Ocean colouring data sheds lights on carbon cycle
Work done within the European Space Agency's GlobColour project now contributes significantly to ocean carbon cycle research. ESA merged 55 terabytes of data to produce a ten-year dataset of global ocean colour stretching to 2007, providing information on how marine biological activity and man-made carbon dioxide emissions are interlinked. The colour of ocean water is largely determined by phytoplankton, microscopically small marine plants that live in the well-lit surface layer of the ocean. While most individual phytoplankton are too small to be visible to the naked eye, the chlorophyll they contain will tint the seawater depending on the number of plankton present. The chlorophyll also means that - just like plants on land - phytoplankton absorb the greenhouse gas carbon dioxide (CO2) during photosynthesis and store it in their tissues, so that they potentially play a considerable role as carbon sinks. The colouring caused by the phytoplankton can be picked up from space. In the framework of GlobColour, the ESA researchers made use of three different instruments aboard different satellites: the Medium Resolution Imaging Spectrometer (MERIS) aboard the Envisat platform, the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA's Aqua satellite and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) on GeoEye's Orbview-2. According to ESA, the GlobColour project provides better sampling and reduced instrumental bias by comparison with existing systems, as it combines observations from multiple sensors. Comparing the data with measurements from in-situ buoys has also shown that the error margin is smaller when the data from the different sensors are merged. 'I am quite impressed by the work ESA has done so far within GlobColour,' says Dr Cyril Moulin of the International Ocean Carbon Coordination Project (IOCCP). 'This ten-year dataset is going to be very useful for carbon studies and global modelling.' In addition, the researchers are confident that the data will benefit the fisheries and aquaculture industries. 'We need to sustain an international effort to make sure we can link one satellite dataset to another to build the long-time series that we need to distinguish change from cycles, and GlobColour is definitely a significant step in that perspective,' adds Dr James Yoder, chair of the IOCCP. The datasets are publically available via the GlobColour website, which has a new web interface that allows users to narrow down the time period, spatial region and product type. Near-real time observations are expected to start in mid-2008. As of 2009, the service will continue as part of the Marine Core Service of the GMES (Global Monitoring for Environment and Security) initiative, a joint initiative of the European Commission and ESA.