Paper No. 1
Presentation Time: 1:00 PM


BUTTERFIELD, Nicholas J., Department of Earth Sciences, University of Cambridge, Downing Street, Cambridgeshire, Cambridge, CB2 3EQ, United Kingdom,

Plankton and plankton dynamics have changed profoundly over the past four billion years, including a fundamental change of state through the Cryogenian-Ediacaran-Cambrian transition. Whereas Proterozoic export production was dominated by small, inherently buoyant cyanobacteria, leading to relatively stratified turbid-water conditions, its Phanerozoic counterpart is represented by large, often biomineralizing eukaryotic phytoplankton associated with rapid export and a well aerated water column. In modern aquatic systems these qualities represent alternative stable states maintained through positive plankton-environment feedbacks, typically mediated by the feeding activities of suspension feeding metazoans. The same was true in the mid-Neoproterozoic, except that metazoans had yet to evolve most of their modern feeding repertoires (and associated co-evolutionary and engineering effects on eukaryotic phytoplankton). The earliest sign of Phanerozoic-style plankton dynamics appears around 750 Ma with the first quantitative occurrence of eukaryotic biomarkers and a distinctive new range of eukaryotic microfossils. This modal shift is intriguingly coincident with recent molecular clock estimates for the first appearance of animals, and there is a good case for recognizing early sponge-grade suspension feeding as an important selective agent for larger, more export prone phytoplankton - leading to fundamental changes in the biological pump, oceanic ventilation, and possibly global climate. Further co-evolutionary innovations in the plankton would have accompanied the muscle-based suspension feeding of cnidarians-grade animals; however, the most profound effects were undoubtedly induced by the explosive radiation of bilaterians in the early Cambrian (ca. 530 Ma). The unique capacity of motile metazoans with a through-gut to build multi-trophic food webs, drive co-evolutionary diversification, and actively trans-locate nutrients between the plankton and benthos revolutionized the marine biosphere.