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Ought Six
04-15-2009, 09:58 PM
Fossil Corals Show Catastrophic Sea-Level Rise? (http://news.nationalgeographic.com/news/2009/04/090415-sea-levels-catastrophic.html)


Brian Handwerk
National Geographic News
April 15, 2009


Fossil coral reefs at a Mexican theme park "confirm" that sea levels rose rapidly about 121,000 years ago, according to a controversial new study.

Previous research on fossil reefs had shown that sea levels surged by 13 to 19 feet (4 to 6 meters) near the end of the last time period between ice ages, known as an interglacial period. But researchers have been unsure whether this sea-level rise happened quickly or gradually.

By mapping the ages and locations of ancient corals at Xcaret, an eco-park in the Yucatán Peninsula, Paul Blanchon of the National Autonomous University of Mexico, and colleagues, were able to chart when the reefs died and were replaced by others on higher ground.

Their data suggest that sea levels rose by about 10 feet (3 meters) in 50 years—much faster than the current annual rate of 0.08 to 0.1 inch (2 to 3 millimeters).

Because this event happened during an interglacial period—similar to the one we're in currently—the find boosts the chances that today's melting ice sheets could trigger rapid sea-level rise, the study authors say.

But not all experts on corals and climate are convinced by the new study.

Tad Pfeffer, of the University of Colorado at Boulder, noted that Blanchon's team couldn't directly measure the rate of sea level change around the Mexican corals, because the age estimates aren't accurate enough.

Instead the study authors compared changes seen in Xcaret to those seen in reefs with well-established ages in the Bahamas.

"It's an interesting idea, but one that for me is only suggestive and not compelling," Pfeffer said.

"I'd want to see something more solid than this if I'm going to buy the idea of such rapid sea level rise at the time [of the last interglacial]."

Even if the new study is confirmed, Pfeffer added, more research would be needed to determine if rapid sea-level rise 121,000 years ago provides evidence that similar changes can happen now.

"And of course, when would 'now' be?" he asked.

"'In the next few decades' vs. 'the next few thousand years' are both 'now' on the time scales at which glacial and interglacial periods are defined, but are very different situations in terms of how we determine responses."

Mike Kearney, of the University of Maryland, said it's "within the realm of possibility" that global warming will trigger a sudden collapse of the West Antarctic ice sheet, which could lead to a rapid increase in sea levels like that predicted by the new study.

"But the big unknown is whether any of the things we think we know about the Antarctic ice sheet prove to be true," Kearney cautioned.

"One camp says [rapid sea-level rise] could happen, another camp says it would take thousands of years. I'm not sure what the conventional wisdom is right now. It depends on who you talk to."

Findings appear in this week's issue of the journal Nature.