|
|
|
|
|
|
The morning was spent scouring the station for a zinc anode. After recovering the timelapse camera yesterday, we saw that in only 3 days of immersion in the ocean the aluminum plate that is used as a heat sink for the voltage regulators for the strobes was badly corroded. Metal corrosion in seawater is common, especially when there is a small electrical charge, as there is in our camera that is powered from batteries on the surface. To prevent the plate from corroding through and flooding our camera system with all its sensitive electronic parts (see Craig's lament of 11 November), we needed to attach a non-necessary piece of metal that has "looser" electrons than the aluminum. This other metal piece will then corrode, protecting the important aluminum plate. Zinc and magnesium are two such metals. Magnesium has the unfortunate (but rather cool) property of being capable of burning even when immersed in water. On boat engines, zinc anodes are standard items. But with no boats here, they were a tough thing to find. With perseverance, many phone calls, and much racking of several brains, we finally were saved by, of all things, the plumbing department, who removed a zinc rod from a water heater (where they prevent corrosion of the water pipes) and wired it up so we could attach it to our system. This little side escapade took all morning, throwing our carefully crafted dive plan into shambles.
 |
| Our timelapse camera system on the seafloor. The main camera is in the middle housing, with a strobe to provide light out on the arms to each side. |
In the afternoon Craig and I went in at the Outfall South A site, to set up an experiment that will be monitored by the timelapse camera. This system automatically takes a picture every 10 minutes, and allows us to watch the movement patters of seastars, sea urchins, and nemertean worms. I want to know why organics at the outfall are not eaten by seastars, though stars rapidly consume every other organic source available. My hypothesis is that is the bacterial mat that covers the outfall organics that repels seastars. So we placed on the seafloor a tempting smorgasbord, using the organic concoction that Dan carefully mixes in the lab blender, some of it inoculated with bacteria, and some of it not. We have already done this experiment once, at Cinder Cones, with stunning results. Within one hour, stars had completely covered the unprotected organic material, but at the end of three days they still would not touch the bacteria-innoculated organics. This is an interesting example of competition across a wide size- range of scavengers - usually we think of ecological competition as being between two species of relatively equivalent size, but here the microscopic bacteria are beating out the much larger seastars!
 |
| The end of the outfall pipe, with the thick mat of white Beggiatoa bacteria covering all the organics. |
There was an amusing fiasco on our return to the surface. Craig and I had forgotten that the white 5 gallon buckets that we use to carry large items to the seafloor get quite buoyant when they turn upside down and fill with our exhausted air. On returning to the hole at the end of the dive, we saw that the buckets had floated to the surface.or so we thought. Because the holes are continually freezing, despite our valiant daily efforts with chipper bars, eventually the holes become too small to fit a diver through and have to be redrilled. When this one was redrilled, the old hole and the new hole overlapped, creating a perfect edge for a bucket full of air. As Craig ascended, removing his tank, he discovered that one of the buckets had gotten lodged on the lip between the two holes. He made this discovery by getting his tank stuck in the bucket. This reprise of the white bucket drill from Happy Campers School ended with me freeing the bucket and sending it rocketing upward into Craig's chin.
A bit later in the afternoon, Jennifer and Dan dove at Dayton's Wall, and found yet more evidence of the prolific nature of research in that historic era. Having videoed and photoed the rediscovered experiments, they had a much smoother ending to Dan's last dive in the Antarctic for the season. Dan flies home on Friday, and to be safe, we allow 24 hours for the nitrogen bubbles to clear from his blood before he ascends to altitude.
 |
| Jennifer demonstrates proper underwater buddy signaling technique. I leave to your imagination the signal for "incoming white bucket." |
Meanwhile, Craig and Jonna had headed out to the current meter site, and found that the helpful seal who has been assisting in keeping the hole unfrozen has found better hunting (and breathing) grounds. They had some chipping to do in addition to dipping to do a CTD cast and reset the current meter.
 |
| The seal that has been helping with our current meter hole. Notice his small stash of fish (kind of like the little stashes of chocolate in all our our pockets) on the right side of the hole. |
Our evening ended with a science lecture on volcanism on nearby Mt.Erebus. The weather forecast for tomorrow is for 40 kt winds, and the temperature has dropped substantially, but we are hoping that we will be able to make up at least one of the two dives we did not accomplish today, and stay on our tight schedule as we count down our final week.
 |
| Mt. Erebus, the volcano towering behind McMurdo Station. |