Section outline

    • Collecting seawater from an arbitrary depth in the ocean is called "vertical water sampling," and the equipment used for this purpose is called a water sampler. The water sampler is attached to a wire rope with the lid open, lowered to the desired depth, and then the lid is closed to collect seawater at that spot. A weight called a messenger is dropped from the vessel along the wire rope, which activates the trigger of the water sampler to close the lid (Figure 6).

    • 採水器の仕組み

      Figure 6   Water sampling by messenger

      上蓋： upper lid        下蓋： bottom lid        ゴムチューブ：rubber tube        採水筒：bottole        トリガー：trigger        ワイヤロープ：wire rope        メッセンジャー：messenger


        

    • By having multiple water samplers attached to a wire rope at arbitrary intervals, seawater can be sampled from several different depths in a single operation. As soon as the messenger activates the trigger, the next messenger starts falling toward the lower level, so that the lids are closed one after another from the upper-level sampler to the lower-level sampler (Figure 7).

    • ニスキン採水器　連装方式による採水

      Figure 7  Multi-layer water sampling using a series of water samplers

      水深：depth        メッセンジャー：messenger        リリースピン解除：release pin disengaged
      a) Attach multiple water samplers to the wire rope at desired intervals and lower them into the water.　b) Each water sampler is left with its lid open and a messenger hanging from the trigger.　c) When the messenger arrives from the upper layer, the lid of the water sampler closes, and at the same time, the messenger begins to fall toward the lower layer.

    • Several types of water samplers have been invented over time, but the basic structure remains the same in that it consists of a "sampling bottle" that stores seawater and a "lid" that closes the sampling bottle.


      The well-known water sampler that has been widely used since the early 20th century is the Nansen bottle, which is made of metal (brass). This device has a mechanism that closes the upper and lower valves when the water sampler is tipped over, and when used in combination with a tipping thermometer*, it was widely used for oceanographic observation because it could simultaneously measure the depth of water sampling and the temperature of the water at the site. Toward the end of the 20th century, as analytical items became more diverse and analytical accuracy improved, improvements were required in water sampling methods. The Nansen sampler, which was made of metal (brass), heavy, and limited in its capacity to collect seawater, was replaced by a newer type of sampler. Currently, the most widely used type is the Niskin bottle, which has both a water sampling bottle and lid made of polyvinyl chloride and is available in a wide range of sizes from 1.2 to 30 liters (Figure 8).

    • Figure 8  Niskin water sampler

    • ※ Tipping thermometer

      　A special glass-mercury thermometer that, when tipped over, cuts the mercury bulb part and the mercury column at the cutting point, and the length of the mercury column at the time of tipping over, is preserved. By comparing the indicated values of the "pressure-proof type," which is not subject to water pressure, and the indicated values of the "pressurized type," which is subject to water pressure, the water depth (or more precisely, water pressure) at the time of tipping over can be determined (Figure 9).

      転倒温度計

      Figure 9  Tipping thermometer

      主温度計：main thermometer　　副温度計：sub thermometer　　防圧型：pressure-proof type　　被圧型：Pressurized type　　転倒：tipping　　死管：dead pipe　　切断点：cut-off point　　環状部：ring section


    • In the 1980s, the CTD water sampling system (Figure 10) was developed, allowing water sampling simply by sending an electrical signal from the vessel without using a messenger. This system collects seawater by closing the lid of the sampler at any depth while acquiring real-time information on water temperature and salinity at each depth, thus enabling more accurate and reliable water sampling at any depth compared to the conventional wire-coupled system. The CTD water sampling system is used as the standard water sampling method on major research vessels.

    • Figure 10  CTD water sampling system