Course Content

View of collecting a sediment trap placed in the Chukchi Sea (Pacific Arctic Ocean land shelf area) (LASBOS youtube video)

　Sediment traps were installed in the land shelf area of the Chukchi Sea (north of the Bering Strait) in the Arctic in July 2017 by the research voyage of the training ship Oshoro Maru of the Faculty of Fisheries of Hokkaido University. The purpose of the trap is to capture (trap) particles that accumulate on the bottom of the Arctic Ocean for one year. In July 2018, one year after the trap was installed, the Oshoro Maru headed back to the Chukchi Sea to collect the sediment traps. The sediment traps are connected to a weight (about 500 kg) that is dropped to the seafloor. The weight is connected to the sediment trap by a disconnecting device. The first step is to send an ultrasonic command to the detachment device. The first nerve-wracking part is to see if we get a response. If there is no reply, the detachment device has either malfunctioned or has been swept away and lost. We then send the detachment signal and detach. The next nervousness is, "Will it really float? If the weight and the rope of the sediment trap are entangled, it will not float. If the float is damaged, it will not float. The surveyor, the crew, and the entire crew will be watching the situation.

Sediment trap observation to capture settling particles

　The only way to capture particles settling in the ocean is to submerge a large roto in seawater and collect particles falling from above. A cup is placed under the large rote to collect the particles and is rotated by a timer device. The particles that settle in each season can be collected in the cup. This is called a sedimentation trap. Every year, we have to go out to the distant ocean by observation ship to set up and collect the sedimentation traps. Currently, JAMSTEC is actively conducting sediment trap observations in Japan. Although it requires considerable effort and expense, it has provided valuable data for understanding the global environment, such as seasonal changes in sedimentation particles, factor analysis through component measurements, and long-term trends that can be captured by continuing the program for many years.

　Sediment traps moored in the ocean can become unrecoverable due to some malfunction. Not only is the observation data lost, but the loss of expensive equipment is also a major economic blow. When we throw in a trap, we pour sake over it to purify it before throwing it in. (I'm not kidding.) After the trap has been deployed, it is up to God to take care of it.

①　We transport the sediment traps by observation vessel to the area where we observe the settling particles

②　Sediment traps are moored in the ocean and sedimentation particles are collected in sample cups for one year. The 24 sample cups are strung together so that they can be collected twice a month for one year.

③　A year later, an observation ship will be in the same area, the sediment traps and weights will be detached, and the sediment traps will be floated.

④　On board, the sample cup is removed from the sedimentation trap and the settled particles are processed.

　In the past, the School of Fisheries Sciences at Hokkaido University also continued to conduct sediment trap observations, but no longer does so. We sometimes send out the Training Ship Oshoro-Maru to conduct sediment trap observations for large-scale research projects, such as the Arctic Research Project.

セジメントトラップ観測　Sediment Trap Observation

浮き玉　floating ball

切り離し装置　Detachment device

自動回転　Automatic rotation

観測船　Observation Vessel

季節変化　Seasonal change

冬　Winter

春　Spring

夏　Summer

秋　Autumn

成分測定　Compositional Measurements

炭酸カルシウム→円石藻　Calcium carbonate → circular calcareous algae

珪酸→珪藻類　Silicic acid → diatoms

鉱物→ダスト　Minerals → dust

有機物→生物生産　Organic matter → biological production

長期モニタリング　Long-term monitoring

トレンド解析　Trend analysis