This has been an exciting day for many people on the ship as we have been recovery the landers that were deployed last night. During the night the creatures of the abyss have enjoyed the company of three of our landers; ISIT, PAL, and the amphipod trap.
First up was ISIT. The release signal were given at 9am and both acoustic releases fired perfectly, letting go of the ballast and allowing ISIT to rise. About an hour later the floats surfaced and the lander recovered. A shipload of researchers, students and crew were anxious to see what the light sensitive cameras had caught on tape, and after some creative on-the-spot engineering we were able to watch it. In what one would think to be a world of complete darkness, a firework of bioluminescence appeared. The first glimpses of the recordings were spectacular, now it’s up to the researchers to go home and start analyzing them.
Next in line was the amphipod trap. Same recovery procedure was repeated, the trap got on board where we were all waiting for the first actual life forms on this cruise. Unfortunately the trap was empty, the bait untouched. Well, the amphipod trap will get more chances, better luck next time.
What is a CTD?
A CTD test followed. Don’t know what a CTD is? Not to worry, here comes a short explanation. The term CTD is made up of Conductivity, Temperature and Density, which are measurements of important parameters in the sea. However, every time we conduct a CTD test we also take water samples to measure the plant biomass, nutrients and optical properties. This is done to ground truth satellite imagery.
The plant productivity was measured, but in this area it is very low, almost as in a desert. However, in the amphipod trap, lots of gelatinous Salps (little jellyfishes) were found which possibly ate all of the plants.
The CTD mooring also do current measurements using an ADCP. Guess I’d better explain what that is as well. An Acoustic Doppler Current Profiler uses a physical phenomenon called Doppler shift to measure how fast water is flowing. When a sound wave is reflected from something that moves, the frequency of the sound will shift slightly. You can observe this when an ambulance drives past you, the sound changes when the ambulance passes the point where you are standing. This shift in frequency is what an ADCP uses to calculate current profiles.
As the CTD is performed in deep waters (2700m) it takes about 1,5 hours to get to the bottom and a bit more to get back up.
To be continued….
Espen R. Mikkelsen
Institute of Marine Research, Norway
20 July 2007