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March 29, 2003: Leg 3, Day #19

Carmen Basin

Last night as we moved northward from Farallon Basin, we encountered stiff winds from the northwest. This morning the Galley's white board advertised "bunk  seat belts$5."

While she is usually very stable, the R/V Western Flyer can be pretty lively when she's moved  by strong external forces. The latter were much in evidence this morning and early afternoon. That translates to no ROV diving, so Jeff Drazen began a series of net hauls to keep us working. In the lab, Bill Hamner coaxed some Bathochordaeus, collected yesterday by the blue-water divers, to begin building their filter houses in an aquarium. Later on, Ian Young, the Western Flyer's Captain, and Chief Pilot Buck Reynolds agreed that the winds had dropped sufficiently and that the seas were moderating (scientists always think that, which is why they aren't running the show). We launched ROV Tiburon at about 1600 hours for our first dive into Carmen Basin.

As we descended, we noticed a shallow layer of Bathochordaeus, similar to the one we saw in Farallon Basin just yesterday. But the layer of sinkers we had seen there was not present. Likewise there were cyclosalps present here but in fewer numbers and much more diffusely distributed. (Yesterday, one of our shipmates suggested that if we'd just change their name to psychosalps we could get funding from the National Institute of Mental Health.) Below the salps were some Thalassocalyce ctenophores but also in reduced numbers. Finally, the strong sonic scattering layer we saw in the water column of the Farallon Basin did not appear here.


Why was there such a difference between the layering pattern of animals in this place and the pattern we saw repeatedly just a few kilometers to the south? The depth of the sea floor between the two basins (the sill depth) is about 1,500 meters, far too deep to have an influence on the upper 500 meters where these patterns develop. Was it the wind? Currents? We don't know yet but there is an interesting difference in the shape of the oxygen profile, right at the depth where the contrasting animal distributions occur. It may be that mixing  extends deeper in Carmen Basin, carrying more oxygen with it, and thus increasing the vertical range that these animals can occupy. That doesn't necessarily explain the dearth of sinkers, or why the SSL was so skimpy, but hey, we just got here.

Meanwhile, back in the lab, Brad Seibel was measuring the oxygen carrying capacity of the respiratory pigments of several species. In addition, he is attempting to measure the oxygen consumption rates of Bathochordaeus and Cyclosalpa to help us determine if it really is oxygen levels in the water that shape the vertical distribution of these animals. Often, the answers to these kinds of ecological puzzles are right where you expect them. Sometimes they come out of left field.

As the end of this leg of the expedition draws close, we are scrambling to get as much data as we can generate to finish off our projects. With seven separate projects underway at once, it has been a challenge to keep the data flowing to all. We have made a plan for the final couple of days that will let us continue diving and working right up to the last possible minute. If the weather cooperates, it might just happen... 

Bruce Robison

 

Mar29_00_57_29_04.jpg (52209 bytes)

 

While this looks like an exploded experiment in omelette class, it's a medusa named Phacellophora, found very much deeper today than we have ever seen it before.

Mar29_01_02_01_11.jpg (42199 bytes)

 


Dosidicus
inks ROV Tiburon and stands off the Phacellophora.

Mar29_00_53_48_10.jpg (41668 bytes)


Triphoturus mexicanus, the most abundant midwater fish species in the Gulf. Many of them are oriented like this, either head up or head down as we come upon them during a dive. That's another puzzle because it means they aren't using their ventral photophores for counter-illumination, which is what we were all taught they were for.

 

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