5.1 Assessing Requirements for Sustained Ocean Color
Research and Operations

A Report of the OSB and SSB Ad Hoc Committee on Assessing Requirements for
Sustained Ocean Color Research and Operations

Summary

The ocean hosts a fundamental component of Earth’s biosphere. Marine organisms play a pivotal role in the cycling of life’s building blocks such as nitrogen, carbon, oxygen, silica, and sulfur. About half of the global primary production—the process by which CO2 is taken up by plants and converted to new organic matter by photosynthesis—occurs in the ocean. Most of the primary producers in the ocean comprise microscopic plants and some bacteria; these photosynthetic organisms (phytoplankton) form the base of the ocean’s food web. Scientists are exploring how future climate change and sea surface warming might impact the overall abundance of phytoplankton. A long-term change in phytoplankton biomass would have major implications for the ocean’s ability to take up atmospheric CO2 and support current rates of fish production. Therefore, sustaining a global record of the abundance of phytoplankton and their contribution to global primary productivity is required to assess 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.

Because the ocean covers roughly 70 percent of Earth’s surface, ships alone cannot collect observations rapidly enough to provide a global synoptic view of phytoplankton abundance. Only since the launch of the first ocean color satellite (the Coastal Zone Color Scanner [CZCS] in 1978) has it been possible to obtain a global view of the ocean’s phytoplankton biomass in the form of chlorophyll. These observations led to improved calculations of global ocean primary production, as well as better understanding of the processes affecting how biomass and productivity change within the ocean basins at daily to interannual time scales.

THE OCEAN COLOR TIME-SERIES IS AT RISK

Currently, the continuous ocean color data record collected by satellites since the launch of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS, in 1997) and the Moderate Resolution Imaging Spectroradiometer (MODIS, on Terra in 1999 and on Aqua in 2002) is at risk. The demise of SeaWiFS in December 2010 has accentuated this risk. MODIS on Aqua is currently the only U.S. sensor in orbit that meets all requirements (see below) for sustaining the climate-quality1 ocean color time-series and products. However, this sensor is also many years beyond its design life. Furthermore, it is no longer possible to rectify problems with the Aqua sensor degradation that were addressed through comparisons with SeaWiFS in the past few years. Therefore, it is uncertain how much longer data from U.S. sensors will be available to support climate research. Although the European Medium-Resolution Imaging Spectrometer (MERIS) meets all the requirements of a successful mission, it is also beyond its design life. Because of the many uncertainties surrounding the next U.S. satellite mission (more specifically the Visible Infrared Imager Radiometer Suite [VIIRS] sensor scheduled to launch fall 2011); data acquired through the VIIRS mission threaten to be of insufficient quality to continue the climate-quality time-series.

Even if fully successful, the VIIRS sensor’s capabilities are too limited to explore the full potential of ocean col- or remote sensing. Thus, the U.S. research community is looking to National Aeronautics and Space Administration (NASA) to provide ocean color sensors with advanced capabilities to support new applications and for significant improvements to current research products beyond what is possible with data from SeaWiFS and MODIS or will

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NOTE: “Summary” reprinted from Assessing Requirements for Sustained Ocean Color Research and Operations, The National Academies Press, Washington, D.C., 2011, pp. 1-7.

1 Climate-quality observations are a time-series of measurements of sufficient length, consistency, and continuity to assess climate variability and change (following NRC, 2004b).



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