Falmouth Group 8
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Salinity increases between the surfaces and 23.162m where it stays constant down to the bottom of the profile at 42.8m. Silicon decreases in surface waters from 1.10 μmol/L to 0.69 μmol/L at 23.162m silicon then increases to 2.75 μmol/L at the bottom of the profile at 42.8m. Nitrate increases in the surface waters from 0.82 μmol/L to 1.09 μmol/L. It then increases at a greater rate in deeper waters from 1.09 to 1.73 μmol/L. Phosphate increases slowly from 0.085 t0 0.097 μmol/L in the surface waters it then increases at a greater rate from 0.097 to 0.341 μmol/L.
The decrease in silicon concentration can be explained by the biological removal of silicon by silicious diatoms and flagulates in the surface waters. The increase in dissolved silicon in deeper waters below the 1% light depth is due partly because of the dissolution of the silicious tests moving down the water column. Both nitrate and phosphate are utilised more slowly in surface waters as uptake by biological organisms occurs. Nitrate is used by organisms to make nitrogenous bases used for the backbone of DNA. They then increase in deeper waters due to the breakdown of aggregates falling from the surface waters. The salinity increase in surface waters could be due to tidal flow.
Time: 08:45 (UTC)
Lat: 50 05.711 N
Long: 004 52.140 W
Wind: 135° 14.5 knots
Cloud: 8/8
Nutrients-
The graph shows the chlorophyll maximum of 4.21 µg/L is at 23.2 m, the lower chlorophyll values are at 1.9 m and 42.8 m, with the minimum value at 42.8m being 0.98 µg/L. The fluorometry profile agrees with this observation. Oxygen rich waters (109.5%) are at 1.9m, the oxygen concentration decreases linearly to 99.6% at 23.2m, and decrease further to about 94.4% at 42.8m.
The secchi depth of 11m suggests a 1% light level at about 33m, this corresponds with the oxygen saturation decrease with depth, and implies that respiration processes dominate.
Chlorophyll and Dissolved Oxygen-
The fluorometer reading peaks at over 20 m depth and thereafter it rapidly decreases to its original surface level for the rest of the water column. After 15 m temperature likewise decreased where fluorescence peaked, but remains at this reduced value. The salinity value changes very little, whereas irradiance levels from their maximum value display a steady linear reduction with depth.
It is notable that fluorescence peaks at the point where temperature rapidly decreases. The reduction in temperature could represent a thermocline, and the fluorescence values indicate an increased phytoplankton population here. Phytoplankton were likely found in significant numbers at the thermocline due to the cooler, denser water allowing nutrients to diffuse from the depths. Light levels were still sufficient to allow photosynthesis to take place.
CTD-
Backscatter: Surface backscatter and verticle anomalies visible, most likely source
is CTD deployment and the plankton trawling net. Between ensemble numbers 223330
and 223720 backscatter is visible in the water column most likely from the plankton
trawling net. Between ensemble numbers 22159 and 22549 possible CTD backscatter visible.
Phytoplankton backscatter clearly visible as a continuous layer at depths of 10-
Velocity and direction: The surface water to 20m depth m the flow is south, southwest
at ( 0.2 m s-
ADCP-
Click graphs to enlarge
Station 1