A Pressure-Tight Sampler with Flexible Titanium Bag for Deep-Sea Hydrothermal Fluid Samples
1. Introduction
Owing to its unique mineralization system, ecosystem, and its contribution to the heat and material of the ocean, seafloor hydrothermal activity, which is generally developed along the midocean ridges, has become a popular topic of research in many academic fields in the past decades. The organic carbon cycle in the deep-sea hydrothermal system is an essential part of the oceanic organic carbon cycle, and it may have important implications for developing our understanding of the origin and evolution of life on Earth (Daniel et al. 2006; Martin et al. 2008; Konn et al. 2009; Lang et al. 2010; Edwards 2011; Hawkes et al. 2016). In recent years, more and more attention has been paid to the organic chemistry of hydrothermal systems (Konn et al. 2012; Reeves et al. 2014; Rossel et al. 2015; Yang et al. 2017; Rossel et al. 2017; Lang et al. 2018).
Collecting hydrothermal fluids with suitable samplers and then analyzing its organic composition in the laboratory has always been an effective means of studying the organic chemistry of hydrothermal fluids. In the past few decades, a variety of samplers have been designed and constructed to collect fluid samples from hydrothermal vents. These devices can be generally divided into two kinds: 1) syringe-type samplers, such as the “major” sampler (Von Damm et al. 1985; Butterfield et al. 1990), the isobaric gas-tight sampler (Seewald et al. 2002; Proskurowski et al. 2008; McDermott et al. 2015), and the handheld sampler for collecting organic samples from shallow hydrothermal vents (Wu et al. 2013); 2) pumped flow-through samplers, such as the Hydrothermal Fluid and Particle Sampler (HFPS) (Huber et al. 2002; Butterfield et al. 2004; Lang et al. 2006), the Peristaltic Organic Pump sampler (POP gun) (McCollom et al. 2015), and the Kiel Pumping System (KIPS) (Garbe-Schönberg et al. 2006; Schmidt et al. 2007). Among these samplers, the “major” sampler is not well suited for analyzing the volatile and semivolatile species of the hydrothermal fluids due to its non-gas-tight characteristic. The handheld sampler can only be used in shallow water. The three pumped flow-through samplers cannot be used to collect pressure-maintaining fluid samples. Only the isobaric gas-tight sampler can maintain the fluid samples at near seafloor pressure by using compressed nitrogen gas. Therefore, the hydrothermal samples collected by this kind of sampler can be used not only for analysis of dissolved organic matter but also for a quantitative analysis of dissolved gas components without degassing. However, the isobaric gas-tight sampler is sealed with O-rings. A certain amount of silicone grease should be applied on the O-rings for lubrication, but this is an easy way to introduce organic pollutants during the sampler assembly process, resulting in sample contamination (McCollom et al. 2015).
A sampler with a metal seal has been designed and constructed to address these issues. This sampler uses a flexible titanium foil bag to store the hydrothermal fluid and a customized titanium diaphragm valve for sampling. A key feature of this new sampler is that all components in contact with the hydrothermal fluid are made of pure titanium or titanium alloy. It means that the O-rings or other plastic materials will not limit the maximum operating temperature of this sampler. More importantly, the sampling valve and the titanium foil bag can be heated in a high-temperature furnace after assembly to eliminate organic contamination that may be introduced during the assembly process. Furthermore, this sampler can maintain the sample pressure near to that on the seafloor and regulate the fill rate of the fluid samples.
