In order to understand the marine phytoplankton’s role in the global marine ecosystem and biogeochemical cycles it is necessary to derive global information on the distribution of its biomass and primary production, in particular the distribution of major functional phytoplankton types (PFT) in the world oceans. Using common ocean color sensors like SeaWiFS or MERIS, only overall the phytoplankton biomass or the dominant phytoplankton group can be derived. In order to get a global quantitative estimate of different PFT in the oceans, we adapted the technique of Differential Optical Absorption Spectroscopy (DOAS), which has been established for retrieval of atmospheric components, for the retrieval of the absorption and biomass of two major phytoplankton groups (PhytoDOAS) from data of the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) satellite sensor. SCIAMACHY measures back scattered solar radiation in the UV-Vis-NIR spectral regions with a high spectral resolution (0.2 to 1.5 nm). In order to identify phytoplankton absorption characteristics in SCIAMACHY data in the range of 430 to 500 nm, phytoplankton absorption spectra measured in-situ during two different RV Polarstern expeditions were used. The two spectra have been measured in different ocean regions where different phytoplankton groups (cyanobacteria and diatoms) dominated the phytoplankton composition. Results show clearly distinct absorption characteristics of the two phytoplankton groups in the SCIAMACHY spectra (see Fig. 1).

Using these results in addition to calculations of the light penetration depth derived from DOAS retrievals of the inelastic scattering (developed by Vountas et al., 2007), globally distributed pigment concentrations for these characteristic phytoplankton groups for two monthly periods (Feb-Mar 2004 and Oct-Nov 2005) were determined (see Fig. 2). This satellite information on cyanobacteria and diatoms distribution matches well the concentrations based on high pressure liquid chromatography (HPLC) pigment analysis of collocated water samples and concentrations derived from a global model analysis with the NASA Ocean Biogeochemical Model (NOBM; details in Gregg et al., 2003, Gregg and Casey 2007). The quantitative assessment of the distribution of key phytoplankton groups from space enables various biogeochemical provinces to be distinguished and will be of great importance for the global modeling of marine ecosystem and biogeochemical cycles which enables the impact of climate change in the oceanic biosphere to be estimated. More details about this study you can find in Bracher et al. (2009).