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GEOPHYSICS

TAMAR SAMPLING

OFFSHORE

REFERENCE

PLYMOUTH FIELD COURSE 2019

About the survey

Between the 3rd and 9th July 2019, we carried out a series of surveys at the Tamar Estuary, the off shore L4 station and the breakwater zone of the Plymouth Sound;  to give biological, chemical and physical data to be used to understand the environmental processes and their effect on the fauna and flora of the region. Plymouth Sound and Estruary systems hosts many nationally rare species due to its uncommon environmental set, hence make any scientific data about the region important to develop strategies to recover and protect the habitats. The surveys carried out include: habitat mapping of the Breakwater zone using sidescan sonar and towed video system; water sampling along the Tamar estruary for analysis of salinity, nutrients and chlorophyll; and both depth profiles and sampling for a selection of sites stretching out south from Plymouth breakwater to past Eddystone Rocks.

Geophysics

One of the surveys, undertaken with intent to provide a biological viewpoint of Plymouth sound, was to create a habitat map of an area south of the breakwater. This involved three different techniques which would all be pieced together to create an accurate representation of the chosen site. The first, and most useful, technique was to perform a sidescan sonar survey of multiple parallel tracks covering the area and to piece together these printed traces; then scaling this down onto a track plot. The next technique was a towed-video system that intersected through the sidescan tracks and gave a clear visual representaion of the boundary between different habitats. The final technique was a sediment grab which gave a biological view of the benthic environment.

Tamar Sampling

Another aspect of this study was periodic sampling of the chemical content and plankton abundance along the Tamar estuary, starting at approximately zero salinity and finishing as the salinity reached sea-level. This was performed by two separate groups covering both halves of the estuary, and used various techniques varying from a net trawl to on-board filtration and chemical dilution. These samples and data were then taken to the lab for analysis; with each different sample type undergoing specific treatment for lab analysis.

Offshore

The final section of this investigation focused on offshore data; with both CTD depth profiles and Niskin Bottles being performed at five different sites spaced near-evenly from close to Plymouth Sound (50°18.24’N, 004°08.29’W) and finishing south of Eddystone Rocks at (50°05.95’N,004°14.92’W). At each site, the CTD measured: temperature, salinity, fluorescence, PAR, CDOM, turbidity and beam transmission. Whilst the bottles fired at each site would give data about plankton numbers and oxygen concentrations; after lab analysis and chemical alteration.

TOW FISH

Scanning the Plymouth sea floor .

Tow fish are invaluable in habitat mapping – allowing for quick results that can easily be visualised, with side scan sonar. Aboard the Echo explorer, we explore this effective way of detecting substrate types and topography, also with the use of a video drift and sediment grab.

FLYING PIG AND PORKY PIG

Sampling on RIBS in Tamar Estuary.

The collection and analysis of nutrients, phytoplankton, zooplankton and chlorophyll samples were done on RIBs called Flying Pig and Porky Pig,to determine the extent of mixing that occurs in the Tamar.

ON THE CALLISTA

Offshore data collection on Callista

Using a CTD, data was collected offshore to determine dissolved oxygen content, chlorophyll concentration, Photosynthetically Active Radiation, alongside other parameters. Vertical nets were also used to sample phytoplankton.