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  • Geological sampling

    •  Mud, sand, and other substances that flow into the ocean from the land via rivers and the atmosphere accumulate on the seafloor and form sedimentary layers. The materials generated in the ocean by biological production processes or chemical reactions are also deposited at the same time, and the global environment at that time is recorded in the sediments of the seafloor from moment to moment. Therefore, it is believed that the analysis of seafloor sediments can be used to elucidate the evolution of the global environment from the past to the present and to predict climate change in the future.　

       On the other hand, there are places on the seafloor where the crust is exposed, such as ocean ridges. The distribution characteristics of the rocks that make up the crust can be traced to faults and plate motions, and analysis of crust and rocks collected from the seafloor is expected to elucidate the mechanisms of earthquake generation.

       Since geological samples collected vary in particle size, hardness, and viscosity depending on the purpose of the research and the area of the sea, various instruments have been developed to efficiently collect geological samples. In addition, acoustic instruments such as multinarrow-beam bathymetry (seafloor topography survey equipment) and sub-bottom profilers are sometimes used to investigate the shape and characteristics of the seafloor prior to observation and to ensure safe and accurate sample collection. In recent years, it has become clear that useful resources such as natural gas and methane hydrate exist on the seafloor, and geological samples are also collected for the purpose of seafloor resource surveys.


    • 地質試料採取　採泥器　ドレッジ

      　　　　　　　　　　　 　Fig.1  Schematic of geological sample collection observation

      ピストンコアラー Piston corer

      マルチプルコアラー Multiple corer

      ボックスコアラー Box corer

      オケアングラブ採泥器 Okean grab sampler

      スミス・マッキンタイヤ採泥器 Smith Maclintyre grab sampler

      ドレッジ Dredge

      ロックコアラー Rock corer

      Because most of the equipment used to collect geological samples shown in Figure 1 is large and heavy, observation work is performed using a gantry crane (A-frame) equipped at the rear of the observation vessel.

      This section introduces columnar samplers, grab samplers, other samplers, and crust and rock samplers that are currently used for geological sampling.


  • Columnar sampler

    • A columnar sampler is a generic term for an instrument that collects sediment samples by piercing a cylindrical cylinder into the seafloor. Since this type of instrument can collect samples without disturbing the stratigraphy of the sedimentary layers, the collected samples are analyzed and classified according to their ages. Typical columnar samplers include piston corers, multiple corers, G.S.type core sampler（ASYURA）, Freger core sampler, and HR type core sampler.

    • ・Piston Corer

       The piston corer is a gravity free-fall type sediment sampler. A metal cylinder connected under the main weight is thrust into the seafloor to collect sediments in a cylindrical shape from several meters to a maximum of 20 meters below the seafloor. It is the deepest mud sampler of its type, and the collected samples can be used to estimate the earth's environment hundreds to hundreds of thousands of years ago.

       The observation workflow for the piston corer is as follows. First, the main body of the piston corer is connected to the trigger of the balance type and lowered to the seafloor using a winch. When the pilot weight contacts the seafloor, the trigger operates and the corer drops freely, penetrating the seafloor by its own weight and momentum. The characteristic of the piston corer is that negative pressure is generated by the piston rising inside the cylinder during penetration, allowing the sampler to penetrate smoothly and deeply. This negative pressure also prevents the loss of samples from the bottom of the pipe (Figure 2).

      　On the other hand, since the sediment surface samples are disturbed when the sampler is thrust into the seafloor, a small corer is used for pilot weights and the sediment surface is sampled separately.

      ピストンコアラー

      　　　　　　　　　　　　　　　　　Fig 2 Piston Corer and Piston Corer Schematic

      天秤式トリガ　trigger arm

      メインウェイト　main weight

      採泥管　corer tube

      メインワイヤ　main wire

      ピストン　piston

      パイロットワイヤ　Trigger wire

      パイロットウェイト　Trigger weight, release weight

      　

      Link to detailed course→「ピストンコアラー」

    • ・Multiple corer
       As shown in Figure 3, the multiple corer consists of a wreck constructed of metal pipes, a weight that moves up and down inside the wreck, and a polycarbonate cylinder attached to the weight. When the mast reaches the seafloor, the weight descends and the tube quietly penetrates into the sediment, collecting sediment up to about 30 cm above the seafloor surface, together with water directly above the seafloor. It is called a multiple corer because multiple tubes can be attached.

