Deep water dive with Shinkai6500
Team members assisting the submersible Shinkai6500, A.Prof. O. Alard and Dr Y. Gréau holding a recovered piece of mantle rock and the expedition Research Vessel Yokosuka. Image: O. Alard, Y. Gréau & YK24-10S crew.
NCRIS enabled AuScope Geochemistry Network researchers recently joined an international team to recover unique underwater volcanic rocks found along deep oceanic subduction trenches. The team dived 6,500m below sea level in the manned deep submergence vehicle (DSV) Shinkai6500 (しんかい 6500).
Overview
Associate Professor Olivier Alard and Dr Yoann Gréau from the NCRIS enabled AuScope Geochemistry Network participated in an expedition co-led by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and the Atmosphere and Ocean Research Institute (AORI) of The University of Tokyo.
The team sampled lava and its cargo of mantle xenoliths from the “Petit Spot” volcanoes. These volcanoes form as a result of tectonic plate flexion. In this case, the volcanoes the team visited form as the Pacific Oceanic Plate flexes to dive below the islands of Japan.
The etymology of mantle xenoliths hints at their origin. Xeno from Greek xenos "a guest, stranger, foreigner and lith "stone". These rocks form as volcanic lava traps older mantle rock as it travels to the surface – providing researchers with a useful way to sample the deepest parts of the Earth.
The scientific team and the Shinkai crew of the deep sampling campaign (YK24-10S) posing in front of the Shinkai6500 DSV. The lead scientist (Dr Norikatsu Akizawa, Tokyo University) and the Captain of the research vessel hold in their hands the exceptional samples that were retrieved (See below). Image: YK24-10S crew
Activity
The team left Tokyo Bay and sailed 750 km from the east coast of Japan. They spent eleven days aboard the RV Yokosuka before landing in Sendai. Over four days, they completed four dives with the Shinkai6500, each taking between 8 and 9 hours, with 3 hours of work on the seafloor.
The team collected several rare mantle xenoliths (shards of peridotite), carried to the surface by ascending lava, along with samples of volcanic rocks known as peperites.
The powerful mechanical arm of the Shinkai collects a large block of basalt containing bountiful mantle xenoliths. Image: Yoann Gréau
Analysis of the xenoliths will provide insights into the evolution and dynamics of the Earth’s mantle, the role of deep underwater volcanism in the biogeochemical cycle, and its potential influence on the development of early life on Earth.
A selection of mantle peridotite xenoliths collected during the expedition. Image: YK24-10S crew
The team will also investigate the recovered peperite samples. These rocks form from the interaction of magma and water-rich sediments on the ocean floor. Analysing these samples will potentially provide insights into the mechanics of tsunami-generating earthquakes.
Peperites found 6434m below the ocean’s surface. Image: YK24-10S crew
“The sampling exceeded our expectation with countless large mantle fragments seemingly sampling the deepest part of the oceanic lithosphere, which is truly a first in this geological context.
This will shed some new light on the aging of oceanic plates, but will also give a better constrain on what enters the subduction factory plunging below Japan”
– Dr Norikatsu Akizawa
End of a long day for Yoann Gréau, Yohey Suzuki and pilot A. Ishikawa, arriving back from their dive after a successful sampling operation at 6,442 m. Image: Norikatsu Akizawa
Future Impact
The samples will be analysed in the new AuScope enabled geochemical facilities at the Australian National University, using state-of-the-art mass-spectrometers and radiometric dating. This will be a rare opportunity to generate insights into mantle dynamics, biogeochemical impacts of underwater volcanism and the mechanics of tsunami-generating earthquakes. These findings could have implications for predicting natural disasters and understanding the conditions that might support life on other planets. Stay tuned!
STORY IN A NUTSHELL
In June 2024, NCRIS-enabled researchers joined a JAMSTEC mission off Japan's coast to explore deep-sea volcanoes to enhance our understanding of Earth's mantle dynamics, biogeochemical cycles, and tsunami mechanics.
AUTHORS
Dr Yoann Gréau & Philomena Manifold
FURTHER READING
Shinkai 6500
