‘Doomed’ Corals to Face Worst Bleaching in Decades

Researchers recently pieced together a vast puzzle of chemical and weather logs found deep within the skeletons of tropical corals in a famous Pacific archipelago. The result was a stunning warning about the near-future: a bleaching event is coming, and it may be the worst seen in at least 20 years.

Corals "bleach" when they become over-stressed. This usually occurs in the wake of uncharacteristically warm temperatures in coral habitat or sudden spikes in ocean acidification and causes the unique animals to expel the algae that symbiotically live within their flesh. This not only makes the corals look fuzzy and pure white, but it also severely weakens them. Without their algae friends to keep their skeletons calcified and healthy, the corals become brittle. Overstressed, exposed coral flesh also becomes increasingly vulnerable to disease.

A recent report from United Nations investigators estimated that warming ocean climes, ocean acidification, and the resulting bleaching events will cost the world economy over a trillion dollars in various resources and services by 2100.

That estimate was based on the idea that the rate of climate change and ocean acidification (caused by rising carbon levels) stayed as it is now.

However, what if natural ocean temperature cycles came to exacerbate this problem? According to a study recently published in the journal Nature Geoscience, a change in Pacific trade winds that occurs every two to three decades is nearly upon us, and its unlucky timing may lead to one of the worst bleaching events ever seen.

"When winds weaken, which they inevitably will, warming will once again accelerate," Diane Thompson, who led the study at the National Center for Atmospheric Research, recently told Scientific American.  "The warming caused by greenhouse gases and the warming associated with this natural cycle will compound one another."

Thompson and her colleagues closely analyzed clues found within the skeletons of coral growing at the Tarawa Atoll in Kiribati. Like tree rings tell about the history of rainfall, the calcification of coral skeleton can cryptically speak of decades of temperature patterns, and Thompson's team believes they have determined how to understand it. (Scroll to read on...)

Unfortunately, that understanding has painted a very bleak picture for tropical conditions. The researchers found evidence of weak trade winds early in the 20th century. Those winds coincided with a period, from 1910 to 1940, when global temperatures rose faster than could have been caused by greenhouse gas pollution alone. They suspect that history is due to repeat itself soon.

Amazingly, this study isn't the first to warn of encroaching temperature spikes in the Pacific. Another Kiribati core analysis published in the journal Paleoceanography back in November detailed how the tropical region is due for another cycle of warm-water El Niño events, which occur every two to seven years.

"The trend is unmistakable," said lead author Jessica Carilli. "The ocean is primed for more El Niño events."

However, it remains unclear how the aforementioned dying trade winds will affect this trend, and may exacerbate the problem for corals.

Mark Eakin, a coordinator at the NOAA's Coral Reef Watch program, recently told Mashable that this perfect storm of bleaching conditions may already be starting.

"Not only are we seeing more thermal stress ... but we're making [corals] more sensitive at the same time (through heightened carbon levels)," he said.

"We're seeing rising background temperatures - we're seeing this increase in the thermal content of the oceans and as that happens it doesn't take as nearly as big of an event to set off a chain of bleaching," Eakin added.

The result, the expert says, would be a bleaching event that could put our last largest event (the largest in 20 years) to shame.

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