Corals construct their skeletons from calcium carbonate, releasing carbon dioxide as a byproduct.
Reinhard Dirscherl/Alamy
For the last 250 million years, coral reef systems have been crucial to the Earth’s climate, but perhaps not in the manner you might assume.
Coral reefs generate excess carbon dioxide because the formation of calcium carbonate, which constitutes coral skeletons, involves the release of greenhouse gases.
Certain plankton species utilize calcium carbonate to form their shells, and when these organisms perish, the mineral becomes buried on the ocean floor. In ecosystems dominated by coral, calcium and carbonate ions that typically nourish deep-sea plankton are rendered inaccessible.
Tristan Salles and his team at the University of Sydney conducted a modeling study on the interactions among shallow corals and deep-sea plankton over the last 250 million years, incorporating reconstructions of plate tectonics, climate simulations, and variations in sediment contribution to the ocean.
They determined that tectonic activity and geographic features foster periods with extensive shallow continental shelves, which provide optimal conditions for reef-building corals, thereby disrupting the coral-plankton dynamics.
As the area covered by coral reefs diminishes, calcium and alkali levels accumulate in the ocean, enhancing plankton productivity and increasing the burial of carbonate in the deep ocean. This shift contributes to lower CO2 concentrations and cooler temperatures.
The study revealed three significant disruptions in the carbon cycle over the past 250 million years. During these events—specifically in the Mid-Triassic, Mid-Jurassic, and Late Cretaceous—extensive coral reefs consumed vast amounts of calcium carbonate, resulting in notable ocean temperature increases.
Once the balance between shallow-sea corals and deep-sea plankton is disrupted, realignment can require hundreds of thousands to millions of years, noted Salles.
“Even if the system recovers from a significant crisis, achieving equilibrium will be a prolonged process, significantly extending beyond human timelines,” Salles elaborated.
On a brighter note, Salles observes that corals excel at absorbing excess nutrients to aid in reef building, even if planktonic nutrient growth gets excessive.
Currently, human-induced carbon dioxide emissions are driving unprecedented global warming and ocean acidification, endangering both corals and plankton, according to Salles. While the outcomes remain uncertain, the potential impact on ecosystems could be catastrophic.
“The feedback mechanisms we modeled span deep time and may not be relevant today. The current rate of change is too rapid for carbonate platform feedbacks to maintain similar significance.”
Alexander Skiles from the Australian National University in Canberra remarks that this research illustrates a “profoundly interconnected feedback cycle between ecosystems and climate.”
He suggested that while species are presumed to evolve and adapt to the climatic conditions dictated by “immutable physical and chemical processes,” it is increasingly evident that certain species are actively shaping the climate itself, leading to co-evolutionary feedback loops.
“Beyond corals, ancient microbial colonies like stromatolites have significantly influenced atmospheric carbon regulation,” Skiles pointed out.
“It is well-recognized that carbon is accelerating climate warming at an alarming rate. Corals contribute to this dynamic over extensive geological time, which may elucidate fluctuations between warmer and cooler periods.”
Source: www.newscientist.com
