Diary / Dagboek

R/V Pelagia Cruise ARCH-OCEAN

Monday, 14 January 2008
End of an exciting voyage... Our voyage comes to an end. There are only two days left before we’ll disembark at Las Palmas, Canary Islands. During these final days we are busy with finishing up some experiments and stowing instruments and equipment back into their boxes. The lots of water samples and filter-samples to determine microbial diversity will be stored in the fridges and freezers to be taken off the RV Pelagia once she is back at the NIOZ harbor. She is expected to be back home at the NIOZ by 28 January. Thus, while we go off the ship at Las Palmas, the ship’s crew has still at least more than one week of sailing ahead and the weather conditions further north are certainly less pleasant than here in the southern part of the North Atlantic. The evening meetings are now not any more on ‘what to sample next day’ but are presentation of data collected during the cruise. So did this research cruise shed new light on the dark ocean? Did we advance our understanding of the deep North Atlantic and the microbes being the main drivers of the biogeochemical cycles in the ocean? The answer to this question is certainly: yes, we did! The Romanche Fracture Zone with the Vema-Deep as the deepest spot of the Atlantic turned out to have some specific features in terms of biogeochemistry and microbial oceanography. We could find some higher dissolved organic matter concentrations in the deeper layers than in the layers between 2000-3000 m depth. These elevated concentrations of dissolved organic matter might originate from the steep slopes of this fracture zone in the Mid Atlantic Ridge. Another exciting finding is that most the bacterial extracellular enzymes are actually not bound to the cell surface but rather dissolved, freely floating in the water. In these nutrient deserts of the deep ocean one might think that this is not a wise strategy for these bacteria to release their precious hydrolytic exoenzymes into the ambient water instead of keeping them at the cell surface to increase the chance that when a potential substrate molecule is cleaved that the cleavage product can also be taken up – known as a close hydrolysis-uptake coupling. The dominance of freely dissolved bacterial enzymes in the deep ocean suggests that most of these deep-water bacteria might actually be attached to some fragile colloidal material which becomes disrupted during sampling with our sampling rosette and the turbulence we generate with it. We have also found evidence using camera systems mounted on the CTD frame that there are a lot of mm-sized particles throughout the water column, not only close to the sunlit surface waters, as one might suggest, but also in the really deep waters. Further in-depth analyses will reveal whether there is really a predominating particle-attached microbial community in the deep ocean. As it is now, this is an exciting idea, which needs some thorough analyses of the data we have collected. After sailing now more than five months in the North Atlantic on five cruises in total focusing on the deep water microbial oceanography from the Polar Circle to 5°S in both the western and the eastern basin of the North Atlantic, it is obvious that there is substantial heterogeneity in the deep water microbial activity. The work has not finished though with our return to home. In the home labs of the different participants, we will be busy in extracting nucleic acids for diversity studies and linking diversity and metabolic activity to the hydrography of the deep North Atlantic. This will take us about one more year until will eventually have a more definitive answer. During the cruise we have revised some of our original hypotheses – this is what makes science so exciting. A successful cruise, like the one we are just about to complete, is depending not on a single person but is truly a team effort, both from the scientific and the ship’s crew. Each of us had a specific role in this team over the past four weeks. We have developed some routine in it over this time and besides that, we had a lot of fun as well. Each one of the team was contributed an essential part to the success of this voyage. Thanks to those who contributed to the exciting research expedition on the ship, back in the several research institutes involved and finally, to the families who had to celebrate Christmas and New Year’s Eve without us and hence, at least tolerated our absence from home. Gerhard J. Herndl Chief-Scientist