China has identified a rare coral reef blue hole within Scarborough Shoal, a hotly contested feature in the South China Sea that is now a major flashpoint in the region. A marine blue hole is a deep, circular sinkhole in the ocean and is typically bright turquoise or emerald green. Unlike most of the world’s known blue holes – which were once caves on land thousands of years ago during the last ice age – the newly discovered marine blue hole within the Scarborough Shoal lagoon was formed by the...