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References:
Sharples, J., Tweddle, F. J., Palmer, M., Green, M., Kim, Y., Hickman, A., Holligan,
P., Moore, M., Rippeth, T., Simpson, J., Krivtsov, V., 2007, ‘Spring-
Paytan, A. and McLaughlin, K. 2009, ‘The Oceanic Phosphorous Cycle’, Chemical Reviews,
107, (2), 563-
Offshore-
Nitrate
Nitrate concentrations increase with time at the surface, however; at the chlorophyll maximum concentrations increased at first but then began to decrease with time. This is due to nitrate being taken up by phytoplankton over the course of the day for their growth. Concentrations of nitrate tend to be higher in surface waters due to there being lots of photosynthesising organisms which use nitrate as an essential nutrient in light and dark reactions.
Nutrients
Silicate
Silicate concentrations are higher at the chlorophyll maximum than at the surface due to there being increased numbers of phytoplankton at this depth. Some species of phytoplankton e.g. diatoms, use silicon to build their tests, which would lead to the increased readings at these depths.
Phosphate
Phosphate concentrations are also higher at the surface than at the chlorophyll maximum. At the chlorophyll maximum, concentrations are low throughout with a slight increase as time increases. Phosphate concentration at depth is the lowest of all the nutrients tested therefore it may be possible that, in this environment, phosphate is one of the most limiting nutrients on growth of phytoplankton. It would be useful to compare the nutrient concentrations shown here to the amount of chlorophyll present in the water column at this time.
Chlorophyll
Chlorophyll data shows two fairly different trends at both 2m and at the DCM. Overall, chlorophyll is greatest at the DCM, but most notable is the peak within the DCM just after 11:00 (UTC), this is likely to represent a brief bloom in phytoplankton numbers. Although concentrations are much lower at 2m, chlorophyll tends to increase steadily throughout the sample period, which could be linked with the incoming tide.
Oxygen
Much like chlorophyll, oxygen displays different trends at the two depths – but they
do not necessarily correlate. As to be expected, oxygen saturation is greatest at
the surface where air-
Conversely, Oxygen saturation at the DCM displays a steady decline throughout the sample period followed by a rapid increase. Predictably, oxygen saturation mirrors chlorophyll at this depth, although there is a lag between minimum oxygen saturation and maximum chlorophyll concentration.
Procedure
A CTD was used to take water samples at the five different stations within the Sampling Site. One sample was taken at the chlorophyll maximum and one at surface for every station, by firing a Niskin bottle.
Lab Analysis
Water samples were then collected into bottles to be analysed in the ashore lab. Samples for phosphate, nitrate and silicate analysis were pipetted into collection bottles through a filter, in order to remove larger molecules. Samples for chlorophyll were pipetted through a filter at 50ml volume and the filter paper was then placed in. Samples for oxygen were placed in glass bottles ensuring no air bubbles were present and then 1ml manganese chloride solution was added, followed by 1ml of alkaline iodide solution to precipitate the oxygen.
The samples were then taken to the in shore lab for further chemical analysis.
Figure 1: Nitrate concentration at 2m and 25m against time [UTC]
Figure 2: Silicate concentration at 2m and 25m against time [UTC]
Figure 3: Phosphate concentration at 2m and 25m against time [UTC]
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Figure 4: Chlorophyll concentration at 2m and 25m against time [UTC]
Figure 5: Oxygen concentration at 2m and 25m against time [UTC]
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