[editor’s note, by Jason] Jon Warrenchuk is currently participating in NOAA’s 2004 Gulf of Alaska Seamount Expedition.
August 6, 2004: Last night we launched the CTD. Marine biology is fairly light on acronyms, but this is one we throw around often. “C” stands for conductivity (a measure of salinity), “T” for temperature, and “D” for depth. Perturbations and combinations of those 3 factors (salinity, temperature, and depth) are primarily responsible for patterns of life in the ocean. This particular CTD also measures dissolved oxygen, another important limiting factor for marine life.
The CTD device is tethered to the Atlantis with fiber optic cable, and displays real-time data to the computer lab as it’s lowered to the ocean floor. What’s surprising is that dissolved oxygen decreases significantly after 200 meters depth and the water actually becomes quite “hypoxic” (low in oxygen). But after 1300 meters depth, dissolved oxygen increases. On seamounts that transcend this depth range, zonation of organisms is as evident as it is on a tidal seashore. It’s cold on the bottom too, a consistent 1.6 to 2 degrees Celsius.
The best part about launching the CTD at night is that the boat is stationary and all the deck lights are on. When this happens, you never know what might ascend from the depths. Schooling forage fish, attracted to the lights, flash about in silvery streaks. A squid, about 3 feet long, quietly ascends, hovers, then disappears out of sight. I waited patiently for a salmon or two to make an appearance, but no luck.