Scientists at the National Center for Atmospheric Research (NCAR) have successfully used an extremely high-resolution computer simulation of ocean circulation to identify possible “thermal refugia” where these biodiverse ecosystems are more likely to survive as ocean temperatures rise.
The research team has created an interactive, freely accessible online global atlas that shows the locations of these areas, where ocean dynamics and cooler waters combine to provide potential havens for coral reefs.
“We hope that this work serves as a starting point for other scientists interested in reefs,” said NCAR scientist Scott Bachman, who led the new study, which was published in Frontiers in Marine Science. “We invite researchers to visit our website, identify potential refugia, and then go observe the reef’s health.”
The research was funded by the National Science Foundation, which also serves as NCAR’s sponsor. Scientists from the University of Tasmania and the University of Auckland collaborated on the study.
Coral reefs are not doing well, and we’ve all been in mourning. This study focuses on areas where there is reason for optimism. We’re not claiming that this atlas will solve everything, but it will help us be smarter about conserving the reefs that have the best chance of survival.
Scott Bachman
Waves of cooler water
Climate change is threatening coral reefs all over the world, with warming ocean waters bleaching the reefs and leaving behind lifeless skeletons. The loss of coral reefs has far-reaching consequences for the environment and society. They are home to nearly one-third of all marine species and provide employment for hundreds of millions of people worldwide. According to NCAR scientist and study co-author Joan Kleypas, reefs have a global economic value of $10 trillion per year, and the protection they provide to shorelines from storm and flood damage is worth billions of dollars each year.
Scientists have discovered, however, that some reefs fare better than others. Cooler water lifted from the deep ocean by subsurface oscillations known as internal ocean gravity waves, for example, can lap over reefs and protect them from increased heat in some areas of the ocean.
“These gravity waves are everywhere, and under certain conditions, they can bring cooler water close to the ocean’s surface, where reefs are,” Bachman explained. “You need powerful waves with large amplitudes colliding with physical obstacles, such as a seamount, to force the waves upwards.”
Scientists have understood for some time that this gravity wave phenomenon exists in select places. For example, a combination of the tides and the deep basins of the Coral Triangle — a marine area that includes the waters of Indonesia, Malaysia, the Philippines, and other nearby countries — create conditions that favor gravity waves bringing cooler water to the surface. But it has been difficult to determine all the places across the globe where similar conditions could exist, in part because the gravity waves may not bring the water all the way to the surface and therefore cannot be identified by satellites.
Because scientists cannot observe thermal refugia from space, they must rely on computer modeling to identify them globally. The main challenge for models is scale. Coral reefs are small in comparison to the vastness of the ocean, and running a simulation at high enough resolution across the entire globe to capture how gravity waves interact with a specific reef necessitates massive computational resources.
However, one such simulation exists. NASA’s Estimating the Circulation and Climate of the Ocean (ECCO) Project simulated the entire ocean at a resolution of about 2 kilometers and saved data at hourly time steps, frequent enough to accurately capture how internal gravity waves behave. To do the analysis that was necessary to identify thermal refugia, Bachman downloaded a staggering 400 terabytes of data from the ECCO Project.
“This type of study is not uncommon on a local scale,” Bachman said. “However, it’s rare on a regional scale, and it’s never been done on a global scale before.” According to Kleypas, who has pioneered research into the effects of climate change on coral reefs, the resulting atlas offers some hope.
“Coral reefs are not doing well, and we’ve all been in mourning,” Kleypas said. “This study focuses on areas where there is reason for optimism. We’re not claiming that this atlas will solve everything, but it will help us be smarter about conserving the reefs that have the best chance of survival.”
