Abstract
AbstractThe investigation of benthic biodiversity and biogeochemical processes in the deep sea is complicated by the need to conduct experiments at in situ pressures. Recovery of sediment samples to the surface without maintaining full-depth ambient pressure may damage the organisms that are of interest or cause physiological changes that could influence the processes being studied. It is possible to carry out in situ experiments using remotely operated vehicles (ROVs) or lander systems. However, the costs and complexity of ROV operations are significant and, for both ROVs and landers, the complexity and repeatability of the experiments are subject to the limitations imposed by these platforms. A system is described—the Multi-Autoclave Corer Experiment (MAC-EXP)—that has been developed with the aim of offering a new experimental approach to investigators. The MAC-EXP system is designed to retrieve sediment cores from depths down to 3500 m and to seal them into pressure chambers before being recovered so that they are maintained at their normal ambient pressure. After recovery the core chambers can be connected to a laboratory incubation system that allows for experimentation on the sediment without loss of pressure and under controlled conditions of temperature and oxygen concentration. The system is relatively low cost when compared to ROV systems and can be deployed using methods and equipment similar to those used for routine deployments of small unpressurized multicorers. The results of sea trials are detailed.
Highlights
Most of Earth’s solid surface is deep seafloor lying at depths of more than 200 m, with 70% at a pressure of 38 MPa or above
The gill design followed that of similar systems (Morse et al 1999; Sommer et al 2008) but differs in that these systems were designed to work on the seabed during deployment, whereas for the Multi-Autoclave Corer Experiment (MAC-EXP) system the gill operates under pressure but at the surface after recovery of the cores
The corer system was tested on a 3-week cruise aboard the British Royal Research Ship (RSS) Discovery in the spring of 2016 in the North Atlantic areas of Goban Spur and Rockall Trough
Summary
Most of Earth’s solid surface is deep seafloor lying at depths of more than 200 m, with 70% at a pressure of 38 MPa or above. Marine sediments are a major reservoir in the global carbon cycle, and the formation, cycling, or burial of organic matter (OM) in marine sediments are key processes in the global carbon, nitrogen, and phosphorous cycles. While its remoteness and inaccessibility renders the deep ocean the least known ecosystem on Earth, they are increasingly at the forefront of human resource exploration. Prokaryotes usually dominate benthic biomass in deep-sea sediments, and are regarded as the primary agents of OM demineralization, but to date our knowledge of the ecology of deep-sea organisms and deep-sea food webs is very limited and information is scarce with regard to prokaryote diversity and ecosystem function.
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