May 15–June 3, 2005
Please visit the Ridge 2000 website for additional information.
May 26, 2005
Today's goal was to locate and sample the Mussel Valley vent field first visited in 1989 by French researchers. The name implied we would find heaps of mussels for Cindy's mussel pot work. So much for names; we saw no signs of a vent locality or mussels and worried that the latitude and longitude we used for the dive target were incorrect. Where we landed, we just saw a flat plain covered with copious flocculent sediment that had no earmarks of hydrothermal origin. We wandered about the target for some time and then decided to explore an adjacent mound that was indicated in the bathymetric map we generated the night before. It took over 4 hours to drive the sub to the mound that was only about
3.5 kilometers away! We searched it thoroughly, and again, no signs of recent hydrothermal activity in the area.
But no dive comes up completely empty. We collected a stalked crinoid (image on right), an ancient relative of sea stars. The fossil record is rich with these primitive echinoderms. Thought to be extinct, these living relics were re-discovered in the late 1800's by the Norwegian priest/biologist Mikael Sars. Morphologically defined crinoid species, whose family tree goes back several hundred million years, can still be found. Being able to trace your genealogy back to the Paleozoic is the epitome of biological success. We also collected four different kinds of sponges for Susanne Schmitt, who was very happy with them.
To increase our chances of finding the vent tomorrow, we decided to conduct a CTD survey of the area. The CTD sensor was lowered down twenty-six hundred meters, nearly the bottom. CTD stands for Conductivity, Temperature and Depth. Measuring temperature and depth is obvious, conductivity is a little more esoteric. Seawater is rich in dissolved substances like salts, metals and compounds of an almost infinite variety. These substances influence the way seawater conducts electrical energy. By passing electrons through the water sample, researchers can estimate the salinity. There is also, a transmissivity meter which can detect particulate matter in the water column. Vent water tends to have a lower pH and salt content than the surrounding seawater. The CTD device can detect the elevated temperature of a hydrothermal discharge, thus detecting the presence of vents. The location of the CTD then helps us to target places to dive and look for vents.
The CTD is mounted on a platform, which also contains 24 water-sampling chambers called Niskin
bottles. These bottles can take samples at various depths. The water samples can then be analyzed for suspended material called flocculent or detritus, chlorophyll that signals the presence of algae, and other chemical properties. A computer will open one of the Niskin bottles at prescribed depths, the sample will be taken and the door closed. This preserves the sample's integrity. If samples are taken a various depths, oceanographers can see how temperature, salinity and organic composition vary vertically in a given
area. The CTD sensor detected slightly increased temperatures and suspended materials in the water, which signals the possible presence of our target vent. These means organisms might be collected tomorrow.