China and Indonesia have completed their first joint scientific expedition in the Java Trench, located in the Indian Ocean. The scientific research vessel Tansuo-1 (Discovery One), carrying the deep-sea manned submersible Fendouzhe (Striver), returned to Sanya City, south China's Hainan Province, on Thursday.

The joint scientific expedition was conducted by the Chinese Academy of Sciences (CAS) and Indonesia's National Research and Innovation Agency.

The expedition team, consisting of experts from 11 universities and institutions from the two countries, set sail from Sanya on February 8 for a 50-day voyage of deep-sea diving missions into the Java Trench.

The manned submersible Fendouzhe completed 22 dives in the trench, 14 of which reached a depth of more than 6,000 meters. The scientists jointly completed a diving mission at the deepest point in the trench at 7,180.4 meters, setting the deepest dive record for Indonesia.

Samples of macrobenthos, rocks and sediments have been collected, and high-definition videos and photographs were taken during the missions. 

It was the first large-scale and systematic manned deep-sea exploration conducted in the Java Trench at an international level.

"We discovered two active low-temperature hydrothermal vent sites in the Java Trench, where low-temperature hydrothermal vent fluids serve as valuable food and energy sources for benthic organisms. We also observed iron oxide-rich sediment layers at the trench bottom," said Du Mengran, a research fellow at the CAS Institute of Deep-sea Science and Engineering.

"These findings significantly enhance our understanding of the unique geologic activities and biodiversity in the area, as well as the co-evolution of geology and life," said Du.

The joint expedition has opened a new chapter for strengthening maritime cooperation between China and Indonesia. It will further deepen the understanding of the geological process in the abyssal zone and the evolution of the Earth.