484
Andersen et al.
zooplankton herbivory (Grice et al. 1998). Furthermore, calkeno",' needed for calculations, is not effected by growth rate and its value is well known
(Popp et al. 1998a). In contrast to the bulk sediment 8 13 C, alkenone c p is also not influenced by
heterotrophic or terrigenious contributions (Popp et
al. 1997). However, a simple correlation between
alkenone c p and [C0 2 (aq)] is lacking, and the strong
b-P0 4 relationship indicates that growth rate was
an important effect on alkenone C p. Since there are
several factors, like denitrification and sedimentary
diagenetic alterations, which can invalidate the use
of 8 l5 N as a proxy for ancient b-values, other possible proxies for the b-value must also be tested in
the future. For instance, the Cd/Ca ratios in planktonic foraminifera were assumed by Bidigare et al.
(1997). For both alkenone c p and bulk sediment
8 13 C, some uncertainties arise if core-top samples
are calibrated because the difference between
modern PC0 2 and pre-industrial PC0 2 must be
assumed, as in our study a constant difference of
70 ppmv. In the future, more studies are needed to
evaluate this difference for different ocean areas.
For estimates of ancientPC0 2 using alkenone c r '
we also assume that the b-P0 4 relationship derived
from core-top samples remains constant through
time. We have no proof for any change, but some
change may coincide with flora changes of the
alkenone producers. As a consequence ofthis, the
calculated error of the PC0 2 estimate might be
higher if drastic floral changes have occured in the
past. Thus, we conclude that the alkenone c p -
method offers a good opportunity for estimating
ancient PC0 2 but additional studies are needed to
improve this tool in the future.
Acknowledgments
We thank Tim Freudenthal, Ralph Kreutz, Istvan
Pesza, and Monika Segl for technical assistance in
the extraction and the mass spectrometry laboratories. We are also grateful to Albert Benthien, Jelle
Bijma, Gerhard Fischer, Kai-Uwe Hinrichs, John
P. Jasper, Greg H. Rau, Abhijit Sanyal and one
anonymous reviewer for helpful discussions and
critical comments made on an earlier version of the
manuscript. We thank Hilary Paul for improving
the English. This research was funded by the
Bundesminister flir Bildung, Wissenschaft,
Forschung and Techno-Iogie (BMBF) and by the
Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 261 at Bremen University, Contribution No. 230). Data are available under
www.pangaea.de/Projects/SFB261.
References
Altabet MA, Fran~ois R (1994) Sedimentary nitrogen
isotopic ratio as a recorder for surface ocean nitrate
utilization. Global Biogeochem Cycles 8: 103-116
Altabet MA, Franyois R, Murray DW, Prell WL (1995)
Climate related variations in denitrification in the
Arabian Sea from sediment l5N/14N ratios. Nature
373: 506-509
Arthur MA, Dean WE, Claypool GE (1985) Anomalous
13C enrichment in modem marine organic carbon.
Nature315: 216-218
Badger MR, BassetM, Comins HN (1985) A model for
HCO; accumulation and photosynthesis in the
cyanobacterium Synechococcus sp. Plant Physiol 77:
465471
Bamola JM, Raynaud D, Korotkevich YS, Lorius L (1987)
Vostok ice core provides 160,000-year record of
atmospheric CO,. Nature 329: 408-414
Bennekom van AJ, Berger GW (1984) Hydrography
and silica budget of the Angola Basin. Geol Soc Amer
Mem 143: 1-134
Bentaleb I, Fontugne M, Descolas-Gros C, Girardin C,
Mariotti A, Pierre C, Brunet C, Poisson A (1996)
Organic carbon isotopic composition of phytoplankton and sea-surface PCO, reconstructions in
the Southern Indian Ocean during the last 50,000 yr.
Org Geochem 24: 399-410
BergerWH, SmetacekV, WeferG (eds) (1989) Productivity of the Ocean: Present and Past. J Wiley & Sons,
Chichester, pp 1-470
Bertrand P, Shinunield G, Martinez P, GroussetF, Jorissen
F, Pateme M, Pujol C, Bouloubassi I, Buat Menard
P, Peypouquet J-P, Beaufort L, Sicre M-A, LallierVerges E, Foster JM, Ternois Y (1996) The glacial
ocean productivity hypothesis: the importance of
regional temporal and spatial studies. Mar Geo1130:
1-9
Bidigare RR, Fluegge A, Freeman KH, Hanson KL,
Hayes JM, Hollander D, Jasper JP, King LL, Laws
EA, Milder J, Millero FJ, Pancost R, Popp BN,
Steinberg PA, Wakeham SG (1997) Consistent
fractionation of DC in nature and in the laboratory:
Growth-rate effects in some haptophyte algae.
