PHYCASO - Phytoplankton evolution and carbonate dynamics during past regimes in the Southern Ocean (IODP Expedition 392)

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Given the threat of a sixth mass extinction event as a result of human-based climate breakdown and habitat disruption, implications about the long-term outlook of marine species and ecosystems are now of paramount importance. Coccolithophores (also known as calcareous nannoplankton) are an abundant group of eukaryotic unicellular phytoplankton that are widespread in the sunlit upper oceans and represent the base of the food chain in marine ecosystems. These miniscule organisms precipitate a multitude of elaborately shaped scales of calcium carbonate (coccoliths- composed of bonded calcium and carbon) to form a protective armour known as a coccosphere. When these microscopic plankton die, their skeletons begin to fall to the ocean floor forming carbon-rich sediments and populating the fossil record. Studying the preserved communities of fossil coccolithophores, we can understand the evolution and diversity of marine life through time and reconstruct past environmental conditions that played out to predict how modern communities will respond to ongoing and future climatic changes. International Ocean Discovery Program Expedition 392 will drill deep-sea sediments in the Agulhas Plateau, Southern Ocean that span Cretaceous to early Quaternary time, a key interval in Earth's history that represents a long-term transition from warm and high CO2 states into much cooler 'icehouse' worlds with large Antarctic ice sheets. These are related to perturbations similar to the present-day global warming, but the precise impact on the oceanic primary production and carbonate development still remains elusive. In this research, we aim to produce records of diversity, evolutionary morphological change, and accumulation rate and compare these with pCO2 proxies of geologically abundant coccolith species to determine the relationship between coccolithophore (plankton) evolution and pelagic primary carbonate production with the palaeoclimate in the Southern Ocean. An understanding of this relationship is key to predicting the impact of climate change on the functionality of the present-day oceanic ecosystems.