FALMOUTH FIELDCOURSE
Group 5
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Offshore boat methodology
The offshore session used both the R.V. Callista and the Terramare to assess whether stratification in the water column varies temporally, spatially or both.
The R.V. Callista was used to measure spatial variability. Five stations were measured in total. The initial ‘shakedown’ station was used to practice the methods being used at further stations. The second site was a repeat station, where the Terramare remained to measure temporal change. The final three stations were spread evenly apart, the final station being the E1 monitoring buoy.
A CTD rosette was used on R.V. Callista to take direct water column measurements. The temperature, salinity and chlorophyll concentration were used to determine where niskin bottles should be fired. Nitrate, phosphate, silicate and oxygen concentration were calculated using seawater samples. The phytoplankton cell count was also recorded. Zooplankton were sampled using a closing plankton net, turbidity and chlorophyll concentration was used to determine the depths of sampling.
The minibat was deployed after the final station (C8) had been sampled, on the return to Falmouth and was towed on 100m of cable. It dived and rose in the water column between set limits whilst recording salinity, temperature, density, turbidity and fluorescence of the water column for 5.5 nautical miles.
The Terramare measured temporal variability, at the repeat station, measurements were taken hourly. Niskin bottles were deployed using a line and messenger and zooplankton were measured using towed plankton nets.
Above: R.V. Callista (Photo credit -
Click below to see a breakdown of our Offshore data
Site Reasoning
Two sites (C4 and C5) were predetermined as both these sites were also being surveyed by Terramare and needed to be sampled by both vessels. After these sites were surveyed, three others were chosen based on numerous factors. One of the factors was the optimum weather conditions on that day (4th July). There was low wind meaning it was very calm, making the sea state ideal for travelling a great distance off shore. This allowed Callista to reach a fixed buoy (E1) run by Plymouth Marine Lab. As there were 18 miles between C5 and E1 it was decided that two additional sites would be surveyed with 6 miles between each site. The equal distance was chosen as Callista was observing how distance affected the biology, chemistry and physics of the water. There was, however, a time constraint meaning samples could not be collected at all sites, but a CTD and ADCP profile was taken at all 5 locations.
Above: MTS Terramare (Credit -