Basics of oceanic internal waves
Baroclinic gravity waves are akin to surface waves we see from a boat, only they are inside the ocean interior. They are undulations of the stratified density surfaces, and they oscillate due to gravitational forces acting on different layers of seawater buoyancy. Imagine oil on top of water, and gently shake the container. You have just created internal gravity waves in the kitchen! For this reason, some like to call these waves "internal gravity" waves, which sounds a bit less sophisticated than the rather technical term ``baroclinic''. But they are really the same thing, just different names.
|Kurt Polzin on the back deck watching the deployment of his mooring. Note the yellow plastic balls near his feet, which are floats to be strung near the top of the mooring.|
What is a mooring?
We reached the mooring deployment site on Tuesday, 21 March near the South Orkney Islands. The mooring will stay in the ocean for about 40 days, after which time we will recover it on the way north near the end of the cruise. One of the uncertainties in this science is whether all of the measurement devices will stay in working order throughout the deployment, and how readily we can recover the information saved when sitting on the ocean bottom.
Deploying Kurt's mooring
|Back deck with the mooring floats (yellow balls) and the crew getting things organized. Kurt is on the right (yellow jacket) and Andy is near the centre with the red jacket. They sky was clear but the winds were blowing and the air near freezing.|
The overall aim is to have instruments placed at selected positions on a cable that is about 4000-5000m long. That is 4-5km!! It is a very long cable, taking many hours of careful winch operation, instrument placement, float placement, etc., all while standing on the back of a ship exposed to the rolling sea. We had plenty of waves on the ocean surface during deployment due to a strong wind (a rather normal occurrence for this part of the world). At least the sky reasonably clear.
Those near to the back deck doing the bulk of the mooring work wear safety cables in case they are swept into the ocean. At our location, the sea surface temperature is very close to freezing. Unprotected, a person will live no longer than a 3-5 minutes in that water. So it is simply NOT an option to fall overboard. Hence, there are heaps of safety precautions, including the cables attached to the work clothes. I took GoPro time lapse of some portions of the mooring deployment, at least for as long as I could withstand the winds and cold standing outside the UIC lab.