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Drastic climate changes are resposible for unavailability of 2,500 years of reef growth data

Extreme climate condition drove coral reefs to a halt which lasted thousands of years, according to a study published this week in Science.

Doctoral student Lauren Toth and Aronson, her adviser at Florida Tech, led the study of how past episodes of climate change influenced tropical reefs of the eastern Pacific. Toth, Aronson and a multi-institutional research team took core samples from reefs off the coast of Panama, estimating their age at different levels using radiocarbon dating and other methods.

The study showed how natural climatic shifts stopped reef growth in the eastern Pacific for 2,500 years. The reef shutdown, which began 4,000 years ago, corresponded to a period of dramatic swings in the El Niño-Southern Oscillation (ENSO). ENSO is the climate cycle responsible for the weather conditions every few years known as El Niño and La Niña events. "Coral reefs are resilient ecosystems," said Toth. "For Pacific reefs to have collapsed for such a long time and over such a large geographic scale, they must have experienced a major climatic disturbance. That disturbance was an intensified ENSO regime."

"As humans continue to pump greenhouse gases into the atmosphere, the climate is once again on the threshold of a new regime, with dire consequences for reef ecosystems unless we get control of climate change," said coauthor Richard Aronson, a biology professor at Florida Institute of Technology.

"We were shocked to find that 2,500 years of reef growth were missing from the frameworks," said Toth. "That gap represents the collapse of reef ecosystems for 40 percent of their total history." Toth and Aronson also examined reef records from other studies across the Pacific, they discovered the same gap in reefs in far away countries like Australia and Japan.

Scenarios of climate change for the coming century echo the climate patterns that collapsed reefs in the eastern Pacific 4,000 years ago. The reefs off Panama are on the verge of another collapse. “Even conservative models of climate change predict a return to extreme weather conditions,” said Dr. Aronson.

“This means that reefs could shut down. The hopeful part is that these reefs did prove to be resilient 1,500 years ago. Reefs today could recover, but only if we get a handle on the greenhouse gases causing climate change,”explained Dr. Aronson.
Local conditions would have to improve, too, Dr. Aronson added. “Coral mining is also a threat, ship grounding, overfishing. You have to address both the local and the global issues.”