2. Structure and working principle of the sampler
This sampler is designed for a maximum working depth of 4500 m, as the depth of most known hydrothermal vents is within this range (Baker and German 2004). As shown in Fig. 1, the sampler mainly consists of 1) an accumulator chamber with a piston inside; 2) a sample chamber with a flexible titanium foil bag inside; and 3) a custom-made, titanium diaphragm sampling valve coupled with an actuator and control circuit chamber. The accumulator chamber is placed at the uppermost end of the frame, away from the inlet snorkel, to avoid being heated by the hot hydrothermal fluid during the sampling process. Without the snorkel and handle attached, this instrument is 43 cm long and 32 cm high. It weighs approximately 15 kg in air and 10 kg in seawater. The sample volume is approximately 140 mL. Before deployment, the accumulator piston is positioned against the bottom of the accumulator chamber, and the titanium foil bag is in a flattened state (Fig. 2a). The dead volume in the flexible titanium foil bag and the snorkel is filled with sterilized bottom seawater, while the sample chamber can be filled with deionized water or tap water as it will not come into direct contact with the hydrothermal sample. Meanwhile, the accumulator chamber is prefilled with nitrogen gas to an appropriate pressure value for the deployment depth. When the sampling valve is triggered to open on the seafloor, the high pressure sample fluid gradually flows into the sampler and inflates the flexible titanium foil bag. Then the deionized water in the sample chamber is squeezed into the accumulator chamber through the orifice (Fig. 2b). The nitrogen gas in the accumulator chamber will be further compressed until it reaches pressure balance. During this process, the fill rate of the fluid sample is regulated by the orifice inside the bottom cap, which restricts the flow of the deionized water into the accumulator chamber. The fluid sample is sealed inside the titanium foil bag when the sampling valve is closed. Since the titanium foil bag is flexible, the difference of pressure inside and outside the bag is minimal. The pressure of the fluid sample is almost equilibrated with the pressure of the compressed nitrogen gas. So, a pressure-maintained fluid sample can be obtained after the sampler is recovered.
Structure of the pressure-tight sampler.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Structure of the pressure-tight sampler.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Structure of the pressure-tight sampler.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Schematic illustration of the sampling and pressure-maintaining process: (a) before sampling and (b) after sampling.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Schematic illustration of the sampling and pressure-maintaining process: (a) before sampling and (b) after sampling.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Schematic illustration of the sampling and pressure-maintaining process: (a) before sampling and (b) after sampling.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
3. Titanium diaphragm sampling valve
a. Structure and working principle
As mentioned above, all parts of the sampling valve in contact with the fluid sample should be made of chemically inert and high-temperature-tolerant materials such as pure titanium or a titanium alloy to collect a high-purity fluid sample without contamination. As one of the most critical components of the sampler, the sampling valve should also have bidirectional sealing capability under high pressure to ensure sampling success. Therefore, a cone seal sampling valve, all components of which are made of titanium material, was designed. As shown in Fig. 3a, it mainly consists of a pushpin, titanium diaphragm, valve poppet, return spring, and valve seat. The pushpin and the poppet are separated by the titanium diaphragm, which is welded onto the diaphragm seat. A cone seal between the diaphragm seat and the valve seat ensures sealing as the cap screws down. The titanium diaphragm has a certain flexibility to allow the pushpin and the poppet small movement in the axial direction. When the sampling valve is closing, the pushpin pushes the poppet down through the titanium diaphragm; then, a cone seal is formed between the poppet and the valve seat. Conversely, when the valve is opening, the pushpin moves up, then the poppet moves up under the action of the return spring, and then the fluid sample flows into the sampler (Fig. 3b). Since both sides of the diaphragm are subject to high pressure during the sampling process, the diaphragm does not withstand extra hydraulic force.
Structure and sampling process of the titanium diaphragm sampling valve: (a) close status and (b) open status.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Structure and sampling process of the titanium diaphragm sampling valve: (a) close status and (b) open status.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Structure and sampling process of the titanium diaphragm sampling valve: (a) close status and (b) open status.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
b. Stress analysis
Compared with titanium alloy, pure titanium is more flexible, so we chose pure titanium (grade 2) as the material for the diaphragm. The diaphragm used here is a convex diaphragm with a diameter of 20 mm and a thickness of 0.1 mm. The diameter of the pushpin and poppet are 6 and 4 mm, respectively. A 3D finite element (FE) model based on the diaphragm’s structure was developed to analyze the stress distribution of the diaphragm by using ANSYS software. The geometry of the FE model is shown in Fig. 4.
