China's ocean drilling vessel Mengxiang has returned to Guangzhou, Guangdong province, after successfully completing its first trial scientific ocean drilling expedition in the South China Sea, marking a major advance in the country's deep-sea exploration capabilities, the China Geological Survey of the Ministry of Natural Resources said on Monday.

The 30-day expedition, organized by the China Geological Survey and conducted by the Guangzhou Marine Geological Survey, operated in waters up to 4,100 meters deep. The expedition completed drilling and coring at two sites and recovered basalt samples from the South China Sea basin at one site, making China the third country in the world, after the United States and Japan, to obtain hard rock samples from a deep ocean basin using a drilling vessel.

Sun Zhen, chief scientist of the expedition and a scientist at the Guangzhou Marine Geological Survey, said the voyage marked Mengxiang's debut in scientific ocean drilling since its commissioning in November 2024.

The expedition achieved multiple breakthroughs, including advances in the 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 national record for the deepest independently conducted drilling operation, reaching a maximum operating depth of 4,929.17 meters and a maximum penetration depth of 864.77 meters below the seafloor.

Using a domestically developed rotary coring tool, the team recovered basalt core 4.27 meters in length, making China the third country to successfully use a drilling vessel to recover hard rock samples from a deep-sea basin.

"Obtaining a complete core is typically challenging. Hard rock drilling requires both advanced capabilities and technical expertise, and is a crucial indicator of 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 domestically developed equipment is very exciting," Sun said, adding that the samples will provide key evidence for testing hypotheses about the ridge jump in the South China Sea — a process in which the Earth's crust splits and shifts to a new location, forming a new ocean basin.

The trial also established a coring operation system comparable with international standards under the International Ocean Discovery Program, with multiple drilling runs achieving core recovery rates exceeding 100 percent. This means the new drilling tools can provide scientists with more continuous rock records and reduce information loss.

Coring efficiency, quality and operational stability also reached advanced international levels, while the team developed an innovative risk prevention and emergency response system for ultra-deep water and high-difficulty wells.

The expedition also deployed two remotely operated vehicles for prolonged, high-intensity collaborative operations. The vehicles accumulated more than 358 hours of underwater work at depths of around 4,000 meters, with the longest single continuous operation lasting 103 hours, demonstrating capabilities comparable to international standards.

For the first time, the team conducted a comprehensive, multiparameter analysis of core samples, covering collection, logging, cutting, scanning, sampling, testing and storage, all in accordance with International Ocean Discovery Program standards. The work demonstrated that Chinese scientists have mastered the complete operational capabilities required for ultra-deep water scientific ocean drilling.

The team discovered alternating layers of brown and green sediments during drilling, providing important geological evidence for understanding the role of natural processes in regulating climate in the ancient South China Sea environment.

The findings could also shed light on the impact of such processes on biological survival and support simulations of Earth's carbon cycle and climate regulation mechanisms, which are particularly relevant in the context of current global climate change.

At a depth of around 800 meters below the seafloor, the team discovered tens of meters of interbedded black sand and mud deposits with significant bioturbation and high organic matter content — the first such discovery in the South China Sea at depths exceeding 4,000 meters.

"Finding such rich organic matter at 4,000 meters depth was beyond our expectations," Sun said, noting that the area may have experienced periods of very rapid sedimentation and active biological activity.

Preliminary analysis of the cores also suggests multiple phases of large-scale volcanic eruptions following the ridge jump, providing important evidence for understanding the formation and evolution of the South China Sea.

There are two leading hypotheses regarding the cause of the ridge jump: one involves changes in the movements of surrounding tectonic plates, while the other points to mantle plume activity, referring to the massive upwelling of hot material from deep within the Earth. Sun said the new data appears to favor the latter hypothesis.

"This year's expedition primarily tested our drilling capabilities. A follow-up voyage next year will complete the full investigation into the ridge jump," Sun said.

(Source: ChinaDaily)