Studying the marine biogeochemistry of Isoprene (C5H8) through remote sensing images and ecological modelling

2018 edition

Pablo Rodriguez-Ros

The behaviour of atmospheric particles, when acting as aerosols, is one of the biggest uncertainty sources in global warming projections. This is because they have the ability of strongly influence the formation and the optical properties of clouds; consequently, they could affect the planetary energy balance. In the recent years, there have been very significant advances in numerical modelling of the atmosphere and its processes, including aerosols formation and behaviour. However, the global climate implications of aerosol-cloud processes are still very difficult to predict, in part due to an incomplete knowledge about inputs and sources of aerosols. In the pristine marine atmosphere, where cloud formation processes are highly susceptible to aerosol emission, an important part of particle formation occurs from the oxidation of trace gasses exhaled from sea. Isoprene (C5H8), a precursor of secondary organic aerosol, is a trace gas produced eminently by marine photosyntetic organisms. Therefore, it is possible to infer its concentration in the surface ocean using chlorophyll-a concentration as a proxy. The antarctic ocean is an outstanding area to study the biological production of trace gasses, and its influence in the lower atmosphere. We have recompilate seasurface concentration data of isoprene, and other environmental and ecosystemic variables, from two different oceanographic cruises: “PEGASO” (Weddell Sea, Oarkney Islands & South Georgia Islands) and “ACE Expedition” (complete circumnavigation of the Southern Ocean). In this work we present the relationship between isoprene concentration and chlorophyll-a values obtainned from in situ measurements and from remote sensing products (MODIS aqua) along the Southern Ocean. We also tested previously developed numerical algorithms and compared them with our results in order to improve their accuracy and predictability. Recent studies have also demonstrated that it is possible to quantify not only the biomass but also the phytoplankton community composition using remote sensing data of chlorophyll-a to determine PFTs. Thus, we tested their ability to determine the relative contribution of every PFT to the total isoprene production.