We have had a number of very productive dives so far, bringing back treasures from the abyss for the scientists to work on. On the so-called basket in front of Alvin, we have fluid samplers made out of titanium to collect the hydrothermal fluids of both warm and hot vents, and so-called bioboxes to bring back animals, like Riftia, crabs, and mussels, as well to bring down and recover experiments. We put them in the biobox to shield them from being affected by the ambient seawater during descent and ascent. In addition, the bioboxes keep the temperature of the deep-ocean water, which is around 2ºC or 35ºF, while the sub is bathing in 30ºC (86ºF) warm surface ocean water during recovery of Alvin. Keeping the animals cold helps to alleviate the effect of reduced pressure that the animals are faced with during ascend. On this cruise, we also have used baited Crab Traps, similar to what is being used in the coastal ocean. More on this from Carolyn in a later post.
But today, I would like to draw the attention to another instrument that we have relied on heavily over the last 10 years. Its name is unassumingly the Large Volume Pump or LVP for short. Its name suggests what it does. It basically allows us to filter large amounts of vent fluids, in the range of a few hundred liters, directly at the seafloor. We have started using the LVP on a cruise in June 2006, when we were sampling at 9N EPR in the aftermath of a volcanic eruption that had occurred there in late 2005/early 2006. The LVP is originally designed to filter large volumes of seawater in the water column, but we outfitted it with a hose and a nozzle to be able to sample hydrothermal fluids emitted through cracks and orifices at the seafloor. The fluids are then pumped through a very fine filter (the pore size is 1/5000 of a millimeter or 0.2 micrometer), which allows us to ‘catch’ bacteria and other microbes contained in the vent fluids on the filter directly at the seafloor. Over the years, the LVP has not disappointed us, reliable returning precious samples for subsequent analysis aimed to better understand the diversity and function of the microbial communities that form the basis of deep-sea vent ecosystems.
Using the large number of cells that are collected on the filter (each liter of vent fluid contains around 300 million bacteria, compared with about 10 million in one liter of ambient deep ocean water). So, the vents are a hot spot for microbial life, providing the food for the lush animal communities we find there.
Back in the lab, we extract and analyze the DNA, RNA, proteins, and lipids of the microbes collected on the filters, which then informs us about the types of microbes, their metabolism, i.e., what they do for a living, and their adaptations allowing them to live under the extreme conditions found at the vents.
Tonight we are deploying the LVP for a second time. It will be put in position at Teddy Bear by Alvin tomorrow and released first thing on the dive the day after tomorrow. For the recovery of the LVP from the seafloor, Alvin is pulling a pin, releasing the weight stack that initially brought the pump to the seafloor. Using flotation in the form of 12 vacuumized glass spheres on top, the LVP will then rise quickly to the surface, where we will pick it up and expeditiously process the filter.