Dragon Hole: South China Sea's Oxygen-Depleted Mystery Reveals Ancient Secrets

• Scientists are examining the Sansha Yongle Blue Hole, known as the Dragon Hole, in the South China Sea, revealing new structural and chemical insights.
• The Dragon Hole reaches a depth exceeding 301 meters and is not a straight shaft, bending sideways with its lowest point over 100 meters laterally displaced from the entrance.
• Irregular shapes suggest gradual formation, likely expanding during colder periods when ocean levels were much lower, with reef limestone forming most interior walls.
• A high-grade underwater robot was deployed in 2017 to complete full three-dimensional mapping, overcoming earlier challenges with curving walls and navigation.
• Oxygen drops sharply after ninety meters, with hydrogen sulphide appearing in deeper, isolated layers, creating a natural archive of ancient climate conditions and ocean signals.