30
Weferetal.
be obtained using two or more species which live
at different depths or have their production maxima
at different seasons (Kroon and Ganssen 1989;
Steens et al. 1992). Schneider et al. (1994) used
the difference in Ol3C values between the two
planktic species G. ruber (pink) and G. bulloides
as a proxy for changes in upwelling and biological
productivity offthe Congo. Previous investigations
(Ganssen 1983; Kroon and Ganssen 1988; Curry
et al. 1992) have shown that the OJ3C values of G.
100
AGE (kyl)
,,.,
200
Fig. 17. Difference in /)I3C between G. ruber and G.
bulloides (t./)I3C) with time compared with marine organic carbon concentrations (MOC), mass accumulation
rates (MOC MAR) and paleoproductivity (GeoB core
1008-3, Zaire Fan). Shaded bars indicate correspondence
of minimum isotope differences and the other three parameters. From Schneider et al. (1994).
bulloides increase with higher productivity, and that
they become more negative in G. ruber with increased upwelling of 12C-rich subsurface waters.
The O J3 C difference found off the mouth of the
Congo (Zaire Fan) confirms the temporal pattern
that is obtained from the sedimentation pattern of
organic matter (Fig. 17).
Instead of using the difference between shallow-living and deep-living planktic foraminifers to
reconstruct thermocline fertility (and thickness of
the mixed layer), we can study the difference between planktic and benthic forms. This difference
will yield information about the general efficiency
of the ocean system in exporting organic carbon
("carbon pump efficiency"). A change between
glacial and interglacial periods in this proxy variable would indicate changes in overall nutrient content ofthe ocean (Broecker 1982). Locally, an increase in t.O'3C would suggest an increase in
stratification in upper waters, enhancing the contrast between shallow and deep water masses.
Differences in OJ3C between different species
of benthic foraminifers are also of interest. These
relate to porewater gradients, and hence to the intensity of oxidation of organic matter within the
sediment. This intensity is a function of organic
matter supply (Zahn et al. 1986). Therefore, the
':\"013C difference between benthics is a measure
of flux, that is, of productivity. For this purpose the
two species C. wuellerstorfi (epifaunal) and U.
peregrina (in faunal) may be used. McCorckle et
al. (\990) reported good agreement between the
OJ3C of the pore water (related to productivity)and
Ol3C in the carbonate tests of stained Uvigerina.
It has long been known that C. wuellerstorfi lives
on the sediment surface (Lutze and Thiel 1989), but
new studies in the Southern Ocean indicate that
OJ3C ofthis species is also influenced to some extent by particle rain, e.g. organic carbon fluxes
(Mackensen et al. 1993; Mackensen and Bickert
this volume).
To further examine productivity effects on
benthic OJ3C deviations, Bickert and Wefer (1999)
compared open ocean data with observations in the
Namibia upwelling area (Fig. 18).oI3CL c02 values as well as phosphate concentrations in water
samples of the Namibia upwelling area differ sig-
Weferetal.
be obtained using two or more species which live
at different depths or have their production maxima
at different seasons (Kroon and Ganssen 1989;
Steens et al. 1992). Schneider et al. (1994) used
the difference in Ol3C values between the two
planktic species G. ruber (pink) and G. bulloides
as a proxy for changes in upwelling and biological
productivity offthe Congo. Previous investigations
(Ganssen 1983; Kroon and Ganssen 1988; Curry
et al. 1992) have shown that the OJ3C values of G.
100
AGE (kyl)
,,.,
200
Fig. 17. Difference in /)I3C between G. ruber and G.
bulloides (t./)I3C) with time compared with marine organic carbon concentrations (MOC), mass accumulation
rates (MOC MAR) and paleoproductivity (GeoB core
1008-3, Zaire Fan). Shaded bars indicate correspondence
of minimum isotope differences and the other three parameters. From Schneider et al. (1994).
bulloides increase with higher productivity, and that
they become more negative in G. ruber with increased upwelling of 12C-rich subsurface waters.
The O J3 C difference found off the mouth of the
Congo (Zaire Fan) confirms the temporal pattern
that is obtained from the sedimentation pattern of
organic matter (Fig. 17).
Instead of using the difference between shallow-living and deep-living planktic foraminifers to
reconstruct thermocline fertility (and thickness of
the mixed layer), we can study the difference between planktic and benthic forms. This difference
will yield information about the general efficiency
of the ocean system in exporting organic carbon
("carbon pump efficiency"). A change between
glacial and interglacial periods in this proxy variable would indicate changes in overall nutrient content ofthe ocean (Broecker 1982). Locally, an increase in t.O'3C would suggest an increase in
stratification in upper waters, enhancing the contrast between shallow and deep water masses.
Differences in OJ3C between different species
of benthic foraminifers are also of interest. These
relate to porewater gradients, and hence to the intensity of oxidation of organic matter within the
sediment. This intensity is a function of organic
matter supply (Zahn et al. 1986). Therefore, the
':\"013C difference between benthics is a measure
of flux, that is, of productivity. For this purpose the
two species C. wuellerstorfi (epifaunal) and U.
peregrina (in faunal) may be used. McCorckle et
al. (\990) reported good agreement between the
OJ3C of the pore water (related to productivity)and
Ol3C in the carbonate tests of stained Uvigerina.
It has long been known that C. wuellerstorfi lives
on the sediment surface (Lutze and Thiel 1989), but
new studies in the Southern Ocean indicate that
OJ3C ofthis species is also influenced to some extent by particle rain, e.g. organic carbon fluxes
(Mackensen et al. 1993; Mackensen and Bickert
this volume).
To further examine productivity effects on
benthic OJ3C deviations, Bickert and Wefer (1999)
compared open ocean data with observations in the
Namibia upwelling area (Fig. 18).oI3CL c02 values as well as phosphate concentrations in water
samples of the Namibia upwelling area differ sig-