Executive Summary

The accuracy of chemical oceanographic measurements depends on calibration against reference materials to ensure comparability over time and among laboratories. Several key parameters lack reference materials for measurements in seawater, particles in the water column, and sediments. Without reference materials it is difficult to produce the reliable data sets or long-term baseline studies that are essential to verify global change and oceanic stability. This report identifies the most urgently required chemical reference materials based on key themes for oceanographic research and provides suggestions as to how they can be developed within realistic cost constraints.

Chemical analyses of seawater are uniquely difficult given the poorly known speciation and the low concentration of many of the analytes of interest. Analyses of suspended and sedimentary marine particulate materials present their own distinct challenges, primarily due to potential interference by predominant mineral phases of different types (e.g., opal, carbonate, and aluminosilicate). Of all the analytical methods applied to marine waters and particles, at present only a small fraction can be systematically evaluated via comparison to reference materials that represent the appropriate natural concentrations and matrices.

Reference materials are homogeneous, stable substances whose properties are sufficiently established as to make them useful for calibrating analytical instruments or validating measurement techniques. High-quality reference materials not only provide essential support for large-scale research studies, but also ensure accuracy of long time-series measure-



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Chemical Reference Materials: Setting the Standards for Ocean Science Executive Summary The accuracy of chemical oceanographic measurements depends on calibration against reference materials to ensure comparability over time and among laboratories. Several key parameters lack reference materials for measurements in seawater, particles in the water column, and sediments. Without reference materials it is difficult to produce the reliable data sets or long-term baseline studies that are essential to verify global change and oceanic stability. This report identifies the most urgently required chemical reference materials based on key themes for oceanographic research and provides suggestions as to how they can be developed within realistic cost constraints. Chemical analyses of seawater are uniquely difficult given the poorly known speciation and the low concentration of many of the analytes of interest. Analyses of suspended and sedimentary marine particulate materials present their own distinct challenges, primarily due to potential interference by predominant mineral phases of different types (e.g., opal, carbonate, and aluminosilicate). Of all the analytical methods applied to marine waters and particles, at present only a small fraction can be systematically evaluated via comparison to reference materials that represent the appropriate natural concentrations and matrices. Reference materials are homogeneous, stable substances whose properties are sufficiently established as to make them useful for calibrating analytical instruments or validating measurement techniques. High-quality reference materials not only provide essential support for large-scale research studies, but also ensure accuracy of long time-series measure-

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Chemical Reference Materials: Setting the Standards for Ocean Science ments. In addition, with the advent of international oceanic data collection and distribution, reference materials allow comparison of data sets from different oceanographic studies. For example, since the development and widespread use of reference materials for oceanographic measurement of dissolved inorganic and organic carbon, it is possible to achieve excellent agreement among different cruises and groups as well as different times and locations. Reference materials have provided an important mechanism for oceanographers around the world to assess data quality and improve their methods. Comparative analyses of reference materials create benchmarks for cooperative, community-wide development of improved measurement methods, without risking the stagnation that can result from requiring the use of particular standard analytical procedures. There are presently large programs in operation—and new projects being proposed—to measure chemical constituents in the ocean environment. These programs provide information on research areas such as: health and productivity of coastal oceans, sustainability of marine ecosystems, and predictability of climate change as well as other processes that affect the Earth’s population on many levels. While some of the measurements made in these programs can be calibrated against reference materials, reference materials are lacking for many others, making it impossible to compare data over time and among groups. These circumstances make the continued use of available chemical reference materials and the development of new reference materials essential. The National Research Council formed a committee in April 2001 to provide a comprehensive review of chemical reference material status and needs for those elements and compounds essential for investigating ocean processes. In addition, the committee was charged to provide advice on the elements and compounds requiring the development of reference materials and/or reference material improvement. Specifically, the committee was charged with the following tasks: compile from available sources a list of important oceanographic research questions that may benefit from chemical reference standards; create a comprehensive list of reference materials currently available for oceanographic studies; identify and prioritize the reference materials needed to study the identified research questions; determine for each priority analyte whether reference materials and/or analytic methods should be standardized; and identify the most appropriate approaches for the development and future production of reference materials for ocean sciences.

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Chemical Reference Materials: Setting the Standards for Ocean Science The Committee on Reference Materials for Ocean Science, sponsored by the National Science Foundation, held a workshop in September 2001 which brought together ocean chemists from multiple fields and agencies in the United States, Europe, and Canada to discuss the current and future needs for reference materials in ocean science. In addition, the committee surveyed the international ocean chemistry community with the aid of the American Society of Limnology and Oceanography to ascertain the community’s concerns about needed reference material development. The interactions and the input from these groups allowed the committee to prioritize the need for chemical reference materials in seawater, suspended particulate, and sediment matrices. Furthermore, the committee offered recommendations to the oceanographic community and addressed social and educational issues. Box 1 lists the committee’s recommendations for those reference materials that are needed to ensure the success of future global scale measurement programs as well as to further research in the ocean sciences on a broad number of fronts. Specific concentration information can be found in Chapter 6. A limited number of reference materials have been explicitly developed for ocean science: salinity, ocean carbon dioxide, and dissolved organic carbon. Although salinity reference materials are available on a commercial basis from Ocean Scientific International Ltd. in the United Kingdom, the others are presently supported through grants from the National Science Foundation. The widespread use of such materials and their success in enhancing the scientific return on related studies is clear, and it is essential that such materials remain available. In addition, the National Institute of Standards and Technology presently prepares a number of standard reference materials that are of immediate use to the ocean science community. These include materials for 14C (SRM 4990C) and 3H (SRM 4361C) as well as 238U, 234U, 235U (SRM 4321C), 230Th (SRM 4342— presently out of stock), 226 Ra (SRM 4969), 228Ra (SRM 4339B), 10Be (SRM 4325), ocean sediment (SRM 4357), and river sediment (SRM 4350B). Again, it is important to assure the continued availability of these materials. In addition, a variety of new materials are needed. Seawater reference materials are recommended for nutrients and for trace metals (especially iron). There is an urgent need for a certified reference material for nutrients. Completed global surveys already suffer from the lack of previously available standards, and the success of future surveys as well as the development of instruments capable of remote time-series measurements will rest on the availability and use of good nutrient reference materials. The reference materials for trace metals— though initially characterized only for the important micronutrient, iron— should ultimately be useful for the analysis of the other metals and some dissolved organic materials. The committee also recommends the devel-

