Research methods

Oceanographic observations were conducted in Funka-Bay, Hokkaido (2018-2019) and in the northern Bering Sea and southern Chukchi Sea (July 2017 and July 2018) (Figure 1). The training ship Ushio-Maru (Picture 2 left) and the training ship Oshoro-Maru (Picture 2 right) were used for the research cruises.

Figure 1　Observation sites　a: Map of the North Pacific Ocean including observation sites, b: Location of Funka-Bay, Hokkaido、c: Observation station in Funka-Bay (St30), d: Observation stations in the northern Bering Sea and southern Chukchi Sea

Picture 2 (Left) Training Ship Ushio-Maru, (Right) Training Ship Oshoro-Maru

［Sediment sampling］

We used an Ashura-sampler for the Ushio-Maru and a multiple core sampler for the Oshoro-Maru. We collected water directly above the sediment and pore water in the sediment section with a Mizutol by cutting the sediment into 1 cm thick sections.

Picture 3　Sediment samples from Funka-Bay (April, just after the diatom bloom) and the Ashura sampler (right), Diatom aggregates are deposited on the sediment surface.

Picture 4 (Left) Multiple core sampler observations in the northern Bering Sea, (Right) Sediment Sample

［Seawater sampling］

Seawater was sampled vertically with CTD water sampling equipment (Picture 5).