China's ocean drilling vessel Mengxiang has recently returned to Guangzhou, Guangdong province, after successfully completing its first trial scientific ocean drilling expedition in the South China Sea, marking a major leap in the country's deep-sea exploration capabilities, the China Geological Survey of the Ministry of Natural Resources said on Monday.
The 30-day voyage, organized by the China Geological Survey and conducted by the Guangzhou Marine Geological Survey, operated in water depth of 4,100 meters. The expedition completed drilling and coring at two sites, recovering basalt samples from the South China Sea basin at one site, making China the third country in the world to obtain hard rock samples from a deep ocean basin using a drilling vessel.
Sun Zhen, chief scientist of the trial expedition and a scientist at the Guangzhou Marine Geological Survey, said the voyage represents Mengxiang's debut in scientific ocean drilling since its commissioning in November 2024.
The expedition achieved multiple breakthroughs, including advances in the scientific study of the South China Sea's tectonic evolution, the establishment of a coring system that meets international standards, and the application of domestically developed core drilling equipment, Sun said.
She noted that the expedition set a new national record for the deepest independently conducted drilling operation, achieving a maximum operation depth of 4,929.17 meters and a maximum penetration of 864.77 meters below seafloor. Using a domestically developed rotary coring tool, the team recovered 4.27 meters of basalt core, making China the third country in the world to successfully use a drilling vessel to recover hard rock samples from a deep-sea basin, following the United States and Japan.
"Obtaining a complete core is typically challenging, making hard rock drilling a task that requires both capability and technique, and serving as a crucial indicator for assessing the capabilities of ocean drilling platforms," Sun said.
She noted that basalt, while abundant on the ocean floor, is extremely hard and brittle, particularly in deep and ultra-deep waters. In the South China Sea, thick layers of sediment often cover the bedrock, requiring drillers to penetrate hundreds of meters of deposits before reaching the target rock.
"Recovering intact basalt cores with the domestic equipment is very exciting," Sun said, noting that these samples will provide key evidence to test hypotheses about ridge jump in the South China Sea — a process where the Earth's crust splits and shifts to a new location to form a new ocean basin.
The trial also saw the establishment of a coring operation system on par with the International Ocean Discovery Program, with multiple drilling runs achieving core recovery rates exceeding 100 percent. This means that the new drilling tools can provide scientists with continuous rock records and reduce the loss of information.
Coring efficiency, quality, and operational stability also reached advanced international levels, and the team developed an innovative risk prevention and emergency response system for ultra-deepwater, high-difficulty wells.
In a series of firsts, the expedition deployed two remotely operated vehicles for prolonged, high-intensity collaborative operations. These vehicles accumulated over 358 hours of underwater work at a depth of 4,000 meters, with the longest single continuous operation lasting 103 hours, showcasing capabilities comparable to international standards.
For the first time, the team performed a comprehensive, multiparameter analysis of core samples — including collection, logging, cutting, scanning, sampling, testing and storage — all in accordance with the International Ocean Discovery Program standards, demonstrating that Chinese scientists have mastered the complete operational capabilities for ultra-deepwater ocean scientific drilling.
The team discovered alternating layers of brown and green sediments during drilling, which offer crucial geological insights into understanding the role of natural processes in regulating climate change in the ancient environment of the South China Sea. These findings also shed light on their influence on biological survival and support simulations of Earth's carbon cycle and climate regulation mechanisms, which are particularly important in the context of today's global climate change.
At a depth of around 800 meters below the seafloor, the team discovered tens of meters of interbedded black sand-mud deposits with significant bioturbation and high organic matter content — the first such discovery in the deep-water South China Sea beyond 4,000 meters.
"Finding such rich organic matter at 4,000 meters depth was beyond our expectations," Sun said, noting that this area may have encountered very rapid sedimentation and active biological activity events.
Additionally, preliminary analysis of the cores suggest multiple phases of large-scale volcanic eruptions following the ridge jump, providing critical support for understanding the sea's formation and evolution. While two leading hypotheses exist — one involving changes in surrounding plate movements, and the other pointing to mantle plume activity, which is a massive upwelling of hot material from deep within the Earth — Sun said the new data appears to favor the latter.
"This year's expedition primarily tested our drilling capabilities. A follow-up voyage next year will complete the full investigation into the ridge jump," she added.
