Introduction

Participants

 

R/V Pelagia Cruise GLOW
	Diary overview
Friday, 20 February
We spent the last three days surveying the area for potential coring targets, and for understanding the regional geology of the area. Towards the end of the S-N Davie ridge line, that we sailed on the 16th of February, the energy of the returning sound waves became too weak to continue. The technicians have done their utmost best to service the new airgun and the streamer, but to no avail. These painful things happen during cruises, we waited patiently. During the test of the serviced equipment, not even the weakest signal could be detected on the recorder. This was really a shame, the new airgun failed completely to produce a signal. But not deterred, the old airguns were deployed, and immediately the recorders were rattling. Sitting in the seismic lab is a remarkable experience listening to the sound, a loud initial bang of the airgun is followed by nice popping sounds of the returning waves.   The second line towards the Tanzanian coast delivered a classic picture of the basin followed by the continental rise and slope. We certainly sailed a beautiful Pleistocene upper slope sequence with nice reflectors, but no mass wasting. We aim to use this line later for coring along a depth transect to favor late Pleistocene paleoceanography. The next line was really crucial for us to get a glimpse of the regional geology. We sailed a line obliquely across the GLOW area from the NW corner all the way through to the SE corner where we started on Davie Ridge. The line became a geological delight, we went down the slope into the basin, where suddenly another ridge appeared, the so called Sea Gap area. This ridge gave us what we wanted, slivers of crust covered with sediments of unknown age, but certainly hope for us to find older sediments exposed. We even saw the potential of old reefs on some of the slivers. This area clearly suffered from strike-slip faulting, producing a kind of flower structure. After the ridge, we plunged again in the deep ocean, with hummocky surface terrain characteristic of a typical turbidite field. Finally, the second deep basin was followed by the Davie Ridge structure, again at the flank of the ridge, an area of massive strike-slip faulting with almost vertical faults. Now the seismic equipment was working so well, we decided to rerun the first line, because Davie Ridge is crucial, providing potential drilling targets. The new line and multi-beam results are absolutely fantastic, remarkable detailed structures can be read. Deep-sea canyons on top of the ridge were discovered 400-500 meter deep. It is hot out here, way above thirty degrees. Inside the ship, airconditioning cools the interior. This helps us to cool down, helped by a nice can of cool beer. Some of us spent hours in a small self made swimming pool by the ship crew, absolutely marvelous. The sailors are very brave to endure the heat for long hours on deck, painting. They deserve a golden medal. They certainly have the biggest tan so far, although some of the scientists do their best to keep up with them.   Just a few hours ago, the first box-core came on deck. We aimed to date the sediment sequence (for calibration with the seismic line) on top of Davie Ridge by sampling a canyon profile. The first core gave a Pleistocene age on top of the ridge. The second, 300m into the slope of the canyon, delivered a debris flow with a minimal age of 6 million years. Now, we are going to make an attempt to sample the sediments deep in the canyon. Hopefully, the sediments are even older as we are hunting places for drilling Paleogene sediments. We will report.   The shipboard party