28/29 June

R/V Pelagia Cruise HERMES

Wednesday-Thursday, 28-29 June ‘06	Top of the CTD-frame
Finally we got some "good CTD weather" on this cruise! The Conductivity-Temperature-Depth (CTD) probe is the trusted workhorse of oceanography. It can usually be deployed even in bad weather, when other operations are cancelled because they become impractical or unsafe. So the first week we were out here, when the weather was so uncharacteristically nice - we hardly recognized the place when the sky was blue and the sea flat - we made the most of it by getting all the other gear: box cores, dredges and camera systems and so on (see previous diary entries) in and out of the water to our hearts' content. Then, when the weather turned a bit more like what we remembered and expected of the Rockall area, it became time for the "CTD team" to spring into action...
On Wednesday we did a "yo-yo" station, staying in one location and repeatedly letting the CTD go down to near the seabed and back up to the surface. All the time it's measuring the temperature, salinity, oxygen concentration, optical backscatter (a measure of the amount of particles in the water) and fluorescence (a measure of the chlorophyll concentration). We could see quite some changes in the water column over the about seven hours of yo-yoing, for example how cold, slightly fresher and more oxygen-rich water from the deep was lifted up by the tide. The strong tidal currents in the area are important to the corals, both for the food supply and because of the effect they have on the sedimentation. After a CTD transect across the mound on Thursday, Friday afternoon and evening was dedicated to another yo-yo station, this time for twelve hours near the top of a seamound. With all the CTD profiles and the different landers and moorings, we're building up a nice collection of data which will help us to better understand the flow of water around these mounds and how it affects the mounds themselves and the corals. In the midst of the hydrographic work, we also found time to crown the King of the Multibeam. There's some competition for the title as a few people take turns wrestling with the mapping software and they have all claimed different partial victories. But still, only a real computer whizkid can get to wear the royal crown made (by Furu) out of CTD logsheets and yellow plastic tape. All hail King Andy! Jenny Ullgren National University of Ireland