CHAPTER 19 . Palaeoenvironmental Reconstructions
441
biomarkers can be caused by many factors, most of which are poorly constrained in
palaeoenvironmental studies but which are being intensely studied in the contemporary ocean (e.g. Popp et al. 1999). Carbon isotope fractionation is strongly influenced
by several factors in addition to dissolved CO2, One must be certain that the source of
the specific biomarker being used is as unambiguous as possible. The limited sources
of alkenones in open ocean settings - E. huxleyi and G. oceanica - makes these compounds among the best in the organic geochemists' toolbox to date. The carbon uptake mechanism and cellular geometry of source organisms must be known, because
they affect the lOp that is imprinted into organic matter. Microalgal growth rate is another important factor affecting lOp that cannot be easily determined in ancient environments. Cd/Ca ratios might be a proxy for surface water phosphate, which could be
used to infer primary production and perhaps growth rates. It is thus important to
use a multi-proxy approach - e.g. lOp determined from sedimentary alkenones and inorganic carbonate from planktonic foraminifera along with Cd/Ca measurements -
in order to improve confidence in the results.
Acknowledgements
The support of the National Science Foundation during the preparation of this paper
is gratefully acknowledged. C. Lee provided helpful comments to improve the manuscript.
References
Bird MI, Summons RE, Gagan MK, Roksandic Z, Dowling L, Head J, Fifield LK, Cresswell RG, Johnson
DP (1995) Terrestrial vegetation change inferred from n-alkane "l3C analysis in the marine environment. Geochim Cosmochim Acta 59:2853-2857
Boon JJ, Meer FW van der, Lange F de, Leeuw JW de, Schenck PA, Burlingame AL (1978) In: Initial reports of the Deep-Sea Drilling Project, vols 38,39,40 and 41, Supplement, Walvis Ridge DSDP Leg 40.
U.S. Government Printing Office, Washington, pp 627-637
Brassell SC (1993) Applications of biomarkers for delineating marine paleoclimate fluctuations during
the Pleistocene. In: Engel MH, Macko SA (eds) Organic geochemistry - principles and applications.
Plenum Press, New York, pp 699-738
Brassell SC, Eglinton G, Marlowe IT, pflaumann U, Sarnthein M (1986) Molecular stratigraphy: A new
tool for climate assessment. Nature 320:129-133
Calvert SE, Pederson TF (1992) Organic carbon accumulation and preservation in marine sediments:
How important is anoxia? In: Whelan J, Farrington JW (eds) Organic matter. Univ. Press, New York,
pp 231- 263
Conte MH, Volkman JK, Eglinton G (1994) Lipid biomarkers of the Haptophyta. In: Green JC, Leadbeater
BSC (eds) The haptophyte algae. Clarendon Press, Oxford, pp 351-377
Conte MH, Thompson A, Eglinton G, Green JC (1995) Lipid biomarkers diversity in the coccolithophoride
Emiliania huxleyi (Prymnesiophyceae) and the related species Gephyrocapsa oceanica. J Phycol
31:272- 282
Degens, ET (1969) Biogeochemistry of stable carbon isotopes. In: Eglinton G, Murphy MTJ (eds) Organic
geochemistry. Springer-Verlag, New York, pp 304-329
Demaison GJ, Moore GT (1980) Anoxic environments and oil source bed genesis. AAPG Bull
64:1179-1209
Emerson S, Hedges JI (1988) Processes controlling the organic carbon content of open ocean sediments.
Paleoceanogr 3:621-634
Freeman KH, Hayes JM (1992) Fractionation of carbon isotopes by phytoplankton and estimates of ancient CO2 levels. Global Biogeochem Cycles 6:185-198
Fogel ML, Cifuentes LA (1993) Isotope fractionation during primary production. In: Engel MH, Macko
SA (eds) Organic geochemistry - principles and applications. Plenum Press, New York, pp 73-98
Gearing P, Plucker FE, Parker PL (1977) Organic carbon stable isotope ratios in continental sediments.
