Water was collected from each morning CTD and samples collected from 2 light depths equivalent to 97% and 55% of surface irradiance. This was then transferred into 2.4 l polycarbonate bottles. Each bottle was fitted with a cap with small drilled hole and teflon backed butyl rubber septa. 15N-N2 or 14N-N2 (air) was added to each bottle by injection through the septa at 1.25 ml l-1 of seawater. Following inocculation, bottles were transferred to the on-deck incubators which were maintained at surface seawater temperature and fitted with appropriate light filters. Incubations were terminated after 24 hours by filtration onto 25mm GF/F filters. The filters were placed in small Petri dishes, dried at 50°C for 12 hours, then sealed in tin capsules.
After the cruise filters were analysed for 15N and particulate nitrogen content by stable isotope mass spectrometry (PDZ-Europa 20-20) following high temperature (Dumas) combustion in an elemental analyser (PDZ-Europa GSL) in the presence of oxidation catalysts. Total nitrogen is determined from standard calibration curve using urea standards.
PDZ-Europa 20-20
Data were submitted in an Excel spreadsheet and saved to the BODC archive. The data were submitted with the following metadata: CTD cast number, date, latitude, longitude and depth of sample collection. There were no discrepancies between the data originator's metadata and the metadata held centrally in the database. Following originator's advice, the starting time of the incubation was set to 90 minutes after the end of the CTD cast.
The data were assigned parameter codes defined in BODC parameter dictionary.
Data were loaded into BODC's database using established BODC data banking procedures.
A parameter mapping table is provided below;
| Originator's Parameter | Units | Description | BODC Parameter Code | Units | Comments |
|---|---|---|---|---|---|
| PN concn | µmol l-1 | Concentration of nitrogen (total) {'PON'} per unit volume of the water body [particulate >GF/F phase] by filtration and mass spectrometry | NTOTMSP1 | µmol l-1 | - |
| Nfix | nmol l-1 day-1 | Uptake rate (daily) of dinitrogen {nitrogen fixation} per unit time per unit volume of the water body [particulate >GF/F phase] by isotope-labelled tracer addition, on-deck incubation at simulated in-situ light level, filtration and mass spectrometry | N2FIXMS1 | nmol l-1 day-1 | - |
BODC were advised by the data originator that some data from the southern hemisphere are significantly higher than expected for this area, but there is no obvious (analytical) reason to disbelieve them. Magnitude is supported by parallel measurements of acetylene reduction.
Not relevant to this data set.
| Metadata column header | Description |
|---|---|
| Cruise | Cruise ID |
| BODC_stn | Unique identifier in the BODC database for the sampling event |
| Orig_stn | Originator's name for the sampling event |
| ODV_type | ODV data type identifier |
| Gear | Type of gear for sample collection |
| Latitude[deg+veN] | Latitude of sample collection |
| Longitude[deg+veE] | Longitude of sample collection |
| W_depth[metres] | Bathymetric depth at sample collection |
| yyyy-mm-ddThh24:mi:ss[UTC] | Date and time of sample collection formatted in ISO8601 |
| Site | Hydrographic station or repeat location site name where applicable |
| Bot_depth[metres] | Depth of water sample collection in metres |
| Bot_press[db] | Pressure at water sample collection in decibars |
| BODC_bot | Unique identifier inthe BODC database for the water sample |
| Bot_Flag | Flag indicating water collection problems - see below |
| Rosette_Pos | CTD rosette position for niskin bottle samples |
| Firing_Seq | CTD niskin bottle firing sequence |
| Expt_ID | Experiment identifier |
| Expt_type | Experimental set up type |
| Expt_start_time[UTC] | Date and time of experiment start |
| Expt_duration[hours] | Experimental duration |
| Tracer | Tracers added to the experiment |
| Expt_comments | Additional information about the experiment or conditions described |
| Incubation_Depth | Targeted depth for incubation conditions |
| Light_Level[%] | The light level for the experiment as a percentage of surface irradiance |
| Incubated_volume[litres] | Incubation volume |
| Incubated_time[hours] | Duration of incubation |
| QV:BODC | Data quality flag - see below |
| Flag | Description |
|---|---|
| N/A | Unqualified |
| Below detection limit | |
| > | In excess of quoted value |
| A | Taxonomic flag for affinis (aff.) |
| B | Beginning of CTD Down/Up Cast |
| C | Taxonomic flag for confer (cf.) |
| D | Thermometric depth |
| E | End of CTD Down/Up Cast |
| G | Non-taxonomic biological characteristic uncertainty |
| H | Extrapolated value |
| I | Taxonomic flag for single species (sp.) |
| K | Improbable value - unknown quality control source |
| L | Improbable value - originator's quality control |
| M | Improbable value - BODC quality control |
| N | Null value |
| O | Improbable value - user quality control |
| P | Trace/calm |
| Q | Indeterminate |
| R | Replacement value |
| S | Estimated value |
| T | Interpolated value |
| U | Uncalibrated |
| W | Control value |
| X | Excessive difference |