AMT15 Total Nitrogen (TN) and Total Phosphate (TP) measurements from CTD bottle samples
Originator's Protocol for Data Acquisition and Analysis
This data originates from analyses on CTD rosette bottles from 32 casts.
Water samples were collected from the five main lights depths during the pre-dawn CTD cast using the Sea-Bird CTD rosette system. Following Knap et al. (1996) samples were collected in 50-ml plastic screw-top containers and frozen at -20 o C for analysis after the cruise.
TN and TP measurements were made after unfiltered samples were irradiated for 2 hrs in 10 ml quartz glass tubes with graphite stoppers at 85 o C under high intensity UV light, without any reaction initiators, catalysts or oxidants. The UV photooxidised samples were then processed through a continuous flow autoanalyser and standard colorimetric technique applied. These techniques followed the procedures outlined in Sanders and Jickells (2000). Analysis was carried out with the equivalent samples from AMT12 and AMT14.
References Cited
Knap A., Micheals A., Close A., Ducklow, Dickson A. (eds.) 1996. Protocols for the Joint Global Ocean Flux Study (JGOFS) Core Measurements. JGOFS Report No. 19, 170pp. Reprint of the IOC Manuals and Guides No. 29, UNESCO 1994.
Sanders R. and Jickells T., 2000. Total organic nutrients in Drake Passage. Deep-Sea Research Part I, 47, 997-1014.
Instrumentation Description
Not relevant to this data set.
BODC Data Processing Procedures
Data together with the data from AMT12 and 15 were submitted to BODC in Microsoft Excel spreadsheet format on 2 occasions, with CTD cast, latitude, longitude and bottle depth to identify the samples and additional parameters for nitrate, nitrite, phosphate, DON and DOP data. The first spreadsheet referred to Total Nitrogen (TN) and Total Phosphorus (TP) and the revised spreadsheet referred to Total Dissolved Nitrogen (TDN) and Total Dissolved Phosphorus (TDP). These are 2 different measurements depending on whether the samples are unfiltered or filtered. The query was referred to the data provider who confirmed the samples were unfiltered for this cruise. Sample metadata were checked against information held in the database - there were two discrepancies. Sample metadata were checked against information held in the database - there were two discrepancies. In the data file the LAT and LON figures quoted for CTD038 related to CTD035 and CTD041 related to CTD042. Having referred to the cruise report CTD038 was the relevant pre-dawn CTD cast and has been linked accordingly. CTD041 and CTD042 were both carried out before dawn so having checked the depths in the database for each cast the depths of the samples matched CTD042.
Parameter codes defined in BODC parameter dictionary were assigned to the variables (TDN, stdevTDN, TDP and stdevTDP). The nitrate, nitrite and phosphate data were already loaded to the database as part of the nutrients dataset for this cruise and the DON and DOP provided in the original Excel files were not uploaded to the database as they were derived from the measured variables and nutrient data not directly measured. The data were assigned parameter codes defined in BODC parameter dictionary. The data were provided in units which were consistent with those used for the relevant parameters in the BODC database. Data 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 |
|---|---|---|---|---|---|
| TDN | µmol l -1 | Concentration of nitrogen (total) per unit volume of the water body [dissolved plus reactive particulate phase] by oxidation and colorimetric autoanalysis | NTOTWCTX | µmol l -1 | - |
| stdevTDN | µmol l -1 | Concentration standard deviation of nitrogen (total) per unit volume of the water body [dissolved plus reactive particulate phase] by oxidation and colorimetric autoanalysis | SDNTWCTX | µmol l -1 | - |
| TDP | µmol l -1 | Concentration of phosphorus (total) per unit volume of the water body [dissolved plus reactive particulate phase] by oxidation and colorimetric autoanalysis | TPHSPP01 | µmol l -1 | - |
| stdevTDP | µmol l -1 | Concentration standard deviation of phosphorus (total) per unit volume of the water body [dissolved plus reactive particulate phase] by oxidation and colorimetric autoanalysis | SDTPHP01 | µmol l -1 | - |
Data Quality Report
The dataset has been checked by the data originator - any suspect data values were flagged in the dataset before submission to BODC and have been loaded with BODC flag 'L'.
Problem Report
Not relevant to this data set.
