442
Mulitza et al.
was taken at 12°N/61°W close to Barbados. In
fact, the difference between the Holocene (0-5 ka)
and the deglacial minimum (12.5-13.5 ka) amounts
to only 0.2 %0 in core M35003-4, and is much less
pronounced than in the G. sacculifer record from
GeoB 3104-1. This observation strongly supports
the hypothesis of a high southern origin of the
deglacial minimum.
The large glacial-interglacial variability of high
latitudes (e.g. core PSI768-8, Fig. 9a) is obviously
not transferred to lower latitudes to the same extent as the deglacial minimum. One explanation for
this observation could be the glacial circulation
pattern. Benthic 8 13 C values indicate that the glacial intermediate depth equatorial Atlantic was cut
off from the southern intermediate water source
(Oppo and Fairbanks 1987; Boyle and Keigwin
1987; Duplessy et al. 1988). Hence, there might
have been no effective conduit to transfer the highlatitude signal to the low latitudes.
Conclusions
The carbon isotope distribution in the ocean provides important information about the ocean's circulation state. The 8 13 C of shallow-dwelling
planktic foraminifera is an indispensable tool to define the preformed 8 13 C composition of past water masses. Besides the carbon isotope composition ofthe surrounding seawater, important controls
of the shell's 8 J3 C are (I) disequilibrium vital effects, (2) the habitat of the used species, and (3)
postdepositional dissolution. Vital effects vary from
species to species and cannot be reduced to a single mechanism. The carbonate system, photosynthesis, and the incorporation oflight metabolic cq
seem to be major candidates to explain disequilibrium effects. However, once resolved, vital effects
might provide additional proxies for temperature
and the carbonate system. Knowledge ofthe habitat is also critical for the interpretation ofthe8 J3 C
composition of planktic foraminifera. On the other
hand, if the depth of calcification is well known,
carbon isotope differences between foraminiferal
species can yield information about the nutrient
stratification of surface waters.
Low glacial 8 J3 C values in the Atlantic sector
of the Southern Ocean are presumably due to a
combination of decreased air-sea exchange, subsurface nutrient enrichment, and environmentally
controlled vital effects. At present, it seems to be
difficult to quantify the contribution ofthe different effects to the total record. The variability in the
oligotropic tropical Atlantic is much lower and
might by explained with a combination of global
variations and changes in the thermodynamic imprint of source waters. Despite their different
amplitudes, the ODC records from various parts in
the tropical and South Atlantic exhibit some striking similarities. An event common to both high and
low latitudes is the deglacial8 D C minimum near
13 ka. Our study shows that the deglacial minimum
is associated with huge hydrographic changes in the
Atlantic sector of the Southern Ocean just south
ofthe Polar Front. We have presented strong support for the hypothesis that the AAIW provides a
conduit to transfer the deglacial minimum from the
Antarctic surface to tropical Atlantic surface waters. However, to further strengthen this hypothesis, a more precise geographic pattern of 8 l3 C
variability is required.
Acknowledgments
The preparation ofthis paper was supported by EC
Grant CHRX-CT 92-0066 (received by S. Mulitza
during a postdoctoral stay at the Centre des Faibles
Radioactivites, Gif-sur-Yvette) and the Deutsche
Forschungsgemeinschaft (Sonderforschungsbereich 261 at University of Bremen; Contribution
Nr. 222). We thank E. Michel and an anonymous
referee for careful reviews and J. Bijma and R.R.
Schneider for discussion and comments. Thanks to
P. Grootes and staff of the Leibnitz-Labor in Kiel
for providing AMS- 1 4 C datings of core
M35003-4. Data available underwww.pangaea.del
Projects/SFB261.
References
Arz H, PatzoldJ, Wefer G (1998) Short-tenn climate fluctuations in the westem tropical Atlantic for the past
85,000 years revealed by a sediment core offNEBrazil. Quat Res 50: 157-166
Bard E (1988) Correction of accelerator mass
spectrometry 14C ages measured in planktonic
foraminifera: Paleoceanographic implications.