      　Samples collected with this sampler are brought on board directly from the seafloor environment because the sediments are not agitated in the cylinder. Therefore, it is widely used to study the interaction between the water directly above the seafloor and sediments through mass exchange, and the dynamics of microorganisms that specifically inhabit the surface layer of sediments.


      マルチプルコアラー

      　　　　　　　　　　　　　　Fig 3 Multiple corer

      　Link to detailed course→「マルチプルコアラー」


    • ・G.S.type core sampler（ASYURA）

      　This is a small columnar sampler with three polycarbonate tubes attached to a weight. Although it does not have a harp like a multiple corer, it can collect the same samples as a multiple corer if it is allowed to penetrate slowly into the seafloor. The top and bottom lids close when pulling out from the seafloor to prevent sediment samples from falling, the same mechanism as the multiple corer.　
      　By attaching this sampler as a pilot weight for piston corer observations, the sediment surface layer, which is disturbed by the piston corer, can be sampled simultaneously in a series of observation operations.


      　　　    

      　

       　　　　　

      　　　　　　　Fig 4　G.S.type core sampler（ASYURA）

      ※ Picture provided by : Hokkaido Research Organization（HRO）


    • ・Freger core sampler

      　The Freger core sampler is a gravity free-fall columnar sampler shaped like a rocket with a weight on top of a metal cylinder. The weight and the force of the free-fall through the sea allow it to penetrate the seafloor and collect sediments in a few dozen centimeters of the seafloor surface layer. A polyvinyl chloride or acrylic tube (inner tube) is inserted into the cylinder, and the collected sediment is held inside the tube. The lower part of the tube is equipped with a metal check valve, and the upper part of the tube is equipped with a lid that closes when the mud sampler is lifted out of the water, preventing the collected sediment from falling out.

      　Since this sampler is relatively small and can be carried by human power, observation work can be done by hand without the need for winches, cranes, or other equipment. Therefore, they are mainly suited for surveys in inner bays and coastal areas such as Tokyo Bay and the Seto Inland Sea. It can also be used as a pilot corer for a piston corer as well as an ashlar corer.


      　　Fig 5 Freger core sampler

      　 Picture provided by：RIGO Ltd.

      　


    • ・HR type core sampler

      　The HR type core sampler is a sampler with a metal bit attached to the end of an acrylic tube connected to a weight. Upon arrival at the seafloor, a trigger on the top of the weight activates the bit, which slowly penetrates the seafloor under its own weight. When the wire or rope is pulled up, the bit rotates 90 degrees to form a lid that prevents the sample from falling out. Because of this mechanism, the device is most commonly used in inner bays and lakes where sediments are soft. The weight of the main body of the device is only enough to be lifted by human power, making it suitable for surveys conducted by small vessels.


      　　Fig 6 HR type core sampler

      　Picture provided by：RIGO Ltd.

  • Grab sampler

    • 　Grab sampler is a generic name for a type of sampler that uses a semicircular bucket (grab bucket), which opens from side to side, to grab and collect sediments on the seafloor like a crane game. Although the sample is disturbed during collection, it is a simple method to investigate the nature of the sediment surface layer and the composition of components in the sediment. It is also used to collect benthic organisms living in the sediment and on the seafloor surface. Typical grab-type mud samplers include the Okean grab sampler, Smith McIntyre sampler, and Ekman barge sampler.

    • ・Okean grab sampler

      　The Okean grab sampler is a grab-type mud sampler that combines a grab bucket and a balance trigger. When the grabbing device approaches the seabed, the balance trigger operates, causing the grabbing device to free-fall. The momentum of the fall causes the grab bucket to dip into the seabed. The weight of the grab bucket is so great that it can collect samples even from relatively hard bottom sediments such as sand and gravel. When the wire is wound up, the grab bucket grabs the sediment and closes the top cover of the grab bucket in conjunction with it. The top cover keeps the sample in the bucket from being lost in the sea when the grab bucket is retrieved. If the bottom sediment is too soft, the grab bucket will be buried in the seabed and the mud sampler will not be able to collect samples from the sediment surface.


