Ancient clams give clue to climate change in South China Sea

Climate change is having a "bipolar" effect in the South China Sea, warming waters up to three times faster in winter than in summer, mainland scientists say.

The researchers reconstructed sea temperature records going back 2,500 years by using fossilised samples of Tridacnidae, giant clams that lived on reefs and grew up to 1.3 metres long.

They found the speed of temperature rises "elevated" in winter while somewhat "depressed" in summer and that the differences were far more "lively" than previously known.

That was bad news for some marine creatures, said Dr Yan Hong, associate researcher with the Chinese Academy of Sciences' Institute of Earth Environment and lead scientist of the study, published in Earth-Science Reviews. Some fish species need a significant temperature drop to lay their eggs, as cooling waters helped nutrients to rise.

"Exceptionally warm winters might disrupt this … and upset the delicate balance of marine ecology. Many species, ranging from big fish to microorganisms, could suffer," Yan said.

Warmer winters could also threaten humans by depleting fisheries and worsening air pollution. "The impact of climate warming could be stronger and more profound than previously thought," he said.