Chapter 19
Palaeoenvironmental Reconstructions Using
Stable Carbon Isotopes and Organic Biomarkers
S.Wakeham
19.1
Introduction
Aquatic sediments carry the potential of preserving a historical record, or some remnant thereof, of past environmental conditions. The stratigraphic record has long been
a tool for elucidating the character of the Earth and the forces that have altered its
face and determined the nature, distributions and fate of living organisms. There have
been dramatic changes in the Earth's climate in the past. Increasing levels of atmospheric CO 2 attributed to combustion of biomass and fossil fuels coupled with deforestation have heightened societal and scientific concerns about global warming, a reduction in ice volume and a rise in sea level. These issues have generated a greater
interest in understanding past natural and present anthropogenic processes that influence global climate change and in developing predictive capabilities about future
climate.
Studies of palaeoenvironment have varied in scope. They can range from qualitative descriptions and interpretation of conditions at a given time in the geological past
to quantitative investigations concerned with the nature and the rate of change during specific time intervals. Organic biomarkers, molecules whose molecular structures
point to specific biological sources, are proving to be quite valuable for palaeoenvironmental reconstructions. The utility of biomarkers derives from two features. First,
organisms that inhabit specific ecological niches may biosynthesize unique biomarker
compounds that can be used as indicators of the source organisms and their habitat.
Second, organisms often possess an ability to regulate patterns of constituent
biochemicals in order to remain viable under changing environmental conditions, so
that environmental characteristics may be inferred from these patterns. To be a robust
palaeoenvironmental proxy, the signal carried by biomarkers must survive during
deposition and burial in sediments over the time frame of interest.
This chapter discusses several ways that palaeoenvironmental records may be obtained from organic geochemical studies, in particular from biomarker records in the
sediment. The case studies represent only a few of the many applications that are presently accumulating in the literature and are by no means an exhaustive survey. Readers are referred to the references cited in the respective examples for further reading.
19.2
Stable Carbon Isotopes to Identify Organic Matter Sources
The biological source of sedimentary organic matter may be deduced from chemical
studies on the structure of individual compounds (biomarkers) extracted from sedi-
Palaeoenvironmental Reconstructions Using
Stable Carbon Isotopes and Organic Biomarkers
S.Wakeham
19.1
Introduction
Aquatic sediments carry the potential of preserving a historical record, or some remnant thereof, of past environmental conditions. The stratigraphic record has long been
a tool for elucidating the character of the Earth and the forces that have altered its
face and determined the nature, distributions and fate of living organisms. There have
been dramatic changes in the Earth's climate in the past. Increasing levels of atmospheric CO 2 attributed to combustion of biomass and fossil fuels coupled with deforestation have heightened societal and scientific concerns about global warming, a reduction in ice volume and a rise in sea level. These issues have generated a greater
interest in understanding past natural and present anthropogenic processes that influence global climate change and in developing predictive capabilities about future
climate.
Studies of palaeoenvironment have varied in scope. They can range from qualitative descriptions and interpretation of conditions at a given time in the geological past
to quantitative investigations concerned with the nature and the rate of change during specific time intervals. Organic biomarkers, molecules whose molecular structures
point to specific biological sources, are proving to be quite valuable for palaeoenvironmental reconstructions. The utility of biomarkers derives from two features. First,
organisms that inhabit specific ecological niches may biosynthesize unique biomarker
compounds that can be used as indicators of the source organisms and their habitat.
Second, organisms often possess an ability to regulate patterns of constituent
biochemicals in order to remain viable under changing environmental conditions, so
that environmental characteristics may be inferred from these patterns. To be a robust
palaeoenvironmental proxy, the signal carried by biomarkers must survive during
deposition and burial in sediments over the time frame of interest.
This chapter discusses several ways that palaeoenvironmental records may be obtained from organic geochemical studies, in particular from biomarker records in the
sediment. The case studies represent only a few of the many applications that are presently accumulating in the literature and are by no means an exhaustive survey. Readers are referred to the references cited in the respective examples for further reading.
19.2
Stable Carbon Isotopes to Identify Organic Matter Sources
The biological source of sedimentary organic matter may be deduced from chemical
studies on the structure of individual compounds (biomarkers) extracted from sedi-