A Centuries-long History of Participatory Science in Optical Oceanography: from observation to interpretation of natural water colouring.

Participatory science is not, as perhaps is believed, something of the 21st century. In this manuscript we show that over a century ago it were not only scientists who collected oceanographic data but also merchant sailors. A good example of such globally collected data are Forel-Ule observations, from which the first date back to 1889. This hardly explored (NOAA) dataset, containing around 228,000 of so-called ocean colour observations, was recently analysed on trends. Some of the material here presented refers to a recent publication ‘Trends in Ocean Colour and Chlorophyll Concentration from 1889 to 2000, Worldwide’ (Wernand et al., 2013). Since the launch of satellite-mounted sensors globe-wide monitoring of chlorophyll, a phytoplankton biomass proxy, became feasible. Just as satellites, the Forel-Ule (FU) scale record (a hardly explored database of ocean colour) has covered all seas and oceans - but already since 1889. We provided evidence of the usefulness of the Forel-Ule scale observation record dating back to 1889 from which changes of ocean surface chlorophyll can be reconstructed with confidence from this record. Our analysis has not revealed a globe-wide trend of increase or decrease in chlorophyll concentration during the past century; ocean regions have apparently responded differentially to changes in meteorological, hydrological and biological conditions at the surface related to global warming. Since 1889 chlorophyll concentrations have decreased in the Indian Ocean and in the Pacific; and increased in the Atlantic Ocean, the Mediterranean, the Chinese Sea, and in the seas west and north-west of Japan. Clearly, explanations of chlorophyll changes over long periods should focus on hydrographical and biological characteristics typical of single ocean regions, not on those of ‘the’ ocean. To facilitate climate change research we recommend the reintroduction and use of the Forel-Ule scale to expand the historic database. Accordingly, through participatory science, with the help of the public, we like to establish this goal. We suggest the manufacturing and distribution of a new type, easy to make, Forel-Ule scale, recently developed within the EU-project „Citizens’ Observatory for Coast and Ocean Optical Monitoring“ (Citclops). Additionally, within the same project a smartphone App is being developed to facilitate public involvement in worldwide collection of Forel-Ule data.