QINGDAO, June 23 (Xinhua) -- Chinese submersible Jiaolong returned to the national deep sea center at east China's Qingdao on Friday, ending a four-month expedition.

The submersible made 30 dives during the country's 38th oceanic scientific expedition and descended to nearly 6,700 meters in the Yap Trench in the west Pacific, close to its record depth of 7,062 meters in 2012.

Scientists have gained a lot of precious samples and data in this expedition, including samples of rocks, large marine life, two lion fish and two unknown species.

They also reached a better understanding of deep sea hydrothermal movement in the Indian Ocean, and conducted surveys in the South China Sea that will help multi-metal nodule mining tests.

The expedition started in February and its completion also marks the end of the submersible's four-year trial phase.