Friday, July 1, 2011

Just below the surface

- Graig Sutherland [NUI Galway]

By now you, our faithful blog readers, have been introduced to marine aerosols, eddy correlation fluxes, and gas transfer rates and now I’m going to tell you a little bit about why I’m here. My name is Graig Sutherland and I’m a PhD candidate from the National University of Ireland, Galway (NUIG) studying the physical oceanography in the upper ocean. Surprisingly the upper ocean, even though it’s the most accessible part of the ocean, is one of the most under-sampled regions in physical oceanography. I’m interested in the physics of the upper ocean and how this interacts with the atmosphere. To measure this we use an autonomous vertical profiler ASIP (Air-Sea Interaction Profiler), which was developed by my supervisor Dr. Brian Ward (now at NUIG). ASIP is an ideal instrument for upper ocean physics in that it profiles upwards, making measurements at sub centimetre scales, through the water column to the water surface. ASIP measures temperature, salinity (inferred from the conductivity of seawater), the dissipation due to turbulence (inferred from the small-scale shear), water velocity, ambient sound, and solar radiation coming through the water surface. These measurements can be related to effects from the atmosphere (such as wind, gas transfer, etc.) and vice versa (i.e. effects from the atmosphere can be related to physical aspects of the upper ocean).
The high precision sensors fitted on ASIP are extremely fragile and offer some challenges in how we get ASIP into the water without breaking everything. This is no small feat as ASIP is 2.5 metres long and weighs in at 100 kilograms (that’s 8 feet 4 inches and 220 lbs respectively). To achieve this we need to go out in a small boat and gently place ASIP into the water. The first photo (courtesy of Phil Bresnahan) shows ASIP (with the yellow top) getting ready to go to sea. This is usually a good time (as long as nothing breaks!) and there is never a shortage of volunteers to go out for a little scientific expedition on a small boat. Once in the water ASIP is all on it’s own to make measurements. It descends through the water with the work of three thrusters which pull it down to a pre-programmed depth at which point it freely rises to the surface. Once ASIP reaches the surface it tells us it’s location via iridium satellite so we can track it until it’s time to go out and recover it.
With just over two weeks to go there is ample opportunity to investigate air-sea interactions and to keep looking at what is going on just beneath the surface.

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