Whisky at last …

by Clare Johnson and Karen Wilson (SAMS)

The time had finally come for the SAMS group onboard to deploy our bright pink seaglider named Jura. We could not have asked for better launch conditions, again the North Atlantic has been kind and we have calm seas and sunshine. We really have been spoiled with the weather so far.

At SAMS, we have seven seagliders, each named after a whisky, the national drink of Scotland. Today it’s Jura’s turn to begin her maiden mission – to monitor the upper waters of the eastern Subpolar Gyre – the first glider measurements within the OSNAP programme.

Seagliders are designed to glide downwards, to a maximum of 1000 m, and back to the surface simply by changing their buoyancy and the location of the heavy battery pack within the glider. As no propulsion is required they are very energy efficient, meaning that they can be deployed for several months at a time. Although the gliders are autonomous, gliding their way between pre-determined waypoints, a team of pilots – based at the North Atlantic Glider Base at SAMS – monitors their progress and changes various parameters to ensure optimum performance. [We are both pilots in training!]

As Jura moves down and up through the water column, sensors measure the temperature and saltiness (salinity) of the water and its dissolved oxygen concentration. Each time the glider reaches the surface the data, along with the gliders position, is transmitted to the pilots via satellites giving near real-time information. By calculating the difference between the actual position of the seaglider after a dive, and its presumed position, the integrated currents between the sea surface and 1000 m can also be determined.

A great benefit of seagliders is that they can make many profiles through the upper water column over a number of months for a fraction of the cost of ship-borne measurements. Seagliders can also operate over the Winter months when it is often too rough to safely make measurements using more traditional methods from a ship, not to mention deeply uncomfortable! This removes a bias in data toward the summer months. [As an aside – the largest waves ever recorded (29 m) were in the eastern Subpolar Gyre in February 2000]

It was a great relief to us that our first glider launch went without incident and after slipping the line free we watched as Jura began its first dive for OSNAP.

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