Pump Sampling

　By using a pump, surface seawater can be collected continuously.

The seawater supplied to onboard laboratories and other places necessary for research is called "research seawater." It is distinguished from "miscellaneous seawater" used for cooling ship engines, washing hulls, and sanitary purposes by the seawater intake, pumps, and piping on the ship's bottom. In addition, several considerations are made in the pumps and piping used for intake of seawater for research purposes in order to suppress changes in liquid quality. While the quality of seawater for miscellaneous use is changed by adding drugs or killing microorganisms through electrolysis at the time of seawater intake to prevent organisms from adhering to the piping, seawater for research use is taken without changing the composition of the seawater as much as possible. For this reason, pipes with resin-coated inner walls are used to prevent corrosion inside the pipes, and pipes are cleaned periodically to remove contaminants deposited inside. The "research seawater" thus pumped can be collected at any time during the voyage, regardless of the ship's navigation or weather conditions, so that information on the sea surface (water temperature, salinity, etc.) along the route can be continuously measured and recorded by feeding the surface seawater monitoring system (Figure 3, 4).

Figure 3  Measurement section of the surface monitoring system of the Oshoro Maru (Hokkaido University)

クロロフィル・濁度センサ： Chlorophill and turbidity sensor　　水温・塩分センサ： Temperature and salinity sensor　　流入口：inlet　　研究用海水：Research water

The surface monitoring system consists of a combination of a measurement unit, which is a container filled with surface seawater and equipped with various sensors, and a control unit that records the acquired data or distributes the data to various key locations. The measurement unit is located near the sink in the laboratory and is constantly supplied with seawater for research purposes. The tank is filled with seawater, and two underwater sensors inserted into the tank measure water temperature, salinity, chlorophyll, and turbidity, respectively. The tank is designed so that research seawater is supplied from the bottom of the tank and overflows from the top, preventing the generation of air bubbles that could cause abnormal sensor readings. In addition, the tank is made of light-shielding and non-reflective material so as not to affect the optical sensors (chlorophyll and turbidity). The information acquired by the measurement unit is stored in a PC for data recording via a cable connected to the sensor, and is displayed sequentially by dedicated software.

Figure 4  SST observed by the surface monitoring system (SST: Sea Surface Temperature)

On the other hand, seawater collected by the ship-bottom pumping method contains metallic elements eluted from the hull and piping, and thus cannot be used as a test water for the analysis of trace metals in seawater. Therefore, a towing body method is used to continuously collect seawater over a wide area with little contamination from the vessel's hull.

A boom is used to lower the towing structure away from the hull of the vessel, and the vessel is then allowed to navigate, pumping seawater overboard from the end of the towing structure. In this way, seawater samples can be collected without contact with the hull (Figure 5).

Figure 5  Conceptual diagram of water sampling of a towing body