Disclaimer: The above statements and views are those expressed by the team members of group 5 and do not reflect those of the University of Southampton or the National Oceanography centre staff or other students

Offshore

During the summer months, stratified water columns occur in offshore waters due to decreased wind, and warming from the sun, creating a thermocline.

Our Aim: for the offshore investigation was to locate the chlorophyll maximum at the tidal mixing front and assess the change in chemical composition of the water column as we moved further from the shore.

We completed our data collection on 23rd June 2015 starting at 08:15. As the weather conditions were optimal, our proposed trajectory of sampling to the suggested station C was adjusted allowing data collection further out to sea  to sample an additional site, station 7. On returning from station 7 to Station 12 a profiling transect was conducted as shown on the map above.

Onboard Callista the CTD was deployed at each station with Niskin bottles attached to the rosette, Sensors that were deployed attached to the CTD included; light sensor fluorometer and a transmissometer recording the chlorophyll maximum and the light attenuation respectively.

With referral to the profiles observed Niskin bottle firing depths were decided. The water collected becomes sealed inside at the desired depth to prevent contamination across layers of the water column. Water from the Niskin bottles were taken into the Callista wet lab, samples were filtered to remove particulate matter and stored for later dry lab analysis for nitrate, phosphate and silicon concentrations. In order to collect phytoplankton, the water samples were placed in bottles with a small amount of iodide to stain the phytoplankton for later microscope identification. Chlorophyll samples were filtered 3 times and the filter paper stored in 100% acetone. Three different depths were sampled at stations 5,6,7 & 12. Stations 8,9,10 and 11 only had samples taken at one depth due to a homogenous water column apart from one enormous chlorophyll peak around 25m. Samples were placed in a fluorometer to determine their fluorescence. The concentration of the chlorophyll was then calculated by:

(volume of acetone/volume of sea water) x fluorimeter reading= chlorophyll /mgL-1

A secchi disk was deployed at each station to measure euphotic zone depth to compare with the transmissometer. A 200nm closing plankton net was also deployed at several stations to sample for zooplankton communities throughout the water column

The ADCP was continuously running between each station and along each transect

Date: 23/06/2015

Time: 07:25-16:12 UTC

Location:

50 07.521N 004 58.683W       

50 05.654N 004 52.305W

Low tide: 03:38, 15.50 UTC

High tide: 09:20, 21:35 UTC

Wind: 2 knots- 8.2 knots

Cloud cover: 1/8th- 7/8th

Vessel: R.V Callista

Map of the offshore waters of Falmouth with group 5 sample sites labelled. Red sites were sample stations whilst yellow sites occurred along the transect. Click to view station location from another angle.

Ash, Fia and Charlie retrieving the CTD on board Callista.

Methodology

Site Location

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