Global Biogeochem Cycles 11: 279-292
Andersen et al.
zooplankton herbivory (Grice et al. 1998). Furthermore, calkeno",' needed for calculations, is not effected by growth rate and its value is well known
(Popp et al. 1998a). In contrast to the bulk sediment 8 13 C, alkenone c p is also not influenced by
heterotrophic or terrigenious contributions (Popp et
al. 1997). However, a simple correlation between
alkenone c p and [C0 2 (aq)] is lacking, and the strong
b-P0 4 relationship indicates that growth rate was
an important effect on alkenone C p. Since there are
several factors, like denitrification and sedimentary
diagenetic alterations, which can invalidate the use
of 8 l5 N as a proxy for ancient b-values, other possible proxies for the b-value must also be tested in
the future. For instance, the Cd/Ca ratios in planktonic foraminifera were assumed by Bidigare et al.
(1997). For both alkenone c p and bulk sediment
8 13 C, some uncertainties arise if core-top samples
are calibrated because the difference between
modern PC0 2 and pre-industrial PC0 2 must be
assumed, as in our study a constant difference of
70 ppmv. In the future, more studies are needed to
evaluate this difference for different ocean areas.
For estimates of ancientPC0 2 using alkenone c r '
we also assume that the b-P0 4 relationship derived
from core-top samples remains constant through
time. We have no proof for any change, but some
change may coincide with flora changes of the
alkenone producers. As a consequence ofthis, the
calculated error of the PC0 2 estimate might be
higher if drastic floral changes have occured in the
past. Thus, we conclude that the alkenone c p -
method offers a good opportunity for estimating
ancient PC0 2 but additional studies are needed to
improve this tool in the future.
Acknowledgments
We thank Tim Freudenthal, Ralph Kreutz, Istvan
Pesza, and Monika Segl for technical assistance in
the extraction and the mass spectrometry laboratories. We are also grateful to Albert Benthien, Jelle
Bijma, Gerhard Fischer, Kai-Uwe Hinrichs, John
P. Jasper, Greg H. Rau, Abhijit Sanyal and one
anonymous reviewer for helpful discussions and
critical comments made on an earlier version of the
manuscript. We thank Hilary Paul for improving
the English. This research was funded by the
Bundesminister flir Bildung, Wissenschaft,
Forschung and Techno-Iogie (BMBF) and by the
Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 261 at Bremen University, Contribution No. 230). Data are available under
www.pangaea.de/Projects/SFB261.
References
Altabet MA, Fran~ois R (1994) Sedimentary nitrogen
isotopic ratio as a recorder for surface ocean nitrate
utilization. Global Biogeochem Cycles 8: 103-116
Altabet MA, Franyois R, Murray DW, Prell WL (1995)
Climate related variations in denitrification in the
Arabian Sea from sediment l5N/14N ratios. Nature
373: 506-509
Arthur MA, Dean WE, Claypool GE (1985) Anomalous
13C enrichment in modem marine organic carbon.
Nature315: 216-218
Badger MR, BassetM, Comins HN (1985) A model for
HCO; accumulation and photosynthesis in the
cyanobacterium Synechococcus sp. Plant Physiol 77:
465471
Bamola JM, Raynaud D, Korotkevich YS, Lorius L (1987)
Vostok ice core provides 160,000-year record of
atmospheric CO,. Nature 329: 408-414
Bennekom van AJ, Berger GW (1984) Hydrography
and silica budget of the Angola Basin. Geol Soc Amer
Mem 143: 1-134
Bentaleb I, Fontugne M, Descolas-Gros C, Girardin C,
Mariotti A, Pierre C, Brunet C, Poisson A (1996)
Organic carbon isotopic composition of phytoplankton and sea-surface PCO, reconstructions in
the Southern Indian Ocean during the last 50,000 yr.
Org Geochem 24: 399-410
BergerWH, SmetacekV, WeferG (eds) (1989) Productivity of the Ocean: Present and Past. J Wiley & Sons,
Chichester, pp 1-470
Bertrand P, Shinunield G, Martinez P, GroussetF, Jorissen
F, Pateme M, Pujol C, Bouloubassi I, Buat Menard
P, Peypouquet J-P, Beaufort L, Sicre M-A, LallierVerges E, Foster JM, Ternois Y (1996) The glacial
ocean productivity hypothesis: the importance of
regional temporal and spatial studies. Mar Geo1130:
1-9
Bidigare RR, Fluegge A, Freeman KH, Hanson KL,
Hayes JM, Hollander D, Jasper JP, King LL, Laws
EA, Milder J, Millero FJ, Pancost R, Popp BN,
Steinberg PA, Wakeham SG (1997) Consistent
fractionation of DC in nature and in the laboratory:
Growth-rate effects in some haptophyte algae.
Global Biogeochem Cycles 11: 279-292