Award: OCE-1559198

Miles beneath the oceans surface in the dark abyss, vast communities of microbes at deep-sea hydrothermal vents are converting chemicals into energy in a process known as chemosynthesis - the production of living cells from carbon dioxide (CO2) by using chemical energy rather than light as in photosynthesis - that allows deep-sea life to thrive in a world without sunlight - part of Earths rich tapestry of life in the most surprising places. Yet, there is currently a lack of studies measuring rates of chemosynthetic carbon fixation in situ, i.e., directly at the seafloor, which is a measurement ultimately needed to constrain production in these ecosystems. To this end, we have developed the Vent-Submersible Incubation Device (Vent-SID), a robotic micro-laboratory that makes it possible for the first time to determine rates of carbon fixation directly at the seafloor and at the temperature of the vent fluids at diffuse-flow deep-sea hydrothermal vents. This is made possible by the novel capability of controlling the temperature of the twin incubation chambers, which mimic the physical conditions within warm water hydrothermal vent fluids being sampled at the sea floor and which likely exist deeper below the seafloor. In addition, the Vent-SID chemically preserves incubated samples at the time of subsample acquisition in a manner compatible with the latest molecular techniques for assessing the biochemical pathways utilized by the microbes. A cruise with R/V Atlantis/HOV Alvin took place in May 2017 to the 9oN hydrothermal vent field on the East Pacific Rise (AT37-12). During the cruise, a total of three deployments took place. While the instrument worked as expected during test runs performed on deck, the deployment and recovery of the Vent-SID went very well, and no issues were encountered, we were unfortunately not able to get a successful seafloor deployment. In the end, it turned out that the stalling of the piston in the incubation chamber at in situ pressure had caused the instrument to fail to execute the program. To demonstrate proof of concept, we performed shipboard incubations using vent fluids collected by major titanium water samplers. In total, we conducted 6 on-deck incubation experiments to simulate a sea-floor incubation of the Vent-SID. The six 6-hour long incubations were all carried out at ~25oC, the temperature of the vent fluids. Overall, the results of these shipboard incubations show that the incubations worked as envisioned, validating our approach. In the meantime, we have fixed the issue that occurred during the cruise and have performed successful tests at WHOIs pressure test facility showing that the chambers function at the pressure of the studied vent sites. This makes us confident that we will be able to perform seafloor incubations under in situ conditions. The Vent-SID is a very exciting piece of equipment that has the potential to revolutionize the way we conduct microbial biogeochemical investigations at deep-sea hydrothermal vents. Broader Impacts. The project implemented education and outreach efforts at multiple levels. The project involved the participation of undergraduate and graduate students, resulting in one PhD thesis. For the cruise, a blog site was set up (Dark Life II; https://web.whoi.edu/darklife/) to educate and inform a broad audience about our research and related activities, including reports by 11 first-time divers in Alvin. Sievert worked with teacher Lisa Troy and academic dean Dr. Nitzan Resnik of The Sage School on an Engineering Design Challenge related the Vent-SID for a 6th grade class. As part of the project, the students had to design, build, and test a sampling chamber using the design and engineering process. Along the way, they learned about the discovery of deep-sea vents and the functioning of the ecosystem, the role of microorganisms, challenges to conduct research and measurements in the deep-ocean, difference between heat and temperature, heat transfer, and the effects of pressure. This project was described in a manuscript entitled Engineering Partnerships: How collaborating with a scientist created an authentic engineering problem that was published at Science Scope (Troy et al., 2018, 41 (8); https://www.jstor.org/stable/44843339), a journal by the National Science Teachers Association for middle and high school science teachers. An adaptation of an article reporting on the productivity of the deep-sea vent subseafloor biosphere (McNichol et al., 2018, PNAS, 115:6756-6761) was produced for the Environmental Science Journal for Kids (https://www.sciencejournalforkids.org/search-articles/how-do-deep-sea-hot-spring-ecosystems-work). Project members further presented their work in many talks, both at scientific conferences and in talks geared towards the public. The project also provided opportunities for professional development, in particular to a number of early career scientists who were invited and provided an opportunity to collect samples for their own research and to be part of the daily science planning activities on board the ship. The cruise further provided opportunities for two postdocs and four graduate students, who all got their first dive in Alvin. Last Modified: 11/24/2020 Submitted by: Stefan M Sievert