PhD: Plankton Dynamics in the Iceland Basin and Greenland Margin

Phytoplankton – single cellular organisms that photosynthesise in the surface ocean – are the base of the open ocean marine food chain. In the mid-to-high latitude oceans phytoplankton growth is often dominated by rapid cell growth over a large area through spring and early summer, so called phytoplankton ‘blooms’. Although these blooms consist of single celled organisms, they reach such abundances as to be observable from space (Figure 1). This rapid growth of phytoplankton cells, with their uptake of carbon from the oceans by photosynthesis, plays a major role in both the ocean carbon cycle and marine food chains.

This project will focus on a dominant group of marine eukaryotic phytoplankton, the coccolithophores, that are unusual in producing a calcium carbonate external cell covering (coccoliths). The production of a biomineral makes them even more significant in terms of carbon cycling, but also allows for changes in bloom dynamics to be traced back through time using the sedimentary record of coccoliths. This record reveals an intriguing pattern of alternating dominance between two major groups of coccolithophores during different recent warm “inter-glacial” climate stages. The cause of these variations are poorly understood, even though they are important for ecoysystems and the carbon cycle because one group is relatively large and heavily calcified (Coccolithus pelagicus) whilst the other is relatively small and lightly calcified (Gephyrocapsa species). Both groups live in the modern North Atlantic and their changing abundance and species ranges with climate change is an important component of the future open ocean ecosystem dynamics.

The project aims to combine understandings of modern physiology, with climate modelling and reconstructions of coccolithophore assemblages through recent inter-glacial climates to understand the temperature, nutrient and salinity controls on the dynamics species dominance. With this understanding, the student will contribute to improving modern ecosystem models that include coccolithophore functional groups and are being used in the prediction of future ecosystem change.