Groundbreaking Study Reveals Alarming Depths of Coral Bleaching due to Global Warming in the Indian Ocean
Tools and fire were once seen as fortunate advancements for ancient humans. However, as our technology has evolved, we have been left to deal with the consequences of our actions, even in seemingly untouched places like space and the deep ocean. As our influence spreads across the planet, the list of unaffected areas continues to shrink.
In a groundbreaking study, researchers have made a shocking discovery – evidence of coral bleaching at depths previously thought to be immune to the effects of global warming. The team found that up to 80% of certain reef areas 90 meters below the surface of the Indian Ocean were impacted, likely due to a significant rise in sea temperatures.
Deteriorating Conditions for Marine Ecology
Increased heat stress has led to bleaching in 75% of the world’s tropical coral reefs in recent years. Scientists estimate that 70-90% of these reefs will be lost with a 1.5°C increase in global warming, and complete bleaching will occur if temperatures rise beyond 2°C. However, until now, it was believed that these impacts were limited to shallower regions.
Published in the prestigious scientific journal Nature, a recent study presents the first evidence of coral bleaching in deeper coral reefs. The team attributes the spike in temperatures to the positive state of the Indian Ocean Dipole (IOD) in 2019.
The IOD refers to a temperature difference between the eastern and western parts of the Indian Ocean. A positive IOD, often associated with the El Niño phase in the Pacific Ocean, results in warmer than average water in the western parts of the Indian Ocean and enhances monsoon rainfall in India. However, the increasing frequency and intensity of positive IOD events have spelled disaster for deep corals.
Dr. Phil Hosegood, the project lead, expresses surprise at the findings, stating, “There are no two ways about it; this is a huge surprise. Deeper corals had always been thought of as being resilient to ocean warming because the waters they inhabit are cooler than at the surface and were believed to remain relatively stable.”
The deep coral reefs house a significant amount of marine biodiversity, supporting approximately 25% of known marine species. Coral bleaching disrupts the symbiotic relationship between corals and algae, limiting their ability to support diverse marine life. Such events pose a threat to the entire marine ecosystem of the region.
Ocean Warming Takes the Blame
During a research cruise in November 2019, the first evidence of coral damage was observed when remotely operated underwater vehicles captured images of bleached corals. Surprisingly, no visible harm was detected in the shallow water reefs of the region.
Analysis revealed that a deepening thermocline, driven a positive IOD, caused the bleaching in deeper reefs. In simpler terms, while the temperature at the ocean’s surface remained stable, temperatures beneath the surface rose significantly, making it challenging for organisms to adapt.
Scientists had previously relied on deep-water corals, found at depths between 30-150 meters, to compensate for the decline in shallower reefs. However, this new study suggests that even these deep reefs are vulnerable to bleaching. The lack of research in deep ocean exploration further complicates the situation.
Fortunately, the team observed that many parts of the reef managed to recover during subsequent research expeditions in 2020 and 2022. However, the authors caution that the situation is far from resolved. With oceans warmer than ever, another ongoing positive IOD phase, and a powerful El Niño looming, conditions could worsen for the Indian Ocean reefs.
Dr. Hosegood emphasizes the urgency of expanding our understanding of the impacts caused these environmental changes. As global change accelerates, it is crucial to gain more knowledge about these environments that remain relatively unexplored.
The research findings are published in Nature Communications and can be accessed here.