FE model of the titanium diaphragm.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
FE model of the titanium diaphragm.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
FE model of the titanium diaphragm.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Material nonlinearity, geometric nonlinearity, and contact nonlinearity were considered during finite element analysis (FEA). The stress–strain relationship of pure titanium (grade 2) is shown in Fig. 5, which comes from the material supplier. The maximum axial displacement of the poppet was set to be 1.5 mm during application. Therefore, the displacement loads to the diaphragm were incrementally applied up to the same magnitude. As shown in Fig. 6, the maximum von Mises equivalent stress (SEQV) of the diaphragm is 391 MPa, which is greater than the yield point (345 MPa) but less than the tensile strength (485 MPa) of pure titanium. It indicates that the diaphragm will undergo plastic deformation but will not rupture. Also, the relationship between the von Mises SEQV and the radical position is drawn according to the FEA data, which indicates that the von Mises SEQV on the conjunction of the pushpin and the diaphragm is big and the maximum value appears on the edge of the diaphragm (Fig. 7).
The stress–strain curve of pure titanium (grade 2).
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
The stress–strain curve of pure titanium (grade 2).
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
The stress–strain curve of pure titanium (grade 2).
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Von Mises SEQV distribution of titanium diaphragm.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Von Mises SEQV distribution of titanium diaphragm.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Von Mises SEQV distribution of titanium diaphragm.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Relationship between the von Mises SEQV and radial position according to the FEA results.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Relationship between the von Mises SEQV and radial position according to the FEA results.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Relationship between the von Mises SEQV and radial position according to the FEA results.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
c. Endurance test
As the most vulnerable part of the entire sampling valve, the titanium diaphragm determines the life of the sampling valve to a great extent. After switching the sampling valve multiple times, the diaphragm is prone to fatigue damage, resulting in failure of the sampling valve. A titanium diaphragm should be able to withstand at least 100 sampling processes without being damaged, considering its practicality and testability. Therefore, an experiment was carried out to verify the endurance life of the titanium diaphragm. As shown in Fig. 8a, software developed using LabVIEW (on a laptop) was used to control the valve automatically. After the automatic switching process, the valve was immersed in the water and charged with 0.3 MPa nitrogen gas through the inlet to check if the diaphragm was broken (Fig. 8b). If the titanium diaphragm ruptured during the test, the air bubble would go into the water, which can be observed. Finally, after the test, the diaphragm had a visible plastic deformation but still did not rupture (Fig. 9). The fatigue test was repeated many times in the laboratory to make the test results more credible, and the results show that the titanium diaphragm meets the requirement.
(a) Switching the sampling valve automatically. (b) Putting the valve into water with 0.3 MPa N2 charged through the inlet to check if the diaphragm is broken.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
(a) Switching the sampling valve automatically. (b) Putting the valve into water with 0.3 MPa N2 charged through the inlet to check if the diaphragm is broken.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
(a) Switching the sampling valve automatically. (b) Putting the valve into water with 0.3 MPa N2 charged through the inlet to check if the diaphragm is broken.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
The different status of the titanium diaphragm (a) before the test and (b) after the test.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
The different status of the titanium diaphragm (a) before the test and (b) after the test.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
The different status of the titanium diaphragm (a) before the test and (b) after the test.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
4. Titanium foil bag
a. Structure design and construction
As Fig. 10 shows, the titanium foil bag is composed of a head, a foil body, and a bottom with a plug, which are all constructed from pure titanium (grade 2) and permanently welded together. Both the head and bottom parts are wedge shaped, which minimizes the dead volume of the titanium foil bag and guides the deformation of the flexible foil body to prolong its endurance. The perpendicular through-hole in the head, close to the transverse welding line, is designed to drain the water in the gap between the foil body and head. The thinner the titanium foil is, the better flexibility it has; however, this makes it difficult to construct the titanium foil bag. The compromised thickness value of the foil body was set at 0.1 mm, considering the flexibility and welding difficulty (Wu et al. 2016). The volume of the flexible titanium foil bag is 160 mL.
