Saturday, 5 July 2008

...bumpy seas...

Hello from the bumpy seas! Friday was a very bumpy voyage from Weymouth where we did the calibration to Jones Bank (see the map on left for our route – in black). So there were a lot of green faces (including me & I don’t usually get seasick!). However, there was still a hive of activity getting the moorings ready to deploy. The moorings sit on the seabed with instruments also spread through the water column, and then a big buoy at the surface. The moorings are placed along the edge of the Jones Bank (see map)… this is an area which is a fisherman’s hotspot – so there are lots of fish here, and it’s interesting to the oceanographers because of interesting tidal features which I’ll try and explain later in the cruise (in simple speak because I’m not an oceanographer!).
The moorings will be monitoring over the whole 3 weeks of the cruise lots of interesting things (well we think they’re interesting – that’s why we’re here!):

* ADCP = Acoustic Doppler Current Profiler (see picture on right)
A what? Well this sits on the sea bed and points towards the surface, transmitting a very high frequency sound pulse through the water which bounces off small particles in the water column (like zooplankton – your microscopic animals of the sea), and the reflection is picked up again by the ADCP. This allows the clever oceanographers here to work out how fast the currents are moving & in what direction throughout the water column. So it should show ebb and flood of the tides, as well as currents caused by the layering of the water column (where warmer water sits on top of cold water: the depth at which this occurs is called the ‘thermocline’)… and interestingly the currents travel in opposite directions on either side of the thermocline. This is great because it creates turbulence & mixing between the nice nutrient rich cold water, and the nice warm & sunny (????!!!) top layer – this means it’s good for phytoplankton – the little microscopic plants that allow our seas to be so full of life. Phytoplankton need both light & nutrients, so the thermocline is a good place for them in tidal places like here around the UK.

* Temperature loggers – these are placed at 5 or 10m intervals from the surface all the way to the bottom, and allow us to see where the thermocline is (where warm water changes to colder bottom water), and how it varies over the tidal cycle – both between the high and low tides, and between spring and neap tides.

* CPOD – a porpoise & dolphin click detector (Chelonia Ltd) is attached to each mooring (it’s the creamy tubular device attached to the moorings with lots of cable ties, jubilee clips and lots of gaffer tape curtesy of Em in the picture). These will detect any dolphin or porpoises within 1km of the mooring if they are producing echolocation clicks. Both dolphins and porpoises produce ‘echolocation’ high frequency clicks (higher frequency than we’re able to hear), which are believed to be used for locating prey & probably for navigation. A bit like the ADCP and the echosounder I’ve described: the porpoise/dolphin sends out click sound pulses into the water, and can acoustically ‘see’ fish, the bottom or even our ship from the echoes it hears. The CPOD will listen for & record these clicks so that we can see if there are any porpoises or dolphins around our moorings, and hopefully relate their presence to the oceanography we’re collecting at the same time… i.e. how does porpoise & dolphin presence change with the tidal cycle?

Gosh what a spiel! You can tell I have time on my hands! Well, two of the moorings went in last night before we were beset with 40 mph winds and an even bumpier sea… so that’s why I have time on my hands… we can’t do anything while the seas so rough! So now it’s a waiting game… waiting for the ‘unseasonal July weather’ to pass…

2 comments:

Dr Dolphin said...

I don't envy you bouncing around out there! Keep up the good work and stay safe x

Boulmer Birder said...

A good sensible blog there , I like it. I'll keep an eye on it. I don't envy you stuck out there in the low pressure pattern we have at the minute....Good Luck.