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On RV Callista, collection was done through the use of Niskin bottles mounted on a CTD which were fired at different depths. This allowed for samples that would illustrate any trends or patterns throughout the water column. Samples were then filtered in the wet lab onboard and processed for later analysis in the lab. In the lab, samples were once again processed to analyze their concentrations. Nitrate values were then analyzed using a spectrometer.

Upon analysis of nitrogen concentrations from stations 28, 29, and 32, trends for each of the three stations could be compared. Nitrate concentrations at stations 28 and 29 remained fairly constant with increasing depth while station 32 exhibited different behaviour. The outlier at station 32 could deviate harshly due to temporary temperature or salinity fronts that existed within the water column.

Upon analysis of phosphate concentrations from stations 28, 28, and 32 trends or relationships in the data could be analysed and compared. Stations 29 and 32 both exhibit a decrease in phosphate concentration while station 28 appears to decrease until a depth of 30 meters where it then begins to increase again. Like the nitrate concentration data, this could be due to salinity or temperature fronts at differing depths.

Figure 3.5. Nitrate concentrations in µg/L against depth in meters for stations 28, 29, and 32. There is one outlier present for station 32 with a nitrate concentration of 2.36 µg/L and a depth of 23.5 m.

Figure 3.6. Phosphate concentration in µg/L against depth in meters for stations 28, 29, and 32.

Chemistry

Nitrate

Phosphate

At all three stations, the concentration of silicon increased below the depth of 20. An increase in silicon concentration was observed at all depths at station 28 where Niskin bottles were fired and samples were taken. Both stations 29 and 32 displayed a slight initial decrease in concentration before an increasing below 20m. Station 29 exhibited the largest decrease in silicon at depths above 20m: the concentration of silicon decrease by 0.02µmol/L between 10.4m to 20.1m.

The observed increase in silicon below 20 metres might indicate the bottom of the surface layer, that is to say the seasonal thermocline. Due to restricted mixing between the two layers, remineralisation below the thermocline exceeds the uptake of silicon by phytoplankton. This results in an increase in silicon below the thermocline.

Silicon

Figure 3.7. Silicon concentration in µmol/L against depth in meters for stations 28, 29, and 32.

Figure 3.8 shows that oxygen spikes at an approximate depth of 9-11m at stations 46, 48 and 52; this can be seen by the fact that at station 52, the highest oxygen saturation occurred at a depth of 9.3m with a value of 87%. In addition, this trend is also supported by station 48, where at a depth of 10.43m the maximum saturation of 77% was reached. The majority of the stations show an increase in saturation with depth until a depth of around 9-11m, where it then begins to decrease. The only stations that do not support this trend are stations 44 and 50. Station 44, shows an almost linear decrease in saturation with depth; similarly, station 50 shows an almost linear increase in saturation with depth, where it reaches the highest saturation recorded at any station with a value of 119%.

Oxygen Saturation

Figure 3.8. Depth profile of Oxygen Saturation at five time points.