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| The Twilight Zone's Bleaching Secrets Revealed |
Imagine diving into a vibrant underwater world, teeming with coral ecosystems bursting with color. Now, picture descending deeper, into the twilight zone – a realm of dimmer light and cooler temperatures. But instead of flourishing coral, you find ghostly white skeletons - a chilling sign of an emerging threat.
This is the stark reality witnessed by marine biologist Nicola Foster and her team exploring the Chagos Archipelago's mesophotic reefs. These deeper ecosystems, once considered safe havens from rising sea temperatures, are now exhibiting the deepest coral bleaching ever recorded, raising alarms for their future.
Bleaching occurs when stressed corals expel the symbiotic algae that sustain them, leaving behind a ghostly white shell. While typically triggered by warm surface waters, Foster's 2019 observations, published in Nature Communications, reveal a different culprit: the twilight zone's own temperature shift.
At nearly 300 feet below the surface, the team encountered corals bleached in waters exceeding 84°F – far above the comfortable range for these deep-dwelling organisms. This anomaly coincided with the Indian Ocean Dipole, a climate phenomenon that disrupts normal wind and current patterns.
"The dipole essentially deepened the warm upper layer of the ocean," explains co-author Phil Hosegood, a physical oceanographer. "This exposed the corals to temperatures they wouldn't normally encounter, leading to the observed bleaching."
This discovery suggests similar events might be affecting mesophotic reefs worldwide, particularly where phenomena like El Niño cause similar thermocline deepening. While the Chagos corals displayed remarkable recovery by 2022, each bleaching event weakens them, increasing their vulnerability in the long run.
"Another Indian Ocean Dipole event began late last year, potentially threatening these reefs yet again," warns Hosegood. Understanding the precise mechanisms behind thermocline deepening and its duration is crucial for predicting and mitigating future damage.
"The data suggests that these natural cycles are being amplified by climate change," Hosegood adds, highlighting the urgency of action. "Future dipole patterns are likely to be more severe, emphasizing the need for proactive measures to protect these unique ecosystems."
Foster's team's groundbreaking discovery throws open a window into the hidden world of twilight zone reefs. It serves as a stark reminder that even the seemingly remote corners of our oceans are not immune to the challenges of a changing climate. Further research and international collaboration are critical to safeguard these irreplaceable underwater treasures.
