Greetings from Pelagia!

by Clare Johnson

As the scientists from RRS Discovery are enjoying being back on land, we are eight days into our scientific cruise on board a Dutch research vessel, RV Pelagia, named after a type of colourful jellyfish. We are a mixed bunch: scientists from the UK, China and US who are all interested in the circulation of the subpolar North Atlantic. Although we’re in nearly exactly the same bit of ocean that Discovery was in less than two weeks ago, the approach of this trip is different. Penny and the team on Discovery made measurements of temperature and salinity at a single point in time at many different locations between Scotland and Iceland. The aim of this trip is to supplement this brilliant dataset with a series of measurements every 30 minutes for at least three years across the entire width of the Atlantic! This should allow us to see how variable important currents are, whether they are weaker or stronger at different times of the year and for us to calculate how much heat and salt is entering the Nordic Seas and Arctic Ocean to the north.

So how do we do this? Well, we don’t expect scientists to be out making measurements continuously for the next 5 years – there would be a mutiny especially as the North Atlantic is not somewhere you want to be in winter! Instead instruments are attached to a wire that is tethered to the seabed using a heavy weight such as several old railway wheels. Last summer we deployed these ‘moorings’ at around 50 locations between Scotland and Canada. Since then they have (hopefully!) stayed where we deployed them, not been damaged by trawlers and dutifully made measurements of current speed and direction as well as water temperature and salinity every 30 minutes. This trips main aim is to (hopefully!) recover the first 13 of these moorings (and the associated valuable yearlong datasets), and re-deploy new instruments to continue the measurements for the next 12 months. Then next summer we’ll be back to (hopefully!) pick these instruments up, get the data off them and put the next lot of instruments in and so on until 2017. I say ‘hopefully’ a lot because although we try and minimise the risk of instruments and moorings failing there is a lot that can go wrong with things that are in the ocean for a year… We have recovered and replaced four moorings in the past week so so-far it’s going pretty well. Fingers crossed it continues to do so!

Photos by Clare Johnson and Loïc Houpert

150625 pelagia at NOC

RV Pelagia docked at the National Oceanography Centre in Southampton

150625 John squeezing the kit into the van

John squeezing the SAMS kit into a small van

150625 mooring kit on NOC quayside

Mooring kit on the NOC quayside before loading onto Pelagia

150625 deploying a mooring west of Scotland

Deployment of a mooring west of Scotland. The rusty chain tethers the instruments to the seabed whilst the orange floats keep the wire and instruments vertical in the water.

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