The palaeoclimatic utility of terrestrial biomarkers in marine sediments

Organic compounds of known biological origin (biomarkers) and preserved in marine sediments have commonly been used to develop proxy records for past climate. While biomarkers for marine organisms are the logical target of many investigations, higher plant and other terrestrial biomarkers are also common in marine sediments and can be used to develop records of past continental vegetation, from which climatic change can be inferred. In fact, the high sampling resolution and extensive temporal record (>100 ma) of marine sediments, combined with the fact that compounds in marine sediments are delivered from a potentially vast geographical area, means that marine sediments can be more appropriate for such investigations than comparable terrestrial sedimentary sequences (lacustrine sediments, peats). Critical challenges to this approach include elucidation of the controls on delivery of organic material to marine sediments, ecological and physiological variability in biomarker distributions and isotopic compositions and the impact of diagenetic alteration on biomarker distributions. Here, we review potential terrestrial plant and microbial biomarkers, the controls on their carbon isotopic compositions and their modes of delivery to marine sediments, devoting specific attention to their utility in continental vegetation reconstruction.