Falmouth Group 8

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Salinity at station 6 stays constant throughout the profile from 5.6m to 30.1m at 35.2. Nitrate decreases in surface waters from 12.97 μmol/L to 0.00 μmol/L it then increases in deeper waters to 26.31 μmol/L. Silicon and phosphate both follow the same constant trend, phosphate increasing from 0.036 μmol/L in the shallow waters to 0.231 μmol/L in the deeper waters. Silicon increases from 0.35 μmol/L to 2.15 μmol/L

Nitrate decreases in surface water due to biological uptake; it is totally stripped in the surface waters and is a limiting factor for growth as silicon and phosphate both increase in surface waters. All nutrients increase in deep waters, this is due to the falling of aggregate material from surface waters.

The graph shows very oxygen rich waters at 5m decreasing linearly to approximately 90.8% at 30.1m. Chlorophyll is greatest at 18.8m with a concentration of 5.14 µg/L, which is the greatest concentration recorded across all stations. The lower chlorophyll values are at 5.6m and 30.1m. When compared with the fluorometry profile data, it appears that 20m was the chlorophyll maxima. As the Secchi depth at this station was 6.5m, this also puts the 1% light level at about 20m. This explains the oxygen saturation depletion at 30m, as it is likely below the compensation depth and respiration processes dominate.  

Chlorophyll and  Dissolved Oxygen -   Figure 4

Although not as stable of a profile as the previous station, there is only a fairly gentle linear reduction in temperature after approximately 20 m. Fluorescence values display a gentle linear increase up to 20 m and from then on it decreases at a more rapid linear rate. Once again it remains at its surface value afterwards, though interestingly the reduction is relatively greater than the temperature reduction.

The waters here show some signs of being more stratified than the previous station, although the temperature differences are not quite sufficient to state the presence of a thermocline.  The differences however are sufficient to cause a peak in phytoplankton levels at depth.

Backscatter: A clear layer of high return at 20m corresponds to the fluorometer maximum from the CTD profile. Between the ensemble numbers 230780-231106 the layer splits into 2 layers of high return at 15m and at 25m.

Velocity and direction: There is little variation in the velocity throughout, the direction is east to southeast with a north to northeast band at 10-20m fading out along the transect.

Click graphs to enlarge

Nutrients - Figure 5

CTD - Figure 3

ADCP - Figure 1 & 2

Station 6

Time: 14:00 (UTC)

Lat: 50 10.463 N

Long: 004 53.462 W

Wind: 247° 13.3 knots

Cloud: 5/8