Examination of the Use of Biomarker Proxies for the Reconstruction of Paleoceanographic Conditions in the Northern North Atlantic

Biomarkers are organic mole cules synthesized by specific source organisms (e.g. phytoplankton, terrigenous plants) which survive depo sition to sediments in a recognizable form. They can thus be considered to be chemical fossils. In some cases, the source organism is very well constrained (e.g. bacteriochlorophyll d, from strictly anaerobic photosynthetic bacteria), although sometimes the source is more general (e.g. chlorophyll a derived from photosynthetic organ isms). The utility of these organic components as paleoproxies largely depends on their resilience to early degradation processes during sedimentation, which must be relatively high so that the component is found in the sedimentary column. For instance, (1993) argued that some of the more diagnostic components are sometimes the least stable, giving as an example the high lability of carotenoids (e.g. Repeta and Gagosian 1987) which have some of the higher biologic al specificity of most other lipid classes. Other factors, such as specificity of source s (broad vs. restricted), will constrain the type of application. For instance, n-alkanes distributions in marine sediments are often related to terrigenous higher plant material s, and their long-range transport by wind (e.g. Simoneit et al. 1977). Thus, these components have a global distribution, and the interpretation of the n-alkane data from a global vs. local source standpoint can be ambiguous, as their source and associated windvector may be very difficult to determine.