|Locations of RAPID moorings and where biogeochemical observations will be made.|
The mechanism by which this happens is quite ingenious. Empty plastic bags (that are slightly more bespoke than a humble 5p carrier) are enclosed within sealed acrylic cylinders filled with water. Over the next 15 months or so, every 11 days an external valve will turn to select a new, unfilled bag port, and start to pump the water out of the bottom of the acrylic cylinder. This will create a pressure gradient within the cylinder that will lead to local seawater being drawn through the sample inlet, through a separate part of the multi-position valve and into the bag. A sample preservative placed in the tubing between the bag and the sample inlet will ensure that the chemistry of the water collected will not change between the time it is sampled and the time at which it is retrieved and analysed. When full, the valve turns back to its home position, and the bag and the water sample it contains become, like a desert island, isolated.
|RAS and sensors being deployed at mooring EB1|
|Flower Power: birds-eye view of the multiple tubes leading from the central multi-position valve to individual sample bags / cylinders on the RAS|
|Hillbilly Sprinter: banjo bolt water inlet|
|Part of the ABC sensor suite: pH sensor (black cylinder, foreground), temperature, salinity, pressure and oxygen sensor (silver cylinder with circular-holed guard, centre-ground), temperature/salinity/pressure sensor (below).|
|Other part of the ABC sensor suite: Baby Bear (pump), Mummy Bear (pCO2 sensor), Daddy Bear (battery pack)|
Together, the autonomous samplers and biogeochemical sensors provide a substantial chemical upgrade to the successful RAPID mooring array. In 15-18 months time, the data collected should hopefully shed new light on the drivers and processes controlling short and longer-term variability in chemical fluxes, both within the ocean and at the upper-ocean lower-atmosphere interface. But that’s for the future. As yet only two RAS/pH/pCO2/oxygen sensor sets are in the water at EB1 and MAR1, with more still to come at WB4, WBH2 and WB1. Better get to checking some fittings.
|Splash: RAS and sensors deployment at EB1|
Written by Pete.