygen isotope disequilibrium" is considered (Table 2). This depth is equal
to the depth habitat observed by Be (1977), who
found maximum occurrences between 50 and 100
m.
The subtropical species Globigerinoides
conglobatus was found exclusively at station
PS2230-110cated at the South African continental
slope west of the Cape of Good Hope (Fig. 4).
Taking into account the reported range of "oxygen
isotope disequilibrium" (Table 2),G. conglobatus
calcifies in a water depth between 50 and 100 m.
This depth confirms results of Be (1977), who described a depth habitat of> 50 m.
The species Globorotalia menardii and
Globorotalia tumida have a similar morphology
and a comparable calcifying depth. Both species
are restricted to the subtropical part of the South
Atlantic Ocean, but G. menardii also occurs in the
area of the Subtropical Front (Figs. 3-5). Both
Globorotaliae calcify in a depth between 50 m and
250 m (applying the "oxygen isotope disequilibrium",
Table 2) and only individuals in neanic stage seem
to calcify at a shallower water depth. These results
confirm the depth reports of Be (1977) and the tow
investigations in the South Atlantic Ocean by
Kemle v. Miicke and Oberhansli (this volume).
Jones (1967) and Oberhiinsli et al. (1992) previously described the preference of G. menardii for
a deep habitat (50 m to 200 m).
Globigerinoides sacculifer (with and without
sac-like chamber) occurs in the area ofthe Subtropical Front and north of it , in the Subtropical Gyre.
Literature data related to the "oxygen isotope disequilibrium" varies strongly (Table 2). When we use
a mean "oxygen isotope disequilibrium" of -OJ %0,
G. sacculifer calcifies mainly in a water depth between 0 and 30 m (Figs. 3-5). This agrees with the
results of Be (1977) and the tow investigations of
Kemle v. Miicke and Oberhansli (this volume) in
the South Atlantic Ocean, which described a main
occurrence between 0 and 50 m water depth. As
for the North Atlantic Ocean, Ottens (1992) also
describes the upper 50 m as the depth preference
for G. sacculifer. Hemleben and Spindler (1983),
however, found a slightly deeper habitat at 0 to 80
m water depth, which was confirmed by studies on
population dynamics by Bijma and Hemleben
(1994). If a stronger "oxygen isotope disequilibrium" is taken into account, the calcification depth
of G. sacculifer would be between 30 and 80 m.
Duplessy et al. (1981) have demonstrated that, due
to gametogenic calcification in deeper and cooler
surface waters below the euphotic zone, the shells
accumulate 18 0. Lohmann (1995) suggests from
modelling an additional crust-calcification at about
100 m water depth. Kahn (1979) describes a trend
to signifcant lighter oxygen isotope values for G.
sacculiferwith a sac-like formed last chamber, but
that trend was not observed here, as both
morphotypes showed nearly identicalo180ealdl.
values.