The South Atlantic Carbon Isotope Record of Planktic Foraminifera
S. Mulitza ' *, H. Arz', S. Kemle-von Mucke ' , C. MOOS', H.-S. Niebler , ,2,
J. Patzold ' and M. SegP
1 Universitat Bremen, Fachbereich Geowissenschaften, Postfach 33 04 40,
D-28334 Bremen, Germany
2 Alfred-Wegener-Institutfur Polar- und Meeresforschung, Postfach 12 01 61,
D-27515 Bremerhaven, Germany
*corresponding author (e-mail):smul@palmod.uni-bremen.de
Abstract: We reviewed the paleoceanographic application of the carbon isotope composition of
planktic foraminifera, Major controls on the distribution of Ol3C of dissolved CO, (ol3C,co) in the
modem ocean are photosynthesis-respiration cycle, isotopic fractionation during air-sea exchange,
and circulation, The carbon isotope composition of surface waters is not recorded without
perturbations by planktic foraminifera. Besides 0 13 C'C02 of the surrounding seawater, the 013C
composition of planktic foraminifera is affected by vital effects, the water depth of calcification and
postdepositional dissolution. We compared several high-resolution (> I Ocm/ka) carbon isotope
records from the Southern Ocean, the Benguela upwelling system, and the tropical Atlantic. In the
Southern Ocean, carbon isotope values are about 1.2 %0 lower during the LGM and up to 1.7 %0
lower during the last deglaciation, when compared to the Holocene. These depletions might be
explained with a combination of a subsurface nutrient enrichment and reduced air-sea exchange due
to an increased stratification of surface waters. In the Benguela Upwelling system, waters originating
in the south are upwelled. While the deglacial minimum is transferred and recorded in its full extent
in the 013C record of Globigerina bulloides, glacial values show only little changes. This might
suggest, that the lower glacial 013C values of high-latitude surface waters are not upwelled off
Namibia, or that G. bulloides records post-upwelling conditions, when increased seasonal production
has already increased surface-water OIlC. Synchronous to the O"C depletions in high latitudes, low
O"C values were recorded in Globigerinoides sacculifer during the LGM and during the last
deglaciation in the nutrient-depleted western equatorial Atlantic. Hence, part of the glacial-interglacial
variability presumably transferred from high to low latitudes seems to be related to changes in
thermodynamic fractionation. The variability in olle is lowest in the northernmost core M35003-4
from the eastern Caribbean, implying that the Antarctic Intermediate Water might have acted as a
conduit to transfer the deglacial minimum to tropical surface waters.
Introduction
During the Quaternary the climate of our planet Hence, additional feedback mechanisms must play
underwent a succession of cold periods in which an important role. Ice-core studies have shown that
large parts of the northern hemisphere were cov- part of the glacial cooling was presumably due to
ered by ice. Most scientists believe that variations lower atmospheric CO 2 contents. The origin ofthe
in the distribution of insolation are the major driv- glacial CO 2 decrease must lie in the ocean, because
ing force for the ice ages (Hays et al. 1976; Imbrie it is the largest active carbon reservoir and a key
et al. 1984). However, insolation alone cannot ex- component as a sink and a transfer agent for the
plain the amplitude and hemispheric synchronism motion of carbon through the world system. Conof the temperature changes (Short et al. 1991). sequently, in order to understand global climate
From FISCHER G, WEFER G (eds), 1999, Use of Proxies in Paleoceanography: Examplesfrom the South Atlantic. Springer-Verlag
Berlin Heidelberg, pp 427-445
S. Mulitza ' *, H. Arz', S. Kemle-von Mucke ' , C. MOOS', H.-S. Niebler , ,2,
J. Patzold ' and M. SegP
1 Universitat Bremen, Fachbereich Geowissenschaften, Postfach 33 04 40,
D-28334 Bremen, Germany
2 Alfred-Wegener-Institutfur Polar- und Meeresforschung, Postfach 12 01 61,
D-27515 Bremerhaven, Germany
*corresponding author (e-mail):smul@palmod.uni-bremen.de
Abstract: We reviewed the paleoceanographic application of the carbon isotope composition of
planktic foraminifera, Major controls on the distribution of Ol3C of dissolved CO, (ol3C,co) in the
modem ocean are photosynthesis-respiration cycle, isotopic fractionation during air-sea exchange,
and circulation, The carbon isotope composition of surface waters is not recorded without
perturbations by planktic foraminifera. Besides 0 13 C'C02 of the surrounding seawater, the 013C
composition of planktic foraminifera is affected by vital effects, the water depth of calcification and
postdepositional dissolution. We compared several high-resolution (> I Ocm/ka) carbon isotope
records from the Southern Ocean, the Benguela upwelling system, and the tropical Atlantic. In the
Southern Ocean, carbon isotope values are about 1.2 %0 lower during the LGM and up to 1.7 %0
lower during the last deglaciation, when compared to the Holocene. These depletions might be
explained with a combination of a subsurface nutrient enrichment and reduced air-sea exchange due
to an increased stratification of surface waters. In the Benguela Upwelling system, waters originating
in the south are upwelled. While the deglacial minimum is transferred and recorded in its full extent
in the 013C record of Globigerina bulloides, glacial values show only little changes. This might
suggest, that the lower glacial 013C values of high-latitude surface waters are not upwelled off
Namibia, or that G. bulloides records post-upwelling conditions, when increased seasonal production
has already increased surface-water OIlC. Synchronous to the O"C depletions in high latitudes, low
O"C values were recorded in Globigerinoides sacculifer during the LGM and during the last
deglaciation in the nutrient-depleted western equatorial Atlantic. Hence, part of the glacial-interglacial
variability presumably transferred from high to low latitudes seems to be related to changes in
thermodynamic fractionation. The variability in olle is lowest in the northernmost core M35003-4
from the eastern Caribbean, implying that the Antarctic Intermediate Water might have acted as a
conduit to transfer the deglacial minimum to tropical surface waters.
Introduction
During the Quaternary the climate of our planet Hence, additional feedback mechanisms must play
underwent a succession of cold periods in which an important role. Ice-core studies have shown that
large parts of the northern hemisphere were cov- part of the glacial cooling was presumably due to
ered by ice. Most scientists believe that variations lower atmospheric CO 2 contents. The origin ofthe
in the distribution of insolation are the major driv- glacial CO 2 decrease must lie in the ocean, because
ing force for the ice ages (Hays et al. 1976; Imbrie it is the largest active carbon reservoir and a key
et al. 1984). However, insolation alone cannot ex- component as a sink and a transfer agent for the
plain the amplitude and hemispheric synchronism motion of carbon through the world system. Conof the temperature changes (Short et al. 1991). sequently, in order to understand global climate
From FISCHER G, WEFER G (eds), 1999, Use of Proxies in Paleoceanography: Examplesfrom the South Atlantic. Springer-Verlag
Berlin Heidelberg, pp 427-445