China’s Deep-Sea Drilling Ship Mengxiang Reaches Record Depth In South China Sea

China’s deep-sea drilling ship Mengxiang has returned to Guangzhou after completing its first scientific drilling trip in the South China Sea.

During the 30-day expedition, the ship reached 4,929.17 metres below the ocean surface and drilled 864.77 metres into the seabed. It also brought back a 4.27-metre-long piece of basalt rock.

The expedition was organised by the China Geological Survey and carried out by the Guangzhou Marine Geological Survey. The team worked at two sites in the South China Sea, where the water was about 4,100 metres deep.

The drilling set a new national record for scientific drilling. It also made China the third country, after the United States and Japan, to recover hard rock from a deep ocean basin using a drilling ship.

The samples could help scientists understand how the South China Sea formed and changed over millions of years.

Early tests of the samples suggest that large volcanic eruptions took place after a geological event called a spreading ridge jump.

A spreading ridge is a place on the ocean floor where tectonic plates move apart. Magma rises through the gap and forms new ocean crust. In a ridge jump, this spreading centre moves to another location.

Scientists are studying this process to understand how the South China Sea basin developed.

Mengxiang used a rotary drilling tool developed in China to recover the basalt core.

Getting a complete piece of basalt is difficult because the rock is hard and brittle. There are also thick layers of sediment on the seabed in parts of the South China Sea. Drilling teams therefore have to pass through the sediment before reaching the rock below.

Sun Zhen, chief scientist of the expedition and a scientist at the Guangzhou Marine Geological Survey, said getting a complete core is difficult and requires both equipment and skill.

The basalt samples will help scientists test ideas about the ridge jump and the formation of the South China Sea.

The team also set up a coring system that meets the standards of the International Ocean Discovery Program, which uses ocean drilling to study rocks and sediments below the seabed.

Several drilling runs recovered more than 100% of the amount of core expected from the drilled section. This gave researchers longer and more continuous rock samples to study.

The team also developed a system to deal with risks and emergencies during difficult deep-water drilling operations.

At about 800 metres below the seabed, researchers found alternating layers of brown and green sediment.

These layers could give scientists information about the marine environment in the distant past. They could also help them study changes in climate and biological activity in the area.

The team also found tens of metres of black sand and mud containing a large amount of organic matter and signs of biological activity.

The team made the discovery in water deeper than 4,000 metres, and it was the first of its kind reported in the deep-water South China Sea, according to the source.

Sun said the area may have experienced periods of rapid sediment buildup and active biological activity.

The samples may also help scientists study the Earth’s carbon cycle and how climate was regulated in the ancient marine environment.

The expedition included tests of two remotely operated underwater vehicles.

The vehicles worked for more than 358 hours at depths of about 4,000 metres. Their longest single operation lasted 103 hours.

The team also carried out a full process for studying the cores. This included collecting, recording, cutting, scanning, sampling, testing and storing them.

The work followed the standards of the International Ocean Discovery Program, according to the China Geological Survey.

The expedition also tested the efficiency, quality and stability of the ship’s drilling operations.

References: SCMP, China Daily