Abstract
Oceanographic data from 28 cruises performed in the NW Mediterranean Sea between 1982 and 2003 and data from historical databases, amounting to more than 100000 data points, are used to define the quality control ranges at standard level depths of dissolved inorganic nutrients, dissolved oxygen and chlorophyll a . The quality of each of the key variables and the analytical precision are assessed. The results indicate that freezing is a valid preservation method for phosphate, nitrate, silicate and nitrite in samples from the NW Mediterranean Sea, though their relative error increases (6.3%, –1.6%, –2.5% and –11.4%, respectively). In contrast, freezing nutrient samples on the cruises gathered negatively affected the analytical precision and accuracy of the ammonium analysis. The analysis precision is also estimated using different approximations, the most realistic being the use of replicate samples from the same sampling bottle. Except for phosphate and dissolved oxygen, specific quality control ranges for mixed water columns, usually found in winter, have to be defined, since the surface concentrations are particularly high due to deep water mixing. The quality-controls described in this work are an important and useful tool for validating data and for detecting erroneous or anomalous data obtained in both historical and future works in the NW Mediterranean Sea.
Highlights
Oceanographic databases are basic tools for preserving historical observations and for describing and tracking changes in ecosystems
SUMMARY: Oceanographic data from 28 cruises performed in the NW Mediterranean Sea between 1982 and 2003 and data from historical databases, amounting to more than 100000 data points, are used to define the quality control ranges at standard level depths of dissolved inorganic nutrients, dissolved oxygen and chlorophyll a
The results indicate that freezing is a valid preservation method for phosphate, nitrate, silicate and nitrite in samples from the NW Mediterranean Sea, though their relative error increases (6.3%, –1.6%, –2.5% and –11.4%, respectively)
Summary
Oceanographic databases are basic tools for preserving historical observations and for describing and tracking changes in ecosystems. Researchers constructing databases that include decades of oceanographic research should take into account that most probably there are very significant differences in the way the measurements were obtained. Such differences include changes in the analysis instruments, the sampling and the preservation procedures. It is necessary to check whether data collected and processed using different methodologies and precisions can be combined. Since nowadays so much research is used to try to determine climate change or anthropogenic impacts, basic information about the analysis precision, limit of detection and other analytical characteristics is critical
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