La Niña-like conditions in the Pacific Ocean are closely linked to an abrupt stoppage of coral growth that lasted thousands of years. Will today’s climate push reefs to another collapse?
For a new study, researchers traveled to Panamá to collect a reef core, and then used the corals within the core to reconstruct what the environment was like as far back as 6,750 years ago.
The findings show that cooler sea temperatures, greater precipitation, and stronger upwelling were evident about 4,100 years ago when reef accretion in the region suddenly stopped.
Coral collapse triggers
“Investigating the long-term history of reefs and their geochemistry is something that is difficult to do in many places, so this was a unique opportunity to look at the relationship between reef growth and environment,” says Kim Cobb, associate professor in the School of Earth and Atmospheric Sciences at Georgia Institute of Technology.
“This study shows that there appears to have been environmental triggers for this well-documented reef collapse in Panama.”
Climate change is the leading cause of coral-reef degradation. The global coral reef landscape is now characterized by declining coral cover, reduced growth, and calcification, and slowdowns in reef accretion.
The new data will help scientists understand how changes in the environment trigger long-term changes in coral reef growth and ecosystem function—a critical challenge to coral-reef conservation.
Cool and wet
“Temperature was a key cause of reef collapse and modern temperatures are now within several degrees of the maximum these reefs experienced over their 6,750 year history,” says lead author Lauren Toth, who was a graduate student at Florida Institute of Technology during the study.
“It’s possible that anthropogenic climate change may once again be pushing these reefs towards another regional collapse.”
For the study, published in Nature Climate Change, researchers analyzed a 6,750-year-old coral core from Pacific Panamá. They then reconstructed the coral’s past functions, such as growth and accretion (accumulation of layers of coral), and compared that to surrounding environmental conditions before, during, and after the 2,500-year hiatus in vertical accretion.
“We saw evidence for a different climate regime during that time period,” Cobb says. “The geochemical signals were consistent with a period that is very cool and very wet, with very strong upwelling, which is more like a modern day La Niña event in this part of the Pacific.”
Sensitive to change
In Pacific Panamá, La Niña-like periods are characterized by a cold, wet climate with strong seasonal upwelling. Due to limited data at the site, researchers can’t quantify the intensity of La Niña events during this time, but document that conditions similar to La Niña were present.
“These conditions would have been for quite an extended time, which suggests that the reef was quite sensitive to prolonged change in environmental conditions,” Cobb says. “So sensitive, in fact, that it stopped accreting over that period.”
Future climate change, similar to the changes during the hiatus in coral growth, could cause coral reefs to behave similarly, the study suggests, leading to another shutdown in reef development in the tropical eastern Pacific.
“We are in the midst of a major environmental change that will continue to stress corals over the coming decades, so the lesson from this study is that there are these systems such as coral reefs that are sensitive to environmental change and can go through this kind of wholesale collapse in response to these environmental changes,” Cobb says.
Future work will involve expanding the study to include additional locations throughout the tropical Pacific.
“A broad-scale perspective on long-term reef growth and environmental variability would allow us to better characterize the environmental thresholds leading to reef collapse and the conditions that facilitate survival,” Toth says.
“A better understanding of the controls on reef development in the past will allow us to make better predictions about which reefs may be most vulnerable to climate change in the future.”
The Geological Society of America, the American Museum of Natural History, and the Smithsonian Institution’s Marine Science Network supported the study.
Source: Georgia Tech