Much like tree rings, corals form annual growth bands that are preserved for millennia. As corals grow, they track changes in sea level in great detail, making them ideal recorders of relative sea level over time.
Studying millennia-old coral microatolls on the Indonesian island of Belitung, an international research team led by Asst Prof Aron Meltzner and Assoc Prof Adam Switzer from NTU’s Earth Observatory of Singapore found that sea levels in Southeast Asia oscillated by up to 60cm over the course of a few centuries about 6,500 to 6,800 years ago.
By analysing recordings from two sites on Belitung Island and from a third site in South China, the team detected two separate time periods—about 6,750 years and 6,600 years ago— when sea levels were about 60cm above that of an intermediate period about 6,700 years ago.
Though they have yet to pinpoint the specific climatic conditions behind these historic sea-level fluctuations, the researchers note that an extra 60cm rise in sea levels—on top of the globally predicted rise—would have a considerable impact on surrounding shores.