             Fig 7 Okean grab sampler

      ※Picture provided by：Geological Information Research Division, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST)

      オケアングラブ採泥器
      　　　　 　Fig 8 Okean grab sampler and its working schematic

    • ・Smith McIntyre Grab sampler

      　The Smith McIntyre Grab sampler is a grab-type sampler that combines a grab bucket and a device that closes the bucket using the force of a spring in a metal frame. The main body of the grab bucket is dropped freely from near the seafloor, and the mud sampler is allowed to sink to the seafloor. Usually, the grab bucket is buried to the part of the grab bucket, and at the same time, a trigger attached to the frame operates to close the grab bucket and its top cover. This mud collector is lighter than the Okean grab sampler because the thickness of the grab bucket is thinner. If the bottom sediment is relatively hard, additional weights can be attached to the frame to increase its own weight for observation. It is often used for biological surveys in shallow water areas because it is easy to handle and can gouge out a fixed area of the seafloor.


      　 Fig 9　Smith McIntyre Grab sampler

       Picture provided by：Tottori Prefectural Fisheries Experiment Station.　（https://www.pref.tottori.lg.jp/item/838972.htm）

      スミスマッキンタイヤ採泥器
      　　 Fig 10 Smith Macintosh tire sampler and schematic diagram of its operation.

    • ・Ekman barge sampler

      　This is a grab-type mud sampler with a grab bucket attached to the bottom of a cubic box that is closed using the restorative force of a spring. First, the grabbler is lowered to the seafloor and allowed to land on the bottom. Then, when the messenger is dropped and the trigger is activated, the grab bucket closes and the sediment is collected. This is the simplest and smallest of the grab type mud samplers and is suitable for simple surveys in lakes, bays, and coastal areas.


      　　　図１１　Ekman barge sampler

      　　※Picture provided by：RIGO Ltd.

  • Other samplers

    • ・cylindrical dredge

      　A cylindrical dredge is simply a metal cylinder and is a very simple sampler. The dredge collects sediments by scooping them up on the seafloor. Once the dredge is lowered to the seafloor, it is towed to the surface to scoop out the surface sediment. Since this is a simple dredge, the sediment layer will be agitated during collection, and some of the sample will be washed off during retrieval to the vessel. Benthic organisms can be collected even in rough sandy soil.

      円筒ドレッジ

      　　　　　　　　　　　　　Fig 12　Cylindrical dredge

      　

  • Crust and rock sampler

    •  Crustal and rock samples are collected by crushing or scraping crust and rocks using a sampler. Since most of the seafloor is covered by sediments, it is necessary to precisely locate exposed seafloor areas such as ridges in order to collect rock samples. In addition, such terrain is often so rugged that the sampler often gets caught, requiring different observation and maneuvering techniques from those used when handling mud samplers. Here we introduce some rock-related sample collectors.

    • ・Chain-bag dredge

      　A chain-bag dredge is a collector that combines a net made of metal chains and a mud box, which is towed over a rocky seafloor or ridge to scrape off and collect samples. It is similar in shape to a biodredge, which collects organisms living in the sediment, but uses a net made of chain so that it will not be destroyed by rubbing on the hard seafloor. The collector is towed by moving the vessel forward once it reaches the bottom of the sea floor. Another method is to collect sediment and rock samples simultaneously by using a combination of a chain-back dredge and a cylindrical dredge as shown in Figure 1, where the seafloor is mixed with sediment and rocks. Since the dredge drags over an uneven seafloor, the collecting instrument may get caught on the seafloor. Therefore, the tension on the wire is constantly monitored during the observation, and when an abnormal tension is observed, the collector is retrieved by using the ship's maneuvering technique so that the collector is released from the seafloor.

      　Fig 13　chain-bag dredge

      ※Picture provided by：Geological Information Research Division, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST)

    • ・Rock corer

      　The rock corer is a metal pipe with a weight at the top and a metal fixture for crushing and collecting rock at the bottom end. The collector is impacted onto the seafloor, where the crust and rocks are exposed, and the crushed sample is collected by sticking to the grease applied to the tip of the instrument and the side of the weight. It was developed to collect even a small amount of rock samples from the seafloor, where towing a dredge is dangerous due to the jagged and complex topography, such as ocean ridges.

      ロックコアラ―

      　　　 　Fig 14　Rock corer

      　

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