
AsianScientist (Feb. 13, 2017) – The sea level in Southeast Asia fluctuated wildly more than 6,000 years ago, even without the influence of climate change caused by humans. These results, published in Nature Communications, come as a warning to the 100 million people who live within three feet of sea level in the region.
“This research is a very important piece of work that illustrates the potential rates of sea-level rise that can happen from natural variability alone,” said Benjamin Horton, a professor at Rutgers University. “If a similar oscillation were to occur in East and Southeast Asia in the next two centuries, it could impact tens of millions of people and associated ecosystems.”
To delve into the region’s past, a team led by Dr. Aron Meltzner from the Earth Observatory of Singapore at Nanyang Technological University used coral microatolls to understand when, and by how much, the sea level had risen and fallen near the Indonesian island of Belitung, which lies between Sumatra and Borneo.
A microatoll is a circular coral colony, typically no more than about 20 feet across, in which the topmost coral is dead and the bottom part living and growing. By taking samples from microatolls in different places, scientists can date rises and falls of sea level. The microatolls are what scientists call a “proxy”—a natural process that provides a reliable record of past events.
“In any region, you try to find the proxy controlled by sea level,” Horton said. “In New Jersey, we have no corals, so we use salt marshes. In the tropics, corals are the go-to proxy.”
The scientists studied microatolls at two sites on opposite sides of the island and found that the relative sea level rose twice in the period from 6,850 years ago to 6,500 years ago. That this oscillation took place without any human-assisted climate change suggests that such a change in sea level could happen again now, on top of the rise in sea level that is already projected to result from climate change. This could be catastrophic for people living so close to the sea.
Meltzner said they didn’t expect the fluctuations they found because those changes in sea level contradicted what they knew about sea level in Southeast Asia.
“Our conventional understanding of ocean circulation and ice-melting history told us that such fluctuations should not occur, so we were a bit mystified at the results from our first site,” Meltzner said.
“But after finding a similar pattern at a second site 80 kilometers to the southeast, and ruling out other plausible explanations, it was clear that the coral growth patterns must reflect regional changes in sea level. There would be way too many coincidences otherwise.”
The paper comes out of a long-running research project aimed at understanding the physical processes involved in sea-level rise. Such understanding is necessary to help scientists understand the present and likely future state of the ocean.
“This is a basic science problem,” said study co-author Professor Robert Kopp. “It’s about understanding past changes. Understanding what drove those changes is what allows us to test the climate models we use to predict future changes.”
The article can be found at: Meltzner et al. (2017) Half-meter Sea-level Fluctuations on Centennial Timescales from Mid-Holocene Corals of Southeast Asia.
———
Source: Rutgers University; Photo: Aron Meltzner/NTU.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.