Where exactly are we going?

Our field site is a small-ish volcanic system in the sediment filled back-arc (rifting) basin behind the southern portion of the greater Japanese island arc system. It’s about 200km NW of Okinawa Japan. The sediments are a mixture of terriginous sediments (mainly from the Yangtze river) and local volcaniclastic sediments (mostly pumice).  Our hope is to drill in three sites: at the summit of the hydrothermal mound, at the foot of the mound, and out on the flank of the volcanic system. We are taking piston-cores in the softer sediments.  Once we reach ~50m below the seafloor we will likely have to switch to an industrial drill core because the sediments will be too consolidated for the piston-corer. The planned sites will give us insight into the lateral (horizontal) flow of hydrothermal fluids through the mounds. Previous work in the area suggests that the fluid flowing laterally has a different chemical composition from the fluid flowing through the main hydrothermal vent due to a process called phase separation. This occurs when the water boils beneath the surface and partitions into a vapor and a liquid phase. We hypothesize that the differences in the chemical composition of the fluids will lead to differences in the microbial communities present in the main vent  sediments and the sediments on the flanks of the mound.

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