D365 RRS Discovery Cruise discrete inorganic nutrients sampling document
Cruise details
| Dates | 2011-05-11 - 2011-06-02 |
|---|---|
| Principal Scientific Officer | Jane Read (National Oceanography Centre, Southampton) |
| Data Originator | Estelle Dumont (Scottish Association for Marine Science) |
The Extended Ellett Line is a full-depth hydrographic section between Iceland, 60°N 20°W, Rockall and Scotland. The original Ellett Line across the Rockall Trough was first occupied in 1975 when measurements were attempted four times a year. In 1996 the line was extended to Iceland and since then has been occupied approximately annually. The data form a 35 year time series of the oceanic conditions west of the British Isles. The section monitors the characteristics of the warm water inflow into the Nordic Seas and thence to the Arctic, and observes part of the returning cold water outflow with measurements of the Iceland-Scotland Overflow and the overflow of the Wyville-Thomson Ridge into the Rockall Trough. In total 55 CTD casts were completed during the cruise along the original and Extended Ellett Line, with nutrient samples being taken from the majority of bottles fired on the upcasts.
Originator's data acquisition and processing
The basic water column dissolved nutrients, ammonia, phosphate, silicate (reactive silica) and total oxidized nitrogen (nitrite + nitrate) were analyzed from CTD casts along the Extended Ellett Line. CTD depths for the samples were chosen to correspond with those of the chlorophyll and algal cell count studies down to 200 m and at depths below this corresponding with CFC gas studies. Additional other depths were sometimes chosen to coincide with changes in water mass identified by the TS and dissolved oxygen characteristics from the CTD casts.
Samples were collected in 125 ml acid cleaned polythene bottles directly from the CTD spigots without the use of a tube. Samples were always analyzed within 24 hours of collection and stored in a fridge prior to analysis. Measurement was conducted using a Lachat QuikChem 8500 flow injection autoanalyser using the manufacturers recommended methods: Ammonia, 31-107-06-1-B; Orthophosphate, 31-115-01-1-G; Silicate, 31-114-27-1-A and Nitrate/Nitrite, 31-107-04-1-A.
Samples were measured in triplicate to identify instrument precision. Standards were prepared in deionised water and the samples and standards run in a carrier stream of deionised water. A standard reference solution prepared from nutrient standard solutions supplied by OSIL containing 1µMNH4, 1µMPO4, 10µMSiO2 and 10µMNO3 was run at the start and end of each sample batch to determine analytical accuracy and to adjust for calibration drift during the course of a sample batch analysis.
BODC data processing procedures
Data arrived at BODC in a Microsoft Excel spreadsheet containing 1109 nutrient samples taken during the cruise. The spreadsheet was initially converted into a Comma Separated Values format file ( .csv ) and appropriate BODC parameter codes were subsequently assigned. The following table shows how the variables supplied were mapped to BODC parameter codes.
Please note: 1109 CTD OTE bottles were fired during 55 CTD casts taken on cruise D365. However, not all of these bottle firings resulted in nutrient samples being taken and/or analysed to produce valid measurements.
Content of data series
| Originator's Parameter | Originator's Units | Parameter description | BODC Parameter code | BODC Units | Comments |
|---|---|---|---|---|---|
| Nitrate | µM | Concentration of nitrate+nitrite {NO3+NO2} per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis | NTRZAATX | µmol l -1 | Nitrate=nitrate+nitrite |
| Silicate | µM | Concentration of silicate {SiO4} per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis | SLCAAATX | µmol l -1 | |
| Phosphate | µM | Concentration of phosphate {PO4} per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis | PHOSAATX | µmol l -1 | |
| Ammonia | µM | Concentration of ammonium {NH4} per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis | AMONAATX | µmol l -1 |
The data were loaded from the .csv file into an Oracle database where measurements were linked to corresponding depths through the CTD rosette bottle no. (supplied by the originator) and the CTD rosette bottle no. obtained from electronic Seabird CTD logs (which contained accurate pressure readings for each bottle fired).
Data that lay outside the permitted range for the parameter code were flagged suspect with an 'M' flag by BODC.
Data Quality Report
No problems reported and no significant issues encountered during BODC banking procedures.
Problem Report
No problems reported and no significant issues encountered during BODC banking procedures.
References
Further information can be found in the cruise report cruise report
