[M-IS22] Interactions of Geosphere-Hydrosphere-Biosphere and Deep-sea Methane Environments

[MIS22-P01] Distribution of methane seep in the Sea of Okhotsk off Abashiri and consideration of sampling method

*Nakamura Kotomi¹, Satoshi Yamashita¹ (1.Kitami Institute Technology)

Keywords:methane hydrate, methane seep, mesh structure

Shallow methane hydrates have been collected on multiple research cruises in the Sea of Okhotsk off Abashiri. In places where shallow methane hydrates are present, gas bubbles (methane seep) erupting from the seafloor are often observed using a quantitative echo sounder or a multibeem echo sounder. Methane is also a greenhouse gas with 20 times the greenhouse effect of carbon dioxide, and understanding the distribution and amount of methane seep discharge will lead to a better understanding of global environmental changes. In addition, depending on the seeping scale, it also has potential as a resource. Many methane seeps have been confirmed off the coast of Abashiri, but the exact number of methane seeps is not known because the same location has been surveyed on multiple cruises. Therefore, in this study, we observed methane sheep in a wide area of the Sea of Okhotsk off Abashiri using a multi-beam echo sounder and determined the exact number of seeps. In addition, we investigated the sampling method of seeping methane gas.
In the study of the sampling method, we considered using a recovery membrane (net) as a method of gas sampling. Advantages of using a mesh structure include the following. 1) A recovery device can be manufactured at low cost. 2) Due to the mesh structure, there is little resistance due to tidal currents, making it easy to install on the seabed. 3) Excess gas can permeate the mesh and leak to the outside. In order to devise such a recovery device, we created a model of the recovery device, conducted simulation experiments in the actual ocean, and investigated the possibility of gas recovery.