An apparatus is being developed for sampling water for signs of microbial life in an ocean hydrothermal vent at a depth of as much as 6.5 km. Heretofore, evidence of microbial life in deep-sea hydrothermal vents has been elusive and difficult to validate. Because of the extreme conditions in these environments (high pressures and temperatures often in excess of 300°C), deep-sea hydrothermal- vent samplers must be robust. Because of the presumed low density of biomass of these environments, samplers must be capable of collecting water samples of significant volume. It is also essential to prevent contamination of samples by microbes entrained from surrounding waters. Prior to the development of the present apparatus, no sampling device was capable of satisfying these requirements.
The apparatus (see figure) includes an intake equipped with a temperature probe, plus several other temperature probes located away from the intake. The readings from the temperature probes are utilized in conjunction with readings from flowmeters to determine the position of the intake relative to the hydrothermal plume and, thereby, to position the intake to sample directly from the plume. Because it is necessary to collect large samples of water in order to obtain sufficient microbial biomass but it is not practical to retain all the water from the samples, four filter arrays are used to concentrate the microbial biomass (which is assumed to consist of particles larger than 0.2 μm) into smaller volumes. The apparatus can collect multiple samples per dive and is designed to process a total volume of 10 L of vent fluid, of which most passes through the filters, leaving a total possibly-microbe-containing sample volume of 200 mL remaining in filters.
A rigid titanium nose at the intake is used for cooling the sample water before it enters a flexible inlet hose connected to a pump. As the water passes through the titanium nose, it must be cooled to a temperature that is above a mineral-precipitation temperature of 100°C but below the upper working temperature (230°C) of switching valves and tubes in the apparatus. The sample water then passes into a manifold tube, from whence the switching valves can direct the water through either a bypass tube or any one of the filter arrays, without contamination from a previous sample. Each filter array consists of series of filters having pore sizes decreasing in the direction of flow: 90-, 60-, 15-, and 7-μm prefilters and a large-surface-area 0.2-μm collection filter. All the filter taps are located between the intake and the bypass tube so that each time the bypass tube is used, the entire manifold tube is flushed as well.
The switching valves include five passive ones (a check valve for the bypass tube for each of four filter arrays) at the upstream (manifold) end and an active one (a five-position actuated valve) at the downstream end. The incorporation of the check valves at the upstream end makes it unnecessary to use actuated valves at both ends. Once the actuated valve has been turned to the bypass position, the pump begins to flush the intake and manifold of any particulate matter that may have accumulated. After flushing, sampling is started by setting the actuated valve to pass water through one of the filter arrays. The process of flushing and sampling is repeated for each of the four filter arrays.
Because the apparatus is rated to a depth of 6.5 km, it is pressure-compensated; as the pressure increases between atmospheric at the ocean surface and about 10 kpsi (≈69 MPa) at maximum depth, the volume of water within the system decreases by about 2.7 percent. A flexible membrane within the apparatus accommodates the compression and expansion of water upon descent and ascent, respectively.
The apparatus includes a system for monitoring and regulating temperatures, pressures, and flow rates throughout the system. This control and monitoring system includes a small micro-processor, motor controllers (for the pump and the valve actuator), the aforementioned temperature probes, pressure sensors, and a serial data link to a laptop computer aboard a submarine or other vessel used to bring the apparatus to and from the hydrothermal vent.
This work was done by Alberto E. Behar, Kasthuri Venkateswaran, and Jaret B. Matthews of Caltech; Cesar Rivadeneyra, James C. Bruckner, Edmond So, and Goran Basic of the International Space University; and Jonas Jonsson of Uppsala University for NASA’s Jet Propulsion Laboratory.
NPO-42617
This Brief includes a Technical Support Package (TSP).
Deep-Sea Hydrothermal-Vent Sampler
(reference NPO-42617) is currently available for download from the TSP library.
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Overview
The document discusses the development of a novel hydrothermal vent biosampler (HVB) designed by NASA's Jet Propulsion Laboratory (JPL) to collect pristine samples of hydrothermal fluids from extreme deep-sea environments. These habitats, often exceeding temperatures of 300°C, present significant challenges for sampling due to their harsh conditions and the low biomass of microbial life present.
The HVB is engineered to withstand temperatures up to 400°C and has been pressure-tested to simulate depths of 6.5 kilometers, making it suitable for deep-sea exploration. The sampler incorporates in-situ sensing devices to monitor real-time temperature and flow rates, ensuring that samples are collected from specific areas of interest without contamination from surrounding waters. This is crucial, as the quality of the samples directly impacts the validity of the scientific analyses performed on them.
To address the challenge of low biomass in these environments, the HVB employs a series of pre-filters with pore sizes of 90, 60, 15, and 7 μm, along with a large surface area collection filter of 0.2 μm. This filtration system allows the sampler to concentrate 10 liters of fluid into a final sample volume of approximately 200 milliliters, enabling the collection of multiple samples during a single dive.
The document also details the operational mechanics of the HVB, including a rigid titanium nose that cools the vent fluid before it enters the system, and a manifold tube that allows for contamination-free sampling from various filter arrays. The system is equipped with a control and monitoring setup that regulates temperatures, pressures, and flow rates, ensuring optimal performance during sampling.
The ultimate goal of the HVB is to enhance our understanding of the unique biota associated with hydrothermal systems, which are often composed of chemosynthetic microorganisms. The document emphasizes the importance of collecting uncontaminated samples to validate the presence of microbial life within hydrothermal plumes, which has historically been difficult to confirm.
In summary, the HVB represents a significant advancement in deep-sea sampling technology, aimed at uncovering the mysteries of hydrothermal ecosystems and contributing to our knowledge of life in extreme environments.
