Falmouth Group 13 - 2017

Pontoon - Results

Temperature


The figure shows the temperature profile against time, which shows that the surface layers of water are about 1-2oC warmer than the lower layers. This could be due to warmer fluvial flow overlying colder saline water, or could also be due to solar energy warming up the top layers of the water column. The halocline previously noted could have isolated the surface layers of water, hence making it easier for them to be warmed up by the sun. The temperature profile shows a similar trend to the salinity profile, with temperatures decreasing after the tide turns.


Salinity


The temperature and salinity profiles show two distinct water bodies, with more saline cold water at depth and less saline warm water at the surface. Both of these water bodies were affected by the changing tidal conditions over the time period sampled. Figure 2 shows that there is a halocline of approximately 2 during flood tide, which would lead significant to density stratification between the fresher surface layers, and the more saline lower layers. As the tide begins to turn, the surface waters become more saline & the halocline reduces to about 1.


Oxygen

This figure shows a dissolved oxygen time series with depth and indicates that the entire water column is supersaturated with oxygen. The most likely reason for this supersaturation is primary production, and this is supported by the high levels of chlorophyll that are seen. The surface layer has high levels of oxygen while deeper waters are less saturated. The gradient of high saturation in surface waters and reduced saturation at depth might be due to the respiration depleting oxygen saturation.


Irradiance

This figure shows a depth profile of irradiance in the water column taken every hour. With depth irradiance is expected to decreases exponentially due to the attenuation of short wave radiation both by the water itself and particles suspended in the column. The trends shown are approximately as would be expected, apart from an increase irradiance that is seen at three metres in profiles 2 and 4. This might be due to the pontoon or algae growing on the side of the pontoon shading the top portion of the water column, but irradiance from a different angle being able to reach the water below this depth.


Flow velocity

The figure shows flow velocity depth profiles at each hourly interval. Positive values on the graph represent upstream velocity while negative values show downstream velocity. A change in flow direction can be seen between 13:30 UTC and 14:38 UTC suggesting that the tide turned at some point between these 2 intervals. A difference of up to an hour may be expected between high tide at Falmouth (14:51 UTC) and high tide further up the estuary towards Truro which can explain the difference in these times. Flow speeds tend to be higher at depth than the surface in upstream values. This could be due to the tidal flow moving at a faster velocity than any fluvial flow.


Disclaimer: The views and opinions expressed in this site are solely those of Group 13 and not necessarily the University of Southampton or the National Oceanography Centre, Southampton.