Roughly 70% of the Earth’s surface is covered by ocean. About half of the global primary production (photosynthesis) occurs in the ocean. Most of the primary producers in the ocean comprise microscopic plants and some bacteria; these photosynthetic organisms called phytoplankton form the base of the ocean’s food web. Changes in phytoplankton biomass would have major implications for the ocean’s ability to take up atmospheric CO2 and support current rates of fish production, as well as the overall health of the ocean, which is currently threatened by multiple stresses such as increased temperature and ocean acidification (both due to anthropogenic CO2 emissions), marine pollution, and overfishing.
Marine Food Web
The conversion of carbon dioxide and water into carbohydrates and oxygen in the presence of light represents the energy supply to single-celled organisms (for example, phytoplankton), the base of marine food webs. Ocean color measurements are used to learn about the composition of phytoplankton, microscopic organisms that live in the sunlit, or photic, zone of the ocean and create energy through photosynthesis. These organisms make up half of all photosynthetic activity on the planet and provide half of the oxygen in the Earth’s atmosphere.
Source: NASA Goddard Multimedia
Source: NASA Earth Observatory
Ships alone cannot collect observations rapidly enough to provide a global synoptic view of phytoplankton abundance, so in 1978 the first ocean color satellite was launched and has made it possible to obtain a global view of the oceans’ phytoplankton biomass in the form of chlorophyll. The satellite observations led to improved insight of global ocean primary production, as well as better understanding of climate change and the processes affecting how biomass and productivity change within the ocean basins daily. Ocean color measurements reveal a wealth of ecologically important characteristics that many scientists and operational users rely on for research, ecosystem monitoring, and resource management. These characteristics include:
- chlorophyll concentration (a proxy for the biomass of marine plants or phytoplankton)
- the rate of phytoplankton photosynthesis
- sediment transport
- dispersion of pollutants
- responses of oceanic biota to long-term climate changes (IOCCG, 2008).
In addition, related parameters derived from ocean color satellites can be used to monitor oil spills, harmful algal blooms, and the health of important fisheries’ habitat.
International Ocean Colour Coordinating Group (IOCCG). 2008. IOCCG Report Number 7: Why ocean colour? The societal benefits of ocean-colour technology. In: Reports and Monographs of the International Ocean-Colour Coordinating Group. Platt, T., N. Hoepffner, V. Stuart, and C. Brown (Eds.). IOCCG, Dartmouth, Nova Scotia, Canada.