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Chinese drillship retrieves rock from deep South China Sea

Mengxiang brought up basalt cores from water about 4,100 metres deep, but the geological conclusions remain preliminary.

The Chinese research vessel Mengxiang has recovered basalt from a deep ocean basin in the South China Sea during a trial mission. According to the China Geological Survey, this marks a new step in China’s deep-sea drilling capability; the scientific interpretation of the samples still requires further investigation.

The expedition lasted thirty days. In an area where the seabed lies about 4,100 metres below the water’s surface, two boreholes were drilled. The team reported a maximum drilling depth of 4,929.17 metres and a basalt core measuring 4.27 metres.

Mengxiang entered service in 2024 and was designed for very deep ocean drilling. During this mission, two remotely operated underwater vehicles were deployed, according to the Chinese Geological Survey. Together, they were active for more than 358 hours at a depth of about 4,000 metres.

The researchers say they processed the samples on site according to the standards of the International Ocean Discovery Program. This included recording, cutting, scanning, testing and storing the cores. The expedition involved 170 people from nine institutions, including universities and research organisations.

According to the research team, the initial observations point to several periods of large-scale volcanic activity after the spreading ridge in the South China Sea changed position. This could aid research into the formation of the basin, but the researchers themselves stress that no definitive geological conclusion has yet been reached.

In deeper layers, between about 813 and 864 metres below the seabed, the team found alternating layers of sand and clay containing organic material and traces of biological activity. Such layers may contain information about past conditions on the seabed. Laboratory analyses are needed for this, and these were not described in the news report.

China says this mission makes it the third country, after the United States and Japan, to recover hard rock from a deep ocean basin using a drillship. In the public sources consulted, that ranking is supported only by Chinese government and state-media sources.

The expedition is therefore primarily important as a technical demonstration. The samples may later provide new data on the geological development of the South China Sea, but the trial voyage itself is not a peer-reviewed research publication and does not prove a definitive new theory about the area’s formation.

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