Mar Chern 5:251-266
441
biomarkers can be caused by many factors, most of which are poorly constrained in
palaeoenvironmental studies but which are being intensely studied in the contemporary ocean (e.g. Popp et al. 1999). Carbon isotope fractionation is strongly influenced
by several factors in addition to dissolved CO2, One must be certain that the source of
the specific biomarker being used is as unambiguous as possible. The limited sources
of alkenones in open ocean settings - E. huxleyi and G. oceanica - makes these compounds among the best in the organic geochemists' toolbox to date. The carbon uptake mechanism and cellular geometry of source organisms must be known, because
they affect the lOp that is imprinted into organic matter. Microalgal growth rate is another important factor affecting lOp that cannot be easily determined in ancient environments. Cd/Ca ratios might be a proxy for surface water phosphate, which could be
used to infer primary production and perhaps growth rates. It is thus important to
use a multi-proxy approach - e.g. lOp determined from sedimentary alkenones and inorganic carbonate from planktonic foraminifera along with Cd/Ca measurements -
in order to improve confidence in the results.
Acknowledgements
The support of the National Science Foundation during the preparation of this paper
is gratefully acknowledged. C. Lee provided helpful comments to improve the manuscript.
References
Bird MI, Summons RE, Gagan MK, Roksandic Z, Dowling L, Head J, Fifield LK, Cresswell RG, Johnson
DP (1995) Terrestrial vegetation change inferred from n-alkane "l3C analysis in the marine environment. Geochim Cosmochim Acta 59:2853-2857
Boon JJ, Meer FW van der, Lange F de, Leeuw JW de, Schenck PA, Burlingame AL (1978) In: Initial reports of the Deep-Sea Drilling Project, vols 38,39,40 and 41, Supplement, Walvis Ridge DSDP Leg 40.
U.S. Government Printing Office, Washington, pp 627-637
Brassell SC (1993) Applications of biomarkers for delineating marine paleoclimate fluctuations during
the Pleistocene. In: Engel MH, Macko SA (eds) Organic geochemistry - principles and applications.
Plenum Press, New York, pp 699-738
Brassell SC, Eglinton G, Marlowe IT, pflaumann U, Sarnthein M (1986) Molecular stratigraphy: A new
tool for climate assessment. Nature 320:129-133
Calvert SE, Pederson TF (1992) Organic carbon accumulation and preservation in marine sediments:
How important is anoxia? In: Whelan J, Farrington JW (eds) Organic matter. Univ. Press, New York,
pp 231- 263
Conte MH, Volkman JK, Eglinton G (1994) Lipid biomarkers of the Haptophyta. In: Green JC, Leadbeater
BSC (eds) The haptophyte algae. Clarendon Press, Oxford, pp 351-377
Conte MH, Thompson A, Eglinton G, Green JC (1995) Lipid biomarkers diversity in the coccolithophoride
Emiliania huxleyi (Prymnesiophyceae) and the related species Gephyrocapsa oceanica. J Phycol
31:272- 282
Degens, ET (1969) Biogeochemistry of stable carbon isotopes. In: Eglinton G, Murphy MTJ (eds) Organic
geochemistry. Springer-Verlag, New York, pp 304-329
Demaison GJ, Moore GT (1980) Anoxic environments and oil source bed genesis. AAPG Bull
64:1179-1209
Emerson S, Hedges JI (1988) Processes controlling the organic carbon content of open ocean sediments.
Paleoceanogr 3:621-634
Freeman KH, Hayes JM (1992) Fractionation of carbon isotopes by phytoplankton and estimates of ancient CO2 levels. Global Biogeochem Cycles 6:185-198
Fogel ML, Cifuentes LA (1993) Isotope fractionation during primary production. In: Engel MH, Macko
SA (eds) Organic geochemistry - principles and applications. Plenum Press, New York, pp 73-98
Gearing P, Plucker FE, Parker PL (1977) Organic carbon stable isotope ratios in continental sediments.
Mar Chern 5:251-266