3) Mud sampling procedures

To obtain samples efficiently, it is necessary to have a good understanding of how to prepare the mud sampling equipment and how to process the collected samples. Care must be taken when working on board as there is a risk of the mud collector shaking due to ship motion and wind. This section describes mud sampling operations using a Smith-McIntyre mud collector, following the workflow in the order of (1) setting up the collector, (2) inputting operations, (3) landing on the bottom, (4) lifting operations, (5) sample handling and (6) recording observations, respectively.

3)-1 Setting up the mud collector

Set-up of the mud collector is carried out before the sampler is placed in the water. Set-up means fixing the bucket in the open position (set on the trigger) and connecting it to the observation winch wire. The photographs in Fig. 6 show the conditions before and after set-up respectively.

Fig. 6 Before (left) and after (right) setting of the mud collector

3)-2 Inputting operations

Once the set-up is completed, the observation winch is operated and the mud collector is put into the sea. Touching moving parts such as the landing plate or landing plate arm during the operation may cause the trigger to malfunction. Therefore, work should be carried out without touching any part other than the support frame and without allowing it to come into contact with the vessel’s hull.

3)-3 Landing on the bottom

Once the mud collector has been placed in the sea, the winch is unloaded and the mud collector is lowered towards the seabed. An example of winch operation (winch operation) when lowering the mud collector to the bottom is shown in Fig. 6. First, the wire is unrolled at a speed of 1 m/sec while checking the depth of the water and the length of the unrolled wire (Fig. 6-①). When the length of the wire reaches a depth of -10 m, stop unrolling and wait until the wire is pointing straight down (Fig. 6-②). If the wire is unrolled while it is tilted, the mud collector may land on the bottom at an angle and the trigger may not operate. After waiting, resume unloading at the maximum speed of the winch to allow the mud collector to fall freely (Fig. 6-③). As soon as the mud collector has reached the bottom, immediately stop the wire ejection (Fig. 6-④). The mud collector is considered to have reached the bottom when the tension on the wire decreases. As soon as the mud collector has reached the bottom, the trigger of the mud collector finishes operating and the wire starts winding at low speed (0.3 m/s) without a pause (Fig. 6-⑤). As the wire is wound up, the tension gradually increases, and when a constant tension is observed, the mud collector can be confirmed to have left the bottom. The hoisting speed is then increased and the mud collector is quickly recovered on board (Fig. 6-⑥).

Fig. 6 Winch operation on landing

3)-4 Lifting operations

Take care not to allow the mud collector to come into contact with the hull or touch the bucket arm when lifting it from the sea to prevent the bucket from opening and spilling the sample. The lifted mud sampler is then returned to its original position on a dedicated platform. The top lid of the closed grab bucket can be opened to reveal the sample collected (Fig. 7).

Fig. 7 Collected sediments and immediate seawater

3)-5 Sample handling

The collected samples are processed according to the purpose of the research.

If the organisms in the sediment are to be surveyed, the sample (Fig. 8) is removed from the bucket onto a tray or similar and processed through a sieve to select the biological samples from the sediment. The sediment is then poured over with seawater to wash away the sand and mud, and the organisms remaining on the sieve (Fig. 9) are picked up. The size of the sieve is selected according to the size of the biological sample to be collected or the rock particles contained in the collected sediment. In other words, select a sieve with a mesh size that is smaller than the desired sample, so that only the unwanted mud or sand flows out.

Fig. 8 Sediment samples collected in trays

Fig. 9 Biological samples remaining on the sieve

二枚貝: bivalves 甲殻類: crustaceans 巻貝: conchs 多毛類: polychaetes

Sediments are formed by the accumulation over time of mineral particles of terrestrial origin and materials resulting from bioproduction processes, which can be analyzed at different depths to estimate the environment at different ages. When sediment samples are used for this purpose, they are treated differently to those used for benthic studies. First, the top lid of the bucket is opened and seawater is removed using a silicon tube or syringe to prevent sediment surface run-off. This seawater can be analyzed as a direct seawater sample. The sediment surface layer has a high water content and is very soft, so it is scooped out with a spoon or similar. A pipe is then inserted to cut through the sediment into columns, which are then pushed out of the pipe to distribute the sample into layers of arbitrary thickness and to age the sample.

3)-6 Recording of observations

Information on how the samples were collected is the most fundamental data for surveys and research. Therefore, the “date and time” and “location” (expressed as latitude, longitude, and depth) of the mud sampling, as well as the “properties of the obtained samples” should be recorded. In addition, different symbols and numbers should be determined for each mud sampling operation, and these should be written in both the field notebook and on the sample’s label, so that it is easy to look back to see how each sample was obtained.

By recording not only the sample itself but also supplementary information such as the sea conditions at the time of the work and the specifications of the mud collector used, it can be used as material when considering the next sampling point and sampling method. Many research institutes prepare special sheets (field notebooks) to systematically keep records.