"I've been studying the tropical Pacific Ocean for most of my career, and I had never noticed that," he said. "It jumped out at me immediately, and I thought, 'there's probably a story there.' "
So Karnauskas and Cohen began to investigate how the EUC would affect the equatorial islands' reef ecosystems, starting with global climate models that simulate impacts in a warming world.
Global-scale climate models predict that ocean temperatures will rise nearly 3oC (5.4oF) in the central tropical Pacific. Warmer waters often cause corals to bleach, a process in which they lose the tiny symbiotic algae that life in them and provide them with vital nutrition. Bleaching has been a major cause of coral mortality and loss of coral reef area during the last 30 years.
But even the best global models, with their planet-scale views and lower resolution, cannot predict conditions in areas as small as small islands, Karnauskas said.
So they combined global models with a fine-scale regional model to focus on much smaller areas around minuscule islands scattered along the equator. To accommodate the trillions of calculations needed for such small-area resolution, they used the new high-performance computer cluster at WHOI called "Scylla."
"Global models predict significant temperature increase in the central tropical Pacific over the next few decades, but in truth conditions can be highly variable across and around a coral reef island," Cohen said. "To predict what the coral reef will experience under global climate change, we have to use high-resolution models, not global models."
Their model predicts that as air temperatures rise and equatorial trade winds weaken, the Pacific
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Woods Hole Oceanographic Institution