4 - Calcareous nannoplankton and global climate change

Summary

INTRODUCTION – THE NATURE OF NANNOPLANKTON

Calcareous nannofossils are the smallest (typically 5–10 μm in length), routinely studied fossils. In a pure nannofossil chalk, they are present in concentrations of several billions to a gram. They include coccoliths, the definite remains of coccolithophorid algae, and nannoliths, such as discoasters and nannoconids, which are of similar size and composition but which have less-certain biological affinities. Coccoliths play a major role in global climate-change research. This is partly because they are one of the most widely distributed, biostratigraphically useful groups in pelagic (both shelf and oceanic) environments, and have thus acted as primary chronometers for palaeoceanographical studies from the Late Triassic to the Recent. However, in addition to this, they constitute a valuable tool with which to monitor global change, through the study of accumulation rates, diversity and distribution changes, stable isotopes, and organic biomarkers. Furthermore, and most intriguingly, coccolithophores may be major agents of global change through their intimate relationship with the carbon cycle. Although minute individually, nannoplankton are highly visible en masse, producing blooms that are detectable from space (Holligan et al., 1983), and vast accumulations of pelagic sediment (most notably the Late Cretaceous chalks) which crop out in most parts of the world. These properties have combined to draw considerable attention from global change studies (e.g. Charlson et al., 1987; Lovelock, 1991).