TITLE. Stability of phytoplankton blooms and their role for future atmospheric CO2
PhD project of Marie Racault

SUPERVISOR & CO-SUPERVISOR(S)
Corinne Le Quéré, Erik Buitenhuis (UEA and BAS)
Trevor Platt (Bedford Institute of Oceanography, Canada)

Phd to be held either at the University of East Anglia (UEA) or at the British Antarctic Survey (BAS)

PROJECT DESCRIPTION.

The oceans absorb one quarter of the fossil fuel CO2 emitted to the atmosphere every year. Will this CO2 sink continue in the future? To answer this question, we need to understand the factors that control the transport of CO2 from the surface to the deep ocean. The sinking of organic tissues following the intense spring blooms of phytoplankton at high latitudes is one pathway by which CO2 gets drawn away from the atmopshere. At the moment, we assume that plankton blooms will continue in the future at the same intensity as today. Yet plankton blooms result from complex interactions between the surface ocean stratification, the availability of nutrients, and the rate of grazing by zooplankton.

The state of science is as follows. On the modelling side, earth system models include only basic representation of marine ecosystems. However, none of the existing ecosystem models is able to reproduce interannual variations in surface chlorophyll at high latitudes as observed by satellite. On the experimental side, iron fertilisation and mesocosm experiments have just begun to highlight the complexity of the mechanisms that trigger blooms, and of the mechanisms that control their amplitude and duration, revealing unknown processes and surprises.

This phd project would take a multi-angle approach using models and a wide variety of insitu and satellite observations to understand and quantify the importance of blooms in driving interannual variability in air-sea fluxes of CO2 and other trace gases, and to assess potential changes for the future. The approach would be to simulate iron fertilisation and mesocosm experiments in a global biogeochemistry model that includes several plankton functional types (the Dynamic Green Ocean Model) and to analyse the results in the light of the most recent observations.

The work will be undertaken in the framework of the Dynamic Green Ocean Project (http://http://www.bgc-jena.mpg.de/bgc-synthesis/projects/green_ocean), a highly dynamic and pluri-disciplinary project aimed at developing a community model of ocean biogeochemistry for applications to Earth system problems.

This Studentship will be funded by the European project carbo-ocean.