Friday, 21 August 2009

Day 6 – 12th August

Similar to yesterday the focus of the day was on recovering as many of the remaining moorings as possible. We have so far had a 100% retrieval success rate which is usually unheard of. During the last cruise, the success rate was particularly low, so everyone is pretty pleased. I ended up having a pretty relaxed day as I am not that involved with the recovery and data download. During the morning we did complete one further CTD profile that was under the cover of ice last night, but other than that I was mainly processing the CTD data and loading it up into a program called Ocean Data View. This basically allows us to easily compare the data from each cast and allow us to see the variations in the water column resulting from the different currents and water masses within the Nares Strait. For example, the profiles near Ellesmere Island show a much colder and fresher surface water compared to those near Greenland as the main Arctic outflow runs along Ellesmere Island.

There was a bit of drama over lunch when of the moorings decided to pop up under an ice floe. The boats RIB went out to collect it (each mooring has an avalanche transmitter attached so its position can be pinpointed under the ice) but ended up getting the mooring line wrapped around its prop. Eventually the boats second, smaller RIB was launched and it was able to recover both the boat and the mooring.

Although there was no CTD section this evening (first night off on the entire cruise!) we did one test cast with the water sampling rosette system. This contains a second CTD and a rosette of 11 water sampling bottles. An auto fire mechanism is used to fire the bottles are pre-defined depths/pressures. The water bottles are then used to fill a variety of smaller bottles so parameters including oxygen, barium, nutrients, salinity, alkalinity and oxygen 18 can be measured. Sampling water that is usually below zero is pretty tough on the hands!!

I think I forgot to mention what a CTD and ADCP are before so some of the non oceanographers may be somewhat confused! Basically CTD stands for conductivity (essentially salinity although not quite), temperature, depth and is simply used to measure these parameters and more depending on what other instruments you strap to it. They are the bread and butter tool for oceanography as from these simple measurements many more complicated and essential parameters can be derived such as density.
An ADCP is an Acoustic Doppler Current Meter which as the name suggests uses sound to measure ocean currents. It utilises the Doppler effect (the effect that causes the distinctive change in the sound of a train/siren coming towards and then away from you) to determine how fast ‘parcels’ of water are moving and in what direction. They can also detect the backscatter or echo off particles in the water the therefore can be used to indicate the location and density of plankton blooms.
I hope these make sense and sorry for the confusion!!

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