Paleogene to early Neogene calcareous nannoplankton biochronology and evolution (IODP Expedition 390/393)

Lead Research Organisation: University College London
Department Name: Earth Sciences

Abstract

Calcareous nannoplankton are microscopic marine algae that produce calcite exoskeletons (coccospheres/coccoliths) which can be found in almost all marine sediments in the geological record. By studying the calcareous nannofossils preserved within sediments cored from the sea-floor by the International Ocean Discovery Program (IODP) we can document their evolution through time, including changing number of species (diversity), rates of speciation and extinction, and population compositions. We can use this information to provide accurate ages of the sediments, which is an important task on a deep-sea drilling ship like the IODP JOIDES Resolution, and these results will tell us whether we have achieved our initial objectives. Calcareous nannoplankton are sensitive to changes in ocean environment, particularly sea-surface temperature and nutrient availability, with individual species or groups preferring specific ecological niches. Using the abundance of fossil species, we are able to reconstruct past environmental conditions for a specific location at a given time. IODP Expedition 390 will sail to the South Atlantic Ocean and core deep-sea sediments from the Paleogene to Neogene time interval (around 60 million years ago to present), a key interval in Earth's climate history marking the transition from high CO2, very warm 'greenhouse' climates into a much cooler 'icehouse' world with large Antarctic ice sheets that waxed and waned. This profound interval of climatic change saw dramatic shifts in the environments and ecosystems of the marine and terrestrial realms. A series of rapid warming events, known as hyperthermals, characterise the early Eocene (~56-50 million years ago), followed by long-term cooling through the later Eocene, and then glacial-interglacial cycles through the Oligocene and early Miocene (~33-20 million years ago). Calcareous nannoplankton were the dominant ocean phytoplankton at this time and peaked in diversity in the Eocene but then suffered major decline coinciding with this major climatic change from greenhouse to icehouse. However, the precise timing and speed of this evolutionary change is still poorly known and we plan to better understand this relationship between plankton evolution and palaeoclimatic change in the South Atlantic. A better understanding of this relationship is key to predicting the magnitude and impact of future climate change on the ocean biosphere and ecosystem functions. To answer these research questions, we first have to check that the deep-sea cores that we will drill will be of the right geological age, with continuous records through time, and in sediment types that preserve the fossils we need. This research project will provide the age control for the sites that were drilled by the preliminary IODP Expeditions 390C and 395E and this will be key to the success of the forthcoming expeditions which will sail in 2022.

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