Falmouth Field Course 2017

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Metadata

Date: 11/07/17

Time: 07:05-14:15 UTC

Tide:

- High water: 6:31 and 18:42 UTC

- Low water: 00:41 and 12:55 UTC

- Spring Tide

Environmental conditions:

- Cloud state = 8/8

- Calm sea state (2) with increasing sea state as we moved into open water (5), decreasing again as we moved inshore. Southwest winds in the afternoon

- Light to moderate rain

Equipment Inventory

Introduction

The formation of coastal fronts make the coastal ocean system a highly dynamic and complicated region of oceanography, especially when compared to the relatively more simple open ocean. To see if such a front had formed just offshore of the Fal estuary, a spatial investigation into the biological, physical and chemical properties of the water was carried out on the 11th July 2017 on board the RV Callista. The investigation consisted of taking six depth profiles at separate stations along the coast of Falmouth using the CTD rosette, which was able to measure temperature, salinity, chlorophyll, turbidity and depth, enabling us to analyse the structure of the water column. The rosette also contained six niskin bottles, up to three of which were fired upon recovery of the CTD; this allowed us to choose only areas of interest to sample. In addition to the rosette, an ADCP was used to collect physical data on each station, and a 200um zooplankton sweep net for biological data ie plankton samples. By collecting all this data, the water at each station could be fully surveyed to find out if a regular pycnocline or a coastal front which a chlorophyll maximum was present.

CTD

ADCP

Plankton Trawl (Bongos)

Figure 1. Map of offshore survey area with sites C38-C43

Methodology

During the investigation three pieces of equipment were used to gather data; a CTD Rosette, an ADCP and a 200um plankton net. Metadata was collected at each station before deploying the equipment ie time and location. In order to safely deploy the CTD rosette off the stern of Callista, communication between the computer operators and the members of the team on deck was critical, and so a team member acted as a messenger relay between the two areas. As the CTD was lowered, information was recorded on screen detailing temperature, salinity, chlorophyll, depth and turbidity. From this downward profile it was possible to identify potential zooplankton and water sampling depths. We routinely took surface and bottom water samples at each site as well as taking intermediate water and zooplankton samples in areas of interest eg. the chlorophyll maximum. Our samples were preserved onboard in the wetlab and then processed on land on 12.07.17. The methods for this are as detailed in ‘Lab Protocols’. Additionally we maintained an ongoing adcp time series at each of the 6 stations in order to quantify the current conditions below the vessel.

Table 1. Offshore Site Metadata