The following discussion and recommendations were made during the workshop on QA/QC of chemical oceanographic data in February 2010. Official guidelines for specific chemical compounds e.g. ocean acidification data and nutrient data have been published since (see links in Data reporting and exchange sections) and the guidelines they contain should be read in conjunction with our recommendations. Comments are invited via the "Comment" box below.

1     Can we recommend an existing best practice document for data reporting and exchange?

While informal recommendations and guidelines for submitting data do exist in a number of data centers, the group was not aware of the existence of a best practice document dealing specifically with oceanographic chemical data reporting and exchange.

Proposal: the meeting agreed that there is no existing document and that one should be developed.

Meanwhile, it is recommended that at a minimum, the following information be provided in data report prepared by data originators when the data are submitted to the data centers:

• sample preservation/handling/transport protocol (after sampling but before analysis);
• analytical method specification with reference (e.g. published, citable reference used or deviations from reference cited), specifying procedure, equipment, precision, accuracy, method detection limit, significant figures as determined by the measurement precision;
• sampling and sample preparation including filtration,  preservation and analysis;
• Certified Reference Material (CRM), or standard availability and use;
• estimation of measurement uncertainty;
• inter-laboratory comparison study availability;
• laboratory analysis duplicate limits (repeatability of analysis);
• use of internal QC with specified precision limits.
  

If the laboratory is accredited then this should be specified.

2     Can we agree on a common reporting terminology and unit for each variable?

Data submitted to data centres use non standard and sometimes inaccurate or ambiguous terminology to label chemical parameters and units.

With regards to parameter names:

Proposal: the meeting recommended the following terminology for dissolved inorganic nutrients and dissolved oxygen in seawater:

• Recommended term: SILICATE [Silicic acid is the dominant form of reactive silicate in seawater (e.g., Gordon et al., 1993; Isshiki et al., 1991)]
• Recommended term: NITRATE+NITRITE should be reported if this is what was measured.
• Recommended term: NITRATE (specify whether it was measured directly or if reported as subtracted from measurements of NITRATE+NITRITE minus NITRITE; if the latter then NITRITE should also be reported)
• Recommended term: NITRITE
• Recommended term: PHOSPHATE
• Recommended term: OXYGEN
• Recommended term: AMMONIUM

For accuracy, abbreviations of measured variables and concentration units should be spelled out completely as part of the metadata.

The issue of units usage and conversion was then discussed in depth. Units should follow the international standards and be as close to the measurement unit as possible.

Proposal: it was recommended to use units of micromole per liter (μmol / l)  which complies with the SI recommendation (NIST Special Publication 330, 2008) for both dissolved nutrients and dissolved oxygen.

However while the group agreed that concentrations should be reported on a mole per volume basis, it was recognized that a large part of the oceanographic community required concentration of substance in sea water to be reported in units of moles per kilogram.

It is therefore recommended that data producers provide sufficient information to enable values to be converted to/from per volume/per mass for both nutrient and oxygen data. The meeting recognized the difficulty in the conversion between per volume and per mass units, for the reason that the exact temperature and salinity which were used (for the conversion) are not always reported. In order to do an accurate conversion from units of moles per mass to units of moles per volume, the originator of the data needs to provide at a minimum the seawater density conversion factor and the equation of state used in the conversion. In order to convert units of moles per volume into units of moles per mass the originator needs to provide the appropriate temperature, which is, for nutrients, laboratory temperature at the time the sample was analyzed, and for oxygen, water temperature at the sample was drawn.

As a conclusion the group recommended that:

• if submitting data in units per mass, originators supply sufficient information to enable future conversion from per mass to per volume units (and vice versa) to be done accurately. At a minimum this requires the density conversion factor, the equation of state and the temperature used in the calculation of the density;

• if submitting data in units per volume, originators should also supply the temperature of oxygen sample fixation if measured or, for nutrients, the temperature of the analysed sample (i.e. laboratory temperature), and in situ salinity if not already held at the data center.