Plankton evolution during peak greenhouse climates

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Calcareous nannoplankton are microscopic marine algae that secrete calcitic cell coverings (coccoliths) which are preserved throughout the geographically-widespread pelagic sedimentary record. By studying calcareous nannofossil assemblages preserved within sediments we can document their evolution through time, including changing diversity, rates of speciation and extinction, and population compositions. Calcareous nannoplankton are very responsive to changes in environmental parameters, particularly sea surface temperature and nutrient availability, with individual species or groups exhibiting particular preferences for specific ecological niches. Using the quantitative abundance of species within an assemblage we are therefore able to reconstruct past environmental conditions for a specific location at a given time. International Ocean Discovery Program Expedition 371 will drill deep-sea sediments in the Southwest Pacific Ocean, recovering cores which are from the Eocene epoch, a key interval in Earth's climate history marking the transition from very warm 'greenhouse' climates into a much cooler 'icehouse' world with large Antarctic icesheets. This profound interval of climatic change saw major shifts in physical, chemical and biological parameters in the marine and terrestrial realms. A series of rapid warming events, known as hyperthermals, characterise the early Eocene, followed by a long-term cooling through the middle and late Eocene. Calcareous nannoplankton, which were the dominant oceanic phytoplankton group at this time, peaked in diversity but then suffered a major decline and underwent significant population change coinciding with this major climatic reorganisation. However, the precise timing and structure of this evolutionary change is still poorly known. In this research we will produce calcareous nannoplankton assemblage records (diversity and population data) in order to determine the relationship between nannoplankton evolution and palaeoclimatic and palaeoceanographic change in the South West Pacific.