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CD176 Discrete Dissolved Inorganic Nutrients Sampling Document

Originator's Protocol for Data Acquisition and Analysis

Water samples were collected from CTD stations throughout the cruise for the analysis of dissolved inorganic nutrients using an onboard Lachet Quickchem 8000 colorimetric flow injection autoanalyser. Shortly after the cruise started a fault developed with the autosampler, which prevented further onboard analysis. Subsequent samples were collected and filtered through GF/F 0.7 µm filters, before being frozen for analysis back at SAMS.

References Cited

Sherwin, T. A. et al , (2005) 'Cruise CD176 Birkenhead to Falmouth via Rockall, Iceland and Oban', Internal Report No 248, Scottish Association for Marine Science.

Available - Cruise CD176 Internal Report

BODC Data Processing Procedures

The nutrient data were supplied to BODC in Microsoft Excel spreadsheets. Values were extracted from these and loaded into BODC's ocean database under an ORACLE Relational Database Management System. Data that were considered unrealistic were flagged suspect.

Several inconsistencies were noted between the cruise report CTD logsheets and the originator spreadsheets relating to particular Niskin bottles sampled. In all cases the uncertainty involves multiple bottles fired at the same depth, so assignment to bottle numbers was deemed somewhat arbitrary.

Data listed out from the BODC database are done so at a resolution deemed appropriate for that particular variable and the analytical procedure involved. In some instances this results in the listing out of zero values.

SAMS nitrate data quality warning

SAMS have notified BODC of a problem in the analytical procedure adopted for nitrate analysis on this cruise. The problem relates to the technique used to prepare the analytical standards, which results in nitrate (and consequently nitrite) values which are typically 10-15 % higher than they should be. Absolute data values should therefore be used with extreme caution.

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