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Chemical Reference Materials: Setting the Standards for Ocean Science Box 1 Recommended Reference Materials for Ocean Science Materials Recommended for Continued Availability: Currently available materials: Standard Seawater (Ocean Scientific International Ltd.) Reference Materials for Ocean CO2 (NSF via Dr. A. Dickson) Reference Materials for Dissolved Organic Carbon (NSF via Dr. D. Hansell) Various Standard Reference Materials from NIST (see text) Materials Recommended for Development: Seawater-based reference materials: One certified for the nutrient elements: nitrogen (as NO3), phosphorus (as PO4), and silicon (as Si(OH)4). One with concentrations of metals corresponding to oceanic deep water, certified for total iron concentration. One with concentrations of metals corresponding to open-ocean surface water with an information value for total iron concentration. Certified reference materials for radionuclides: An acidic solution containing 238U and 235U with daughters in secular equilibrium through 226Ra and 223Ra. An acidic solution containing 232Th with daughters in secular equilibrium through 224Ra. An acidic solution containing 210Pb with daughters in secular equilibrium through 210Po. Solid matrix-based reference materials:* Freeze-dried culture of the diatom Thalassiosira pseudonana Freeze-dried culture of the dinoflagellate Scrippsiella trochoidea Freeze-dried culture of the haptophyte Emiliania huxleyi Open-ocean, carbonate-rich sediment Open-ocean, silicate-rich sediment Open-ocean, clay mineral-rich sediment Coastal, carbonate-rich sediment Coastal, silicate-rich sediment Coastal, clay mineral-rich sediment Deltaic sediment (that has not contacted seawater) *   Each of these solid reference materials should be certified for both inorganic and organic carbon concentrations, total nitrogen concentration, δ13C of both the inorganic and the organic carbon components, and δ15N for the total nitrogen component.

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Chemical Reference Materials: Setting the Standards for Ocean Science Box 2 Additional Recommendations for Community Participation The use of appropriate reference materials should be a key feature of the quality assurance/quality control structure in any future ocean science project involving chemical measurement. Reference materials use should be explicitly addressed in the project planning stages, proposals, and publications. It is essential to develop and maintain a searchable, user-friendly database that ocean scientists can access to learn about those reference materials that are of particular interest to their research. It is essential to encourage the presentation of short courses on the best way to use reference materials to ensure quality control of analytical measurements in conjunction with national meetings for ocean scientists. It is important that round-robin exercises be organized using materials and analytes relevant to the ocean sciences and that laboratories be encouraged to participate, even at an early stage in their experience with the relevant analytical techniques. It is important that the ocean science community be encouraged to investigate the various proposed matrix-based reference materials so as to establish their properties with consensus-based values for the concentrations of a variety of constituents. Proposal and journal article reviewers need to be encouraged to question the analytical quality control of measurements made without the benefit of reference materials. opment of three primary reference solutions for radionuclides that will be useful for a variety of ocean mixing and biogeochemical studies. Particulate reference materials should be developed for three representative marine microalgae to further research on complex food webs, primary productivity, particulate fluxes, and ecological responses to climate change. The organisms proposed provide a wide-range of oceanographically relevant mineral, trace metal, and organic analytes and also represent three major marine matrices: opal, calcium carbonate, and organic matter. Furthermore, they may be used to prepare reference materials for the analysis of alkenones and photosynthetic pigments. Sediment reference materials should be developed for both open-ocean and coastal areas. Open-ocean sediments should include carbonate-rich, silicate-rich, and clay mineral-rich types. Coastal sediments should be of the same types and should include a deltaic sediment that has not been in contact with seawater. Taken together with the algal-based materials, these sediment materials would represent a wide range of diagenetic states. The committee recommends that each of these solid

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Chemical Reference Materials: Setting the Standards for Ocean Science materials (both algal- and sediment-based) be certified for both inorganic and organic carbon concentrations, total nitrogen concentration, δ13C of both the inorganic and the organic carbon components, and δ15N for the total nitrogen component. In order for the ocean community to derive maximum benefit from the proposed reference materials, the committee made several additional recommendations (Box 2). Thus, it is essential for the oceanographic community to maintain and promote the use of currently available reference materials while continuing the development of new ones. Furthermore, it is critical that the oceanographic community devotes energy to educating its members— from students and scientists to funding agencies and journal publishers— so as to ensure the quality of future chemical oceanographic observations.