Falmouth Group 8

DISCLAIMER! This website does not necessarily reflect the views expressed by the National Oceanography Centre or any of its staff.

Nitrate decreases sharply from 3.2 μmol/L to 1.55 μmol/L in the surface waters between 1.3m and 22.4m, then it increases to 50.07 μmol/L at the bottom of the profile at 40.5m. Silicon and phosphate show similar profiles in the water column, both increasing at a relatively constant rate throughout. Silicon increases from 1.13 to 2.52 μmol/L.

Nitrate decreases in surface waters due to the biological uptake by organisms. Nitrate is used by organism to make nitrogenous bases used in the backbone of DNA. It then increases again in deeper water found below the 1% light depth due to the breakdown of aggregates falling from surface waters. Silicon and phosphate are both increasing constantly even though they are assimilated by organisms; this is because nitrogen in the surface waters is a limiting factor for growth.

Time: 10:08 (UTC)

Lat: 50 07.406 N

Long: 004 51.150 W

Wind: 340° 10.8 knots

Cloud: 8/8

Nutrients - Figure 5

The graph shows the chlorophyll minimum of 1.64 µg/L is at 1.3m, this increases linearly to the maximum concentration of 2.86 µg/L at 22.4m. The chlorophyll concentration then decreases to 2.25 µg/L at 40.5m. The fluorometry profile agrees with this. The graph shows oxygen rich waters (104.1%) at 1.3m, decreasing to 96.3% at 22.4m and further decreasing to 91.4% at 40.5m.

The secchi depth of 9m suggests a 1% light level at about 27m, this corresponds with the oxygen saturation decrease with depth, and implies that respiration processes dominate.

Chlorophyll and  Dissolved Oxygen - Figure 3

Fluorescence rapidly peaks after 15 m, although the increment is not as large as previously displayed. Values rapidly revert to original surface values as described previously. Temperature begins to decrease from 10 m, although the reduction is not as rapid. Minimal values however still occur just below the fluorescence peak. Salinity only shows a slight increase after 15 m, and irradiance levels still display a similar pattern.

The thermocline is not as distinct here as at the previous station, which may explain why fluorescence values do not increase as much relative to how they did at station 1. A reduced density barrier for nutrients allows phytoplankton to reside nearer to the surface.

CTD  - Figure 4

Backscatter: Backscatter visible as a distinct layer of phytoplankton at  20m, this corresponds to the fluorometer reading and the chlorophyll maximum. On the left half the distinct layer is still visible, but there are small interruptions of low backscatter. An additional second visible layer of high return is seen at 30m, however this doesn’t correspond to any features. This backscatter is an anomaly.

Velocity and direction: The surface to 20m the flow is southwest with speeds of 0.007 m s-1 (the prevailing winds were from the southwest). There is a clear decrease in surface velocity from left to right. There appears to be changes in wind direction, from north-westerly to south-westerly and the current velocity increases. Below 20m the flow is easterly.

ADCP - Figures 1 & 2

Station 2

Click graphs to enlarge