Mulitza et al.
was taken at 12°N/61°W close to Barbados. In
fact, the difference between the Holocene (0-5 ka)
and the deglacial minimum (12.5-13.5 ka) amounts
to only 0.2 %0 in core M35003-4, and is much less
pronounced than in the G. sacculifer record from
GeoB 3104-1. This observation strongly supports
the hypothesis of a high southern origin of the
deglacial minimum.
The large glacial-interglacial variability of high
latitudes (e.g. core PSI768-8, Fig. 9a) is obviously
not transferred to lower latitudes to the same extent as the deglacial minimum. One explanation for
this observation could be the glacial circulation
pattern. Benthic 8 13 C values indicate that the glacial intermediate depth equatorial Atlantic was cut
off from the southern intermediate water source
(Oppo and Fairbanks 1987; Boyle and Keigwin
1987; Duplessy et al. 1988). Hence, there might
have been no effective conduit to transfer the highlatitude signal to the low latitudes.
Conclusions
The carbon isotope distribution in the ocean provides important information about the ocean's circulation state. The 8 13 C of shallow-dwelling
planktic foraminifera is an indispensable tool to define the preformed 8 13 C composition of past water masses. Besides the carbon isotope composition ofthe surrounding seawater, important controls
of the shell's 8 J3 C are (I) disequilibrium vital effects, (2) the habitat of the used species, and (3)
postdepositional dissolution. Vital effects vary from
species to species and cannot be reduced to a single mechanism. The carbonate system, photosynthesis, and the incorporation oflight metabolic cq
seem to be major candidates to explain disequilibrium effects. However, once resolved, vital effects
might provide additional proxies for temperature
and the carbonate system. Knowledge ofthe habitat is also critical for the interpretation ofthe8 J3 C
composition of planktic foraminifera. On the other
hand, if the depth of calcification is well known,
carbon isotope differences between foraminiferal
species can yield information about the nutrient
stratification of surface waters.
Low glacial 8 J3 C values in the Atlantic sector
of the Southern Ocean are presumably due to a
combination of decreased air-sea exchange, subsurface nutrient enrichment, and environmentally
controlled vital effects. At present, it seems to be
difficult to quantify the contribution ofthe different effects to the total record. The variability in the
oligotropic tropical Atlantic is much lower and
might by explained with a combination of global
variations and changes in the thermodynamic imprint of source waters. Despite their different
amplitudes, the ODC records from various parts in
the tropical and South Atlantic exhibit some striking similarities. An event common to both high and
low latitudes is the deglacial8 D C minimum near
13 ka. Our study shows that the deglacial minimum
is associated with huge hydrographic changes in the
Atlantic sector of the Southern Ocean just south
ofthe Polar Front. We have presented strong support for the hypothesis that the AAIW provides a
conduit to transfer the deglacial minimum from the
Antarctic surface to tropical Atlantic surface waters. However, to further strengthen this hypothesis, a more precise geographic pattern of 8 l3 C
variability is required.
Acknowledgments
The preparation ofthis paper was supported by EC
Grant CHRX-CT 92-0066 (received by S. Mulitza
during a postdoctoral stay at the Centre des Faibles
Radioactivites, Gif-sur-Yvette) and the Deutsche
Forschungsgemeinschaft (Sonderforschungsbereich 261 at University of Bremen; Contribution
Nr. 222). We thank E. Michel and an anonymous
referee for careful reviews and J. Bijma and R.R.
Schneider for discussion and comments. Thanks to
P. Grootes and staff of the Leibnitz-Labor in Kiel
for providing AMS- 1 4 C datings of core
M35003-4. Data available underwww.pangaea.del
Projects/SFB261.
References
Arz H, PatzoldJ, Wefer G (1998) Short-tenn climate fluctuations in the westem tropical Atlantic for the past
85,000 years revealed by a sediment core offNEBrazil. Quat Res 50: 157-166
Bard E (1988) Correction of accelerator mass
spectrometry 14C ages measured in planktonic
foraminifera: Paleoceanographic implications.