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So the way that you read this plot which is from the current meter is like you are looking at a compass. So each of the lines represents one reading of the current meter and the length of the line represents the current velocity and the direction of the line is the direction of the current (up being north, right being east, etc.) This graph just says that the current was northerly through out the time we were testing the meter at the jetty hut. Cool Toy Huh? |
After running up and retrieving the numbers from the current meters, I reset it and loaded it on the piston bully for further deployment. Few current measurements have been taken on the currents too far north of McMurdo and this is relatively easy information to gather assuming you are already down here. Ideally this would be done with a slew of ADCP's but the lab doesn't supply this so we will have to settle for one current meter in one location.
From there we went diving at turtle rock. The first round of divers (Kathy, Aaron, Dan) picked up our newly shorted out time lapse camera (the darn thing overheated (in Antarctica!)) Our resident electronic fix it person (Huck) was then faced with fixing this overly expensive piece of equipment. Then Stacy and I dove on one of the locations that Paul Dayton had set out settling plates twenty five years ago. This was quite exciting although I started out the dive with a cold weather regulator problem. Upon jumping into the water my regulator started free flowing. In the regulator world this a fairly common occurrence. The regulator creates a vacuum opening the valve and starts letting air out and there is no pressure to close the valve again. This really is no problem when in a more temperate environment, one just puts their finger over the mouthpiece creates a little bit of pressure and it seals right up. In the frozen south, it freezes and empties your tank. This happens right at the beginning of the dive so there is no danger involved but it means that you need to get out of the water, switch gear, and then commence diving. Not a big deal except it caused a ten minute lag in the beginning of the dive which Stacy was already waiting for me right under the ice. She kept wondering "I could see his feet where did they go?" Upon my re-entrance to the water we had a lovely dive taking pictures of the plates and looking at the incredible ice structures that formed beneath the ice. It is always amazing to look into a pile of ice and see that a fish (Pagothenia borchgrevinki (or borks for short)) is living in an ice hole. The site was spectacular and hopefully the pictures will turn out.
The day ended with helo flight preparations (i.e. packing) and a supposed early night. Instead we found ourselves enjoying the company from the newly arrived divers from new harbor. We swapped information about our best dives and spots for their stories and info about where to dive in New Harbor, our destination the next day. We fall off to sleep gracious that we don't have to make any more mid night runs to refuel the generator. We get to sleep in tomorrow and that is a welcome break.
Aloha,
andrew
My next step after the staggering into the lab was to run down and pick up a S4 current meter that we threw in the water to see if the settings worked. There are many styles of current meters out there. The most easily to conceive is the water weather vane (but no doubt has a fancy name an associate acronym neither of which I know.) It looks like an arrow with a propeller so you can tell how fast the water is going and the direction. Now, the S4 is very different. It is a sphere which creates a magnetic field around it and by the flow of a conductive liquid (i.e. sea water) it can tell the magnitude and direction of flow. This reduces all sorts of error that is associated with the propeller kind such as not really changing the flow of water at all. Along with this we have a few instruments plugged into it so it will measure the temperature of the water (which all the divers just categorize as cold (it's under the ice)), and then the salinity and depth. The newest fangled thing for the measurement of current is an ADCP (acoustic Doppler current profiler). By turning this device on the surface it will tell you the current speed all the way to the bottom. It works by sending a sound signal through the water column and listening to the change in pitch of the sound as it ricochets off of particles at each depth. Since you can hear the pitch change and you know the speed of sound through the water and the time since you sent the pulse you then can figure out the current speed at each depth. We have an S4 which is still very fancy (and expensive (Thank you NSF!.))