Award: OCE-1061827

The extensive deep-sea biosphere hosts a variety of habitats where chemical transformations and microbial processes take place. Beneath the sediments of the seafloor, and especially on the flanks of the worldwide mid-ocean ridge system, lies fractured and permeable volcanic rock crust with circulating fluids. This æsubseafloorÆ biosphere hosts a huge range of temperature, pH, and chemical conditions that have only begun to be explored over the last two decades. Understanding which, how much, and how chemicals cycle between the deep ocean and the subseafloor is important for understanding how our Earth-ocean-atmosphere system works, and understanding what role microbes play in these processes is important to understanding how life on Earth functions. This project targeted North Pond, an isolated sediment pond on 7-8 million year old seafloor on the flanks of the Mid-Atlantic Ridge, and made comparisons with other sites where subseafloor samples have been available. This specific project was part of a large international collaboration between marine scientists specializing in physics, geology, chemistry, and microbiology. During two research expeditions using ROV Jason-II to visit sites in the mid-Atlantic where the Integrated Ocean Drilling Program previously drilled the seafloor and installed CORK Borehole Observatories, custom instruments and sensors were used to collect data and pristine fluid samples from as deep as 335 meters below the seafloor. Sensor data, fluids, and particles collected during this project have been used for chemical and microbiological analyses and experiments to elucidate the relationship between fluid chemistry, microbial communities, and the transport of energy and nutrients. The North Pond site hosts a very hydrologically-active subsurface aquifer that represents early stages of alteration as bottom seawater percolates into the subsurface. Subsurface fluids contain a large amount of oxygen, but also host particulate iron of mixed oxidation states, indicating reactions with the basalt rock. The data from the North Pond CORK Observatories represent an excellent contrast to previous and on-going studies made at the Juan de Fuca Ridge Flanks in the Pacific Northwest, and help to further our understanding of differing provinces, or habitats, in the deep ocean. Last Modified: 07/13/2015 Submitted by: Brian T Glazer