Nov. 20: Alvin Dive 4994

On this expedition, R/V Atlantis continues the tradition of sailing an expedition artist: Rebecca Rutstein from Philadelphia. In contrast to her 18th century predecessors, her specialty is not rendering naval battles of Her Majesty’s fleet with sails billowing and cannon blasting over foam-flecked waves, but semi-abstract seascapes in motion, overlaid with elements from technical drawings and plots, for example bathymetric 3-D maps, or microbial shapes and outlines that superimpose a technical or a biomorphic lineament on the complex, animated background. This multi-layered effect can be achieved on paper, but also in mixed media that range all the way to very large installations with built-in light sources.

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Rebecca is diving with Mandy, who is deploying osmosamplers, fluid sampling devices driven by the dissipation of a concentration gradient that suck sediment porewater into thin, long tubes at a very slow rate. In this way, it is possible to obtain a continuous long-term record of porewater chemistry over multiple days, weeks and even months. Todays dive target for osmotic and artistic inspiration is Cathedral Hill. Also, there will be cores…

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A special feature of this dive is the use of an elevator, a landing platform that carries instruments to the seafloor that would be too bulky to carry on Alvin’s sampling basket. Here, Alvin recovers the four osmosamplers for deployment at a promising hydrothermal hot spot. The indate port of the Osmosampler [right] is placed into the sediment together with an adjacent temperature logger [left], equipped with five integrated temperature recorders that are spaced 10 cm apart, courtesy of Howard Mendlovitz at the Martens Geochemistry lab in UNC-Chapel Hill. The T-loggers automatically record the in-situ temperature every ten minutes over two weeks, or, until the last Alvin dive when the instruments are recovered. In this way, it will be possible to correlate the chemistry of the sediment porewater that the osmosampler is taking up, with the in-situ temperature regime.

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These deployments take place in the breathtaking hydrothermal landscape of the Cathedral Hill region, easily our favorite during this expedition. Here, a small spire adjacent to the instrumented hydrothermal area is overgrown by two coexisting species of tube worms, the larger Riftia and the smaller Paralvinella; these in turn are embedded in a soft pillow of yellow and orange Beggiatoaceae.  Normally, sulfur-oxidizing filamentous bacteria grow at a narrow interface, where sulfide and a suitable oxidant [oxygen or nitrate] meet; but thick pillow-like accumulations require turbulent mixing of sulfidic vent water and oxidant. The tube worms have the same habitat requirement, since they sustain their internal sulfur-oxidizing symbionts with sulfide and oxygen [plus CO2 as carbon source] that is taken up through their gills.

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The dive team returns with many sediment cores and tubeworm specimens, and – we are quite certain – lots of artistic inspiration !

 

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