A Niskin bottle was used to collect water samples at 2 depths for each station. All stations were sampled at 2m and at the deep chlorophyll maximum, estimated from the turbidity data from the CTD profile. This was due to technical issues with the fluorometer.

The chemical methods are as used by Johnson & Petty, 1983 for Nitrate, as used by (Parsons et al, 1984) for Silicate and phosphate and as used by (Grasshoff et al. 1999) For dissolved oxygen.

Sample tubes containing the chlorophyll samples taken from.

The nitrate concentration time series shows notable increases and decreases in surface nitrate (0 µmol/l to 0.23 µmol/l then back to 0.06 µmol/l) between 10:00-12:30 UTC and a decrease in deep nitrate concentration (0.13 µmol/l to 0 µmol/l) between 13:45-15:00 UTC. Some data points appear to be at 0 µmol/l, however this may be due to them being below the detectable range of the equipment used (flow through spectrometer).

Figure 5. Nitrate concentration time series taken from MTS Terramare between 09:58-14:45 UTC on 06.07.2017 at 50° 05.420’ N 004° 52.379' W. Samples were collected via a Niskin bottle from 2 different depths, a sample from the surface (2m) and a sample from the predicted thermocline (20-28m).

The silicate concentration time series shows a difference in the concentrations between surface and deep, with deep levels being higher than the surface. Notable increase in deep silicate concentrations (0.25 µmol/l to 0.90 µmol/l) was seen between 12:00-14:00 UTC and decrease (0.90 µmol/l to 0.25 µmol/l) between 14:00-15:00 UTC. There were minimal changes to the surface concentrations

Figure 6. Silicate concentration time series taken from MTS Terramare between 09:58-14:45 UTC on 06.07.2017 at 50° 05.420’ N 004° 52.379' W. Samples were collected via a Niskin bottle from 2 different depths, a sample from the surface (2m) and a sample from the predicted thermocline (20-28m).

Figure 7. Phosphate mixing diagram. Samples collected on boat Bill Conway and Winnie the Pooh the 8th July 2017 from 8:00 UTC to 14:00 UTC. The samples were collected via Niskin bottles attached to a rosette on Bill Conway, and a horizontal Niskin bottle on Winnie the Pooh, from the river Allen to Black Rock.

The phosphate concentration time series shows a difference in the concentrations between surface and deep, with deep levels being higher than the surface. No notable increases/decreases are seen, with minimal changes seen to both surface and deep phosphate. There is a decrease in deep phosphate concentration (0.20 µmol/l to 0.08 µmol/l) between 14:00-15:00 UTC

Disclaimer: The views and opinions expressed are those of the contributors and do not reflect the views and opinions of the University of Southampton

Arrigo, K. (2005). Marine microorganisms and global nutrient cycles. Nature, 437(7057), pp.349-355.

Grasshoff, K., Kremling, K & Ehrhardt. M., 1999. Methods of seawater analysis. 3rd ed. Wiley-VCH, Chichester.

Johnson K. and Petty R.L., 1983.  “Determination of nitrate and nitrite in seawater by flow injection analysis”.  Limnology and Oceanography vol 28, pp1260-1266.

Parsons, T. R., Maita Y. & Lalli C., 1984. A manual of chemical and biological methods for seawater analysis. pp 173 . Pergamon.

The nutrient concentrations appear to correlate with the phytoplankton cell counts (refer to biology section). As deep phytoplankton levels increase, both silicate and phosphate concentrations decrease and increase again after phytoplankton levels fall. This makes sense as phytoplankton use nutrients such as these for growth and thus influence their concentrations (Arrigo, 2005). Nitrate does not seem to follow this pattern however. This could be due to water movement, as over an hourly time scale, advective material is being measured and will be effected by water movement. The data collected here has limited potential for analysis, and is better analysed with complimentary data, such as data the other groups have collected at Falmouth.

The graph shows how Dissolved Oxygen collected from the CTD gives a higher saturation percentage to those collected using the titration method on water collected from the Niskin Bottle. Although there is lower dissolved oxygen within the Niskin Bottle sample there is a correlation between the two plots as it shows decreasing oxygen trend below the deep chlorophyll maximum.

Figure 8. Shows percentage Dissolved Oxygen saturation collected from CTD compared with Niskin bottle water samples against depth.

Dissolved oxygen shows strong correlation with chlorophyll concentrations at depth. This is due to there being high levels of phytoplankton in the area which produce oxygen. Station 16 was sampled below the deep chlorophyll maximum where a dramatic fall in oxygen can be seen as well as a fall in chlorophyll. Surface oxygen levels are higher than surface chlorophyll concentrations as there are little other nutrient in the surface water which will limit primary productivity. This is because the spring bloom has just taken place using up all available resources.

Figure 9. Shows percentage Dissolved Oxygen saturation collected from CTD compared with Niskin bottle water samples against depth.

Overall, the depth of the deep chlorophyll maximum increases between each station. This is shown by an increasing depth high dissolved oxygen and chlorophyll values. Due to increased solar exposure and intensity allowing more light to propagate through the water column allowing more photosynthesis to occur at a greater depth.