Offshore

Figure 1. Track from RV Callsta’s onboard computer showing sampling stations.

Chemical Findings…

Station C42 was sampled at 8.08m and 24.70m and shows a decrease in temperature 16.7°C to 15.9°C with depth. This station shows a slight increase in salinity with depth, from 35.07 PSU to 35.09 PSU. Nitrite at 8.08m was 0.009umol/L and decreased to 0.007umol/L at 24.7m. Nitrate concentration was 0.668umol/L at 8.08m and rapidly decreased to 0.00umol/L at 24.7m, suggesting it is used up as it travels down the water column. Silicate was 0.038umol/L at 8.08m and it decreased to 0.021umol/L at 24.7m. Phosphate concentration was 0.075umol/L and 0.087umol/L at 24.70m. The oxygen saturation at this station was supersaturated, at 100.5%, and oddly increased to 103% at 24.70m. This shows an addition of oxygen to the water at depth.

 STATION C42

SILICATE

Station C43 shows both a decrease of temperature and salinity with depth, from around 36 PSU and 16.7°C close to the the surface (6.9m), to 35.1 PSU and 16.5°C at the lower depth (19.38m). Nitrate levels at C43 remained the same at 6.9m and 19.38m, where they were both 0umol/L. Nitrite levels slightly increased from 6.9m to 19.38m, from around 0.007 to 0.015umol/L. Phosphate also increases minutely from the shallower to the deeper depths, barely changing from around 0.08umol/L. Silicate increases from 0.13umol/L at 6.9m, to 0.26umol/L. The oxygen saturation % at this station was 95.3% at 6.9m and decreased to at 92.75% at 19.38m down, showing how a removal of oxygen occurred from the surface to the deeper level.

 STATION C43

SILICATE

Station C44 was sampled at depths of 13.06m and 25.24m. Temperature was 16.58°C at 13.06m and decreased to 15.91°C with depth. Salinity at this station increased slightly, from 35.09 to 35.10 PSU at 25.24m. Nitrate increased heavily, from 0umol/L at 13.06m to 0.59umol/L at 25.24m. Nitrite on the other hand remained at 0.01umol/L for both the depths sampled. Silicate also remained the same at both depths; staying at a value of 0.00umol/L. Phosphate increased from 0.6 to 0.8umol/L with depth. Oxygen saturation was 96.5% at 13.06m and increased to 103.2% at 25.24m, which shows an addition of oxygen to the water column between these depths.

STATION C44

SILICATE

Station C45 was sampled at 3 depths: 15.67m, 25.27m and 49.87m. The temperature decreased from the surface down, but the biggest change occurred between the first two depths; 16.68°C at 15.67m to 15.15 degrees at 25.27m to 14.29°C at 49.87m. The salinity at this station increased from the first two depths and then remained the same for the deepest: 35.10 PSU at 15.67m to 35.12 PSU at 25.27m, where it remained for 49.87m. Nitrate was 0.25umol/L at 15.67m and rapidly decreased to 0.00umol/L at 25.27m, suggesting removal from the surface, but then it increased again to 0.08umol/L at 49.87m. Nitrite remained at 0.00umol/L for all three depths. Phosphate increased from 0.05umol/L to 0.07umol/L at 25.24m and finally to 0.95umol/L at 49.97m. Silicate remained at almost 0.00umol/L from the first two depths, but then jumped to 0.29umol/L at the deepest. The oxygen saturation level at 15.67m was relatively high, at 98.4% and then it decreased to 94.5% at 25.37m and decreased even more to 91% at 49.97m, showing a gradual removal of oxygen down the water column.

 STATION C45

SILICATE

At Station C46, only one niskin bottle was fired and so no comparisons could be drawn.

Station C47 was sampled at two depths: 15.27m and 37.3m. The temperature decreased with depth: from 16.83°C to 14.89°C. Salinity also decreased with depth, from 35.12 PSU at 15.27m to 35.11 PSU at 37.3m. Silicate concentration remained at 0.00umol/L, as did the concentration of nitrite in the water. Phosphate increased slightly from the depth 15.27m to 37.3m from 0.05 to 0.07umol/L. Nitrate increased heavily from 0.03umol/L at 15.27m, to 0.525umol/L at 37.3m. The oxygen saturation % at 15.27m was supersaturated, with 104.5% but then it decreased relatively steeply to 98% at 37.3m, showing a rapid utilisation of oxygen between those depths.

 STATIONS C46 AND c47

Figure 5. A plot of temperature and salinity including nutrient and oxygen concentrations plotted against depth for the offshore station C42 from data collected on RV Callista on 10/07/18.

Figure 6. A plot of temperature and salinity including nutrient and oxygen concentrations plotted against depth for the offshore station C43 from data collected on RV Callista on 10/07/18.

Figure 7. A plot of temperature and salinity including nutrient and oxygen concentrations plotted against depth for the offshore station C44 from data collected on RV Callista on 10/07/18.

Figure 8. A plot of temperature and salinity including nutrient and oxygen concentrations plotted against depth for the offshore station C45 from data collected on RV Callista on 10/07/18.

Figure 9. A plot of temperature and salinity including nutrient and oxygen concentrations plotted against depth for the offshore station C47 from data collected on RV Callista on 10/07/18.