Huangyan Island Blue Hole: A New Window Into South China Sea Climate History
When China’s Ministry of Ecology and Environment (MEE) released the 2025 Survey Report on Huangyan Dao Blue Hole on June 25, the announcement of a rare coral reef growth-structure type marine blue hole in the South China Sea captured global attention. But beyond the headline discovery lies a scientific treasure with far-reaching implications for understanding climate history, sea-level change, and marine biodiversity in one of the world’s most contested and ecologically significant maritime regions.
A Geological Archive Spanning Millennia
Marine blue holes are among Earth’s rarest geological formations — deep, circular depressions on the ocean floor often called the “Eye of the Ocean” for their striking deep-blue appearance. According to the MEE official announcement, the newly identified blue hole in the lagoon of Huangyan Island (Scarborough Shoal) is only the second known example of a coral reef growth-structure type worldwide, joining Australia’s Houtman Abrolhos Blue Hole.
What makes this discovery particularly significant for climate science is its age. Radiocarbon-14 isotope dating has established that the blue hole formed at least 3,200 years ago, placing its origin in the mid-to-late Holocene epoch — a period critical for understanding modern climate patterns. As the Xinhua News Agency reported, the structure serves as a “natural archive” of geological environmental evolution, historical climate records, and biodiversity changes.
“The Huangyan Island blue hole is a key geological archive for recording the paleo-environmental evolution of the South China Sea, sea-level fluctuations, and the impacts of global and regional climate change,” states the 2025 Survey Report on Huangyan Dao Blue Hole, as cited by the MEE full report page.
A Biodiversity Hotspot Revealed
The blue hole’s scientific value extends well beyond geology. Field surveys conducted over two years in the surrounding waters have recorded extraordinary biodiversity: 165 species of hard corals belonging to 14 families and 44 genera, and 184 species of fish from 27 families and 85 genera, according to China Daily. Using environmental DNA (eDNA) technology, scientists detected over 2,700 marine species in the area.
Notable inhabitants include the green sea turtle (Chelonia mydas), a Class I nationally protected wildlife species in China, observed inhabiting the blue hole and its surrounding waters. The survey also recorded the first field observation of the bear paw clam (Hippopus hippopus) in Huangyan Island waters, found exclusively in the shallow water of the blue hole’s sidewall.
Professor Yu Kefu from the Guangxi Laboratory on the Study of Coral Reefs in the South China Sea at Guangxi University told the Global Times that the blue hole can offer important information for studies on biodiversity in the South China Sea and the evolution of coral reef biota in the Indo-Pacific convergence zone. “By learning from the past to better understand the future, these studies can provide important scientific support for humanity’s response to global change,” he said.
Formation: A Unique Coral Reef Process
Unlike the more common limestone dissolution-type blue holes — such as Belize’s Great Blue Hole or China’s own Sansha Yongle Dragon Hole (the world’s deepest at 300.89 meters) — the Huangyan Island blue hole formed through an entirely different mechanism. Scientists believe it developed in a high-density patch reef area within the lagoon, where adjacent pinnacle reefs grew over time under the influence of climate change and sea-level fluctuations, eventually expanding laterally and cementing together to form the closed structure.
The blue hole measures 56.3 meters in diameter at its surface opening, with a depth of 16.6 meters and an opening area of approximately 1,491.7 square meters. Its funnel-shaped internal structure and observed turbidity stratification within the water column provide additional clues about its formation and ongoing ecological dynamics.
Conservation and Geopolitical Dimensions
The discovery provides strong scientific justification for the Huangyan Island National Nature Reserve, established by the Chinese State Council in September 2025 — months before the blue hole report’s release. MEE spokesperson Pei Xiaofei emphasized that the survey results “highlight the positive achievements of ecological protection in the waters of Huangyan Island,” as reported by People’s Daily.
The release of the report in both Chinese and English, alongside a CGTN-produced video titled “Eye of the South China Sea — Huangyan Island Blue Hole,” reflects an intentional effort to present China’s scientific activities in the disputed waters as transparent and internationally engaged. International media, including Pakistan’s The News International, have covered the discovery as a scientific achievement.
Ding Duo, director of the Research Center for International and Regional Studies at the National Institute for South China Sea Studies, told the Global Times that the ecological surveys conducted at Huangyan Dao represent “concrete examples of China’s lawful exercise of territorial sovereignty and maritime jurisdiction.”
The Road Ahead
The MEE’s South China Institute of Environmental Sciences, in collaboration with other research institutions, plans to conduct more comprehensive investigations focusing on the blue hole’s formation mechanisms, ecological evolution patterns, ecosystem functions, and its role in sustaining the high biodiversity of the Huangyan Island ecosystem. These studies aim to provide scientific support for further strengthening ecosystem and biodiversity conservation in the South China Sea.
As only the second known coral reef growth-structure type blue hole worldwide, the Huangyan Island discovery opens new avenues for understanding these rare geological formations and the unique ecosystems they support. For climate scientists, the 3,200-year sedimentary record preserved within its depths offers a rare opportunity to reconstruct environmental changes in the South China Sea with a precision that few other natural archives can match.