Structure of the flexible titanium foil bag.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Structure of the flexible titanium foil bag.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Structure of the flexible titanium foil bag.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Given that the flexible titanium foil may deform during the welding process, the fabrication method of the titanium foil bag should be carefully designed to ensure the quality of the process. A special manufacturing process is presented here. Figure 11 shows a mandrel with the same cross section as the titanium foil bag was used to maintain the shape of the titanium foil during the welding process. After the foil body was welded, the mandrel was removed; the head, bottom, and foil body were then welded together. It should be noted that the longitudinal welding line is located on the short axis of the elliptic cross section of the foil body to avoid stress concentration (see section 4b for more details).
Manufacturing process of the flexible titanium foil bag.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Manufacturing process of the flexible titanium foil bag.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Manufacturing process of the flexible titanium foil bag.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
b. Stress and deformation analysis
FEA was conducted to verify the flexibility and deformation mode of the flexible titanium foil bag. Similar to the FEA of the titanium diaphragm described in section 3b, material nonlinearity, geometric nonlinearity, and contact nonlinearity were also considered during the FEA of the titanium foil bag. In the FEA model, an external load was applied to the titanium foil bag in steps. As shown in Fig. 12, when the external load reached 0.02 MPa, the upper and lower surfaces of the titanium foil bag began to touch. When the external load reached 0.10 MPa, most of the upper and lower surfaces of the titanium foil bag touched, and the volume of the titanium foil bag reached its minimum value. The simulation results of the contact status demonstrate that the titanium foil bag has sufficient flexibility, and only a small pressure differential is needed to change its shape.
Contact status of the titanium foil bag when the external load is (a) 0.02 and (b) 0.10 MPa.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Contact status of the titanium foil bag when the external load is (a) 0.02 and (b) 0.10 MPa.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Contact status of the titanium foil bag when the external load is (a) 0.02 and (b) 0.10 MPa.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
During the simulation process, the von Mises equivalent stress distribution of the titanium foil bag under different external loads was also acquired. As Fig. 13 shows, during the process of increasing the external load of the titanium foil bag, although the position of the maximum equivalent stress on the titanium foil bag shifted many times, it was mainly concentrated near the long axis of its elliptical cross section. As a result, stress concentration was avoided at the welding zones (the areas along the welding lines). Since the material of the welding zones is relatively brittle, the controlled deformation of the titanium foil bag increases the bags repeated usability.
Von Mises equivalent stress distribution of the titanium foil bag when the external load is (a) 0.04, (b) 0.06, (c) 0.08, and (d) 0.10 MPa.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Von Mises equivalent stress distribution of the titanium foil bag when the external load is (a) 0.04, (b) 0.06, (c) 0.08, and (d) 0.10 MPa.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Von Mises equivalent stress distribution of the titanium foil bag when the external load is (a) 0.04, (b) 0.06, (c) 0.08, and (d) 0.10 MPa.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
c. Endurance test
A laboratory experiment was conducted to assess the endurance life of the titanium foil bag. As Fig. 14 shows, a specialized test apparatus that can imitate the sampling process was designed. The test apparatus consists of a water cylinder with a flexible titanium foil bag inside, two piston cylinders, two linear actuators, and two timing relays. Piston cylinder 1 is directly connected to the left end of the water cylinder, and piston cylinder 2 is connected to the head of the titanium foil bag by a fitting screwed into the right end of the water cylinder. Before the test, the water cylinder is filled with water, the titanium foil bag is filled with air, and the water volume in piston cylinder 1 is more than 140 mL. When timing relay A is on, the two pistons move to the left simultaneously, driven by linear actuators 1 and 2. Then the water in piston cylinder 1 is squeezed into the water cylinder to compress the flexible titanium foil bag; the air in the titanium foil bag enters piston cylinder 2. Conversely, when timing relay B is on, the two pistons move to the right simultaneously, then the titanium foil bag fills with air again and returns to its original state. During this process, the air bubble will go into the water cylinder if the titanium foil bag ruptures, which can be observed as the water cylinder is transparent.
