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GCOS Ocean Sub-Surface ECV Definition: Nutrients - Though small in concentration compared to seawater's major constituents, nutrients, primarily nitrate (N) and phosphate (P), are extremely important to the biology of the oceans. In some cases, iron (Fe) and silica (Si) may also act as limiting nutrients. The ratio of the concentration of carbon to nitrate to phosphate in phytoplankton is 106:16:1, which are the classic "Redfield Ratios". Chemical and biological oceanographers frequently analyze nutrient data with respect to the Redfield Ratios to determine which nutrient is the production-limiting nutrient. While Fe is important in some regions, particularly open ocean regions distant from land, in most productive regions the limiting nutrient is either N or P. (N and P are actually present as dissolved nitrate ion and dissolved phosphate ion, but N and P are used for convenience.) (from the NASA/GFSC Ocean Color web site) Introduction: Systematic sampling of the global ocean is needed to fully characterise oceanic climate variability. Global implementation of upper-ocean measurements in ice-free regions is technically feasible, with proven techniques, but remains to be accomplished. This will be addressed initially through the implementation of the agreed upper-ocean network, the in situ component of which initially requires 3000 Argo profiling floats, about 40 repeat XBT lines, 30-40 surface reference moorings, and about 120 tropical moorings, together with high-precision satellite altimetry. Similar to the surface, the Global Reference Mooring Network will provide essential reference-quality long-time records of sub-surface variables to identify climate trends and climate change. They also provide critical platforms for the testing and pilot project use of technology for autonomous measurement of biogeochemical and other ecosystem variables. The records from the Global Reference Mooring Network also will be important for testing climate models and their parameterizations. As new technologies are proven, as our understanding of the sampling requirements improves, and as our ocean analysis and reanalysis capabilities are exploited, the recommended global sub-surface observing system will evolve. WCRP will encourage the development of ocean climate reanalyses, including all appropriate historical data assimilated into ocean models, to create climate variability and trend analyses, and to support seasonal-interannual to decadal climate prediction. They will also encourage other efforts to develop analyses and reliable datasets and products of climate variability and trends. Sub-surface Nutrients (phosphate, nitrate, silicates, silicic acid): Nutrient data are essential biogeochemical information, and provide essential links between physical climate variability and ecosystem variability, but are not adequately observed. They give an additional perspective on ocean mixing.
These networks are research and/or pilot programmes and require technology development to attain reliable and accurate autonomous sensors and to deploy observing systems to sample better sub-surface nutrient variability. Additional Information:
References:
Data, Product, Metadata and Information Access [ECV Matrix Main Page] [About the ECV Matrix] [Reference Documents] [Contact] [Updated February 25, 2011]
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