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Aim

To analyse physical, chemical and biological changes over stations offshore of Falmouth.


Objectives

To investigate vertical zooplankton and phytoplankton diversity over different stations offshore. To investigate salinity, temperature, fluorometry and transmission along a vertical profile at each offshore site. To investigate oxygen saturation, chlorophyll, phosphate, silicon and nitrate concentration along a vertical profile at each offshore site. To investigate flow at and between stations offshore.  


Introduction

On the 28th June 2016 we completed an offshore investigation off the Falmouth coast aboard the RV Callista. We headed out to our first station (39) which was the replicate station for all groups. The weather started off dry but conditions offshore deteriorated to being rough and rainy causing us to come off course and came back closer to the shore for the rest of our sample sites. The tide times was low at 4.59 UTC (1.2m), 10.59 UTC (4.4m) and low at 17:27 UTC (1.3m).


Methodology

On arrival at a station we first deployed the CTD rosette to the bottom depth, then looked at the water column for significant changes and choose depths to deploy Niskin bottles. We then brought up the rosette closing up to 4 niskin bottles depending on the  structure of the water column at the site. We then took water samples for oxygen calculation and added Manganous Chloride and Alkaline Iodine to the sample. We also took water samples for nitrate and phosphate which were stored in glass bottles and samples for silicon which we stored in plastic bottles. The chlorophyll was measured by taking 50ml of a sample and passing it through a filter, the filter paper was then stored in acetone. Finally water samples for phytoplankton were taken and stored in bottles. To collect zooplankton samples we used a plankton net (200um) and conducted vertical samples between a range of depths. After being retrieved, the net was washed to get a complete sample and then put into a bottle and formalin was added to kill the organisms. The Minibat was put into the water column on leaving the site and was dragged for the distance until the second site.


Offshore

Time lapse on Callista

callista.mp4

Equipment

Fig. 2 Map of sampling locations offshore on the 28/06/2016

Fig. 1  Summary of factors from sample sites offshore on  28/06/2016

Rosette with CTD, Fluorometer and Transmitometer

Minibat

Plankton net

Rosette

Manufactured by General Oceanic, model 1015. This is a special circular rack which are very durable and incorporated an array of instruments such as Niskin bottles, CTD, etc. It is lowered by the A-frame into the water column at desired depths for sampling as it is fitted with depth sensor.


CTD

Manufactured by Applied Macrosystem Limited (AML), S/N 4183. This instrument carries sensors which are used to determine the conductivity, temperature, and depth (pressure) of the ocean.


Fluorometer

Manufactured by Wetlab, S/N WS38-400P. This instrument measures chlorophyll-a (phytoplankton) in the water column.


Transsiometer

Manufactured by Sea Tech Inc., S/N T1015, Path length 50mm. This instrument projects a laser in-situ, and the scattering of the water column will reduce the voltage detected at the receiver’s end. Hence it shows the presence of mineral fines and turbidity of the site.

MiniBat

It houses the CTD and undulates throughout the water column allowing continuous temperature, salinity, density and flourometry profiles along the transect


Plankton Net

Mesh size 200 micrometer and diameter 52cm. The ultra-fine mesh collects tiny plankton from the water. A wire hoop is attached to a funnel-shaped net and a collecting bottle is placed at the end of net. Net is towed vertically or horizontally and a flowmeter is attached to show the number of rotation and distance covered.