Setup to test the endurance of the flexible titanium foil bag.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Setup to test the endurance of the flexible titanium foil bag.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Setup to test the endurance of the flexible titanium foil bag.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Test results based on three titanium foil bags are shown in Table 1. According to the experiment results, the three titanium foil bags had a similar endurance, which may be caused by defects in the manufacturing process of the titanium foil bags, such as the slight twist of the titanium foil bag around the axis and the size deviation. Given that the average service life of the three titanium foil bags is about 17 uses, we can consider changing a new titanium foil bag after the sampler has been used more than 15 times. This is acceptable since the cost of a titanium foil bag is quite low.
Results of the endurance test.
d. Organic carbon blank test
A comparison experiment was also carried out to examine the organic carbon blanks of the titanium foil bag and traditional sample cylinder with O-ring seals (fluoroelastomer). During this experiment, one titanium cylinder and two identical titanium foil bags (noted as bag 1 and bag 2) were employed. Thorough cleaning of the sample containers has been conducted as the following procedure before experiment. The titanium sample cylinder and bag 1 were washed with successive rinses of volatile organic solvent (e.g., methanol) according to the reference (McCollom et al. 2015), and then rinsed three times with Milli-Q water. Bag 2 was combusted at 450°C for 6 h to remove any trace of organic matter and then rinsed three times with Milli-Q water. After the rigorous cleaning procedure, all sample containers were filled with about 140 mL Milli-Q water and kept in the laboratory for 24 h. Then the water samples were transferred directly to precombusted (6 h at 450°C) glass bottles and refrigerated at 4°C until analysis. The dissolved organic carbon (DOC) of each water sample as well as Milli-Q water was repeated analyzed by Shimadzu TOC-L Analyzer.
As shown in Fig. 15, the instrument organic carbon blank ranged from 10 to 16 μM C with an average value of 13 ± 2 μM C. After subtracting Milli-Q water blank, the average organic carbon blanks of the cylinder, bag 1 and bag 2 were 27, 9, and 3 μM C, respectively. From the results we can see that the titanium foil bag had an obviously lower organic carbon contamination compared to the titanium cylinder at the same cleaning condition. Moreover, the titanium foil bag was able to be combusted at high temperature (450°C), which could further reduce the organic carbon contamination. So it allows an optimized cleaning procedure and experimental protocol for DOC studies as suggested by previous literature (Yoro et al. 1999; Spyres et al. 2000).
Results of the organic carbon blank test.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Results of the organic carbon blank test.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Results of the organic carbon blank test.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
5. Preliminary field test
The sampler was constructed and tested in the field at the Longqi hydrothermal field in the southwest Indian Ocean during Cruise TS 10 from 10 November 2018 to 10 March 2019. During the sea trial, the sampler was deployed four times by the manned submersible Shen Hai Yong Shi. During the first two dives, the sampler was fixed on the submersible’s basket, and two samples of bottom seawater were collected near the hydrothermal vent. During the last two dives, the sampler was operated by the manipulator on the submersible to collect hydrothermal fluids (Fig. 16). After the sampler was recovered from the seafloor, the pressure and volume of the sample were measured immediately. A summary of the samples is given in Table 2. The general results of the field deployment demonstrate that the sampler works well at the seafloor and is capable of collecting pressure-tight hydrothermal fluid samples.
Collection of hydrothermal fluid using the pressure-tight sampler.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Collection of hydrothermal fluid using the pressure-tight sampler.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Collection of hydrothermal fluid using the pressure-tight sampler.
Citation: Journal of Atmospheric and Oceanic Technology 37, 11; 10.1175/JTECH-D-20-0017.1
Record of the sampler in the sea trial.
6. Conclusions
A pressure-tight hydrothermal fluid sampler with a metal seal was successfully designed and constructed. Since all its components that come into contact with the sample are made of titanium or titanium alloy, this sampler is well suited to collect high-temperature hydrothermal fluid for the measurement of organic matter. Meanwhile, owing to its pressure-maintaining capability, the sample collected by this sampler can also be used for the quantitative analysis of gas components and the investigation of barophilic microorganisms.
Acknowledgments
We are grateful to the crews of R/V Tan Suo Yi Hao and HOV Shen Hai Yong Shi for their support during the sea trial. This work was supported by the National Natural Science Foundation of China (Grant 51879232) and the National Key Research and Development Program of China (Grant 2016YFC0300500).
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