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>Seas: What seas? Calm
>Winds 3 knots
>Temp -1.1 C ; w/ wind chill –1.1 C
>Location: Latitude 65 degrees 14.12’ S; Longitude 66 degrees 57.44 W

Above, A plankton tow on a brilliant day.
Below: An iceberg with character.
Click on each image for larger view.

13 December 2004

You no doubt have noticed that we didn’t move in the last two days – that’s obviously incorrect and I forget to change the data on our position and conditions. It has been another lovely day in Antarctica. The seas are flat, the sun was occasionally visible, its warm (the first day without a "wind chill"), and the work was interesting.

As I mentioned in yesterday’s note, today started with a catastrophe — the net of the Blake Trawl disappeared (no doubt a victim of a hungry rock). Fear not, we had another net, and it was soon deployed. On its maiden trawl, the new net successfully captured two large boulders. In addition to these pieces of granite, which were probably transported and dumped from an iceberg, we collected a wealth of incredible animals. Of greatest interest to our household was yet another species of pterobranch. This species was also brooding embryos within the tubes that house the adults. Each new find brings hours of fun and delight.

We also have been performing an experiment on the effect of the method of plankton collection on the apparent taxonomic distribution and abundance of larvae within the samples. The traditional procedure used to capture plankton is to tow the net of a certain diameter mesh (typically 202 _m) through the water at a speed of 1-3 knots. As invertebrate larvae live in a world without hard surfaces, they normally have very soft bodies (with the notable exception of the arthropods — i.e., crabs). You might think of their bodies as being made of Jell-o, and I think that you might be able to predict what happens to these larval forms when they are collected using a fast traveling net (what would happen to Jell-o if you pushed it against a screen?). It is not a pretty sight, but despite their appearance you can count the number of larvae in the sample. Or can you?

Dr. Balser and I are advocates of a so-called "Drift Tows." As the name implies, the net is deployed and the vessel drifts due to wind and ocean currents at a very slow speed. This is a much gentler means of collecting material, and the larvae arrive in the laboratory in superb condition and can be used immediately for experiments or preservation for morphological examination. So what happens when you compare the number of larvae collected using these two methods? Any time the net is deployed, the towed net will process more water and, hence, the sample should contain more larvae. We have found just the opposite result. Slower, gentler plankton tows collect more larvae. We can explain this paradoxical result through a loss of larval forms in a towed tow because they are physically destroyed while the net is dragged through the water. Yet another reason that you should always evaluate your assumptions when performing any study.

We’re passing through more and more ice as we proceed north. The underside of the ice is green in color. How can this be? We’ll discuss this phenomenon tomorrow.



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