Nutrients have been amongst major observational variables in various international global ocean observation expeditions, such as the Geochemical Ocean Sections Study (GEOSECS) in the 1970s, the World Ocean Circulation Experiment (WOCE) in the 1990s, and the on-going Climate Variability and Predictability (CLIVAR). Observation of the natural variability of nutrients in the world’s oceans, and investigation of temporal and spatial changes due to the oceans’ response to climate change and increasing carbon dioxide in the atmosphere, continue to be important topics of oceanographic research. Therefore, the comparability and traceability of nutrient data in the world’s oceans are fundamental issues in marine science, particularly for studies of global climate change.

Since 1965 numerous inter-laboratory comparison studies that have been carried out to improve comparability of nutrients data in the world oceans (UNESCO, 1965, 1967; ICES 1967, 1977; Kirkwood, 1991, Aminot et al., 1995; Topping, 1997; Willie and Clancy, 2000; Clancy and Willie, 2003; Aoyama et al., 2006, 2008, 2010, 2013). However, no globally approved consensus has been achieved to date. The 4th IPCC Assessment Report in 2007 highlighted this problem inherent in comparing existing data sets: "Uncertainties in deep ocean nutrient observations may be responsible for the lack of coherence in the nutrient changes. Sources of inaccuracy include the limited number of observations and the lack of compatibility between measurements from different laboratories at different times” (Bindoff et al., 2007).

To guarantee comparability of data from different laboratories and from different research cruises, globally accepted research methods (RMs) and certified reference materials (CRMs) for nutrients' measurements are being developed and IOCCP plays an active role in these efforts. International collaboration and action is now required to harmonize oceanic nutrient data using globally accepted RMs/CRMs. Particularly important issues for the study of changes in properties of deep water masses is to develop a system by which the data within laboratories and between laboratories is comparable at the 0.1 % level. This should be both within individual cruises and extend to allowing comparison between cruises separated by decades. The IOCCP in strong collaboration with institutional and programmatic partners worldwide is going to work towards the development of such system to harmonize global oceanic nutrients analysis.