'Gardens and graveyards' of coral discovered in hidden canyons off Australia's coast

Coral blooming in the abyssal depths of Australia's southern coast — Coral blooms in the abyssal depths of Australia's southern coast.

(Image credit: ROV SuBastian/ SOI)

The South Australian coast is surrounded by a labyrinth of underwater canyons, many of them still unexplored. Last week, an international team of researchers (and their underwater robot companion) completed a survey of three such canyons, uncovering a hidden world of both thriving coral gardens and ash-white coral graveyards.

According to the expedition members, the fate of these hidden ecosystems, which sit in the immediate path of the increasingly warm water flowing out of Antarctica's Southern Ocean, could be a preview of how farther-flung ocean life will react to ongoing global warming.

Beyond the obvious reason for such exploration (hidden worlds are awesome), scientists are interested in these submarine crannies because they sit on the front lines of oceanic climate change. Facing the Southern Ocean — the ocean that surrounds Antarctica and connects the Atlantic, Pacific and Indian oceans with its clockwise-flowing current — these canyons are some of the first ecosystems on Earth to encounter the warming waters surging out of Antarctica's ocean.

Thanks to a mechanism called the Antarctic convergence (in which cold water flowing north clashes with warmer, south-flowing water), the currents leaving the Southern Ocean are remarkably rich in nutrients. That makes the submarine canyons of South Australia a hotspot for migrating animals. Bremer Canyon, for example, is home to the Southern Hemisphere's largest seasonal gathering of killer whales and often hosts traveling sharks, dolphins, squids and birds, the researchers said.

During their latest expedition, the crew of the Falkor learned that these canyons are bustling with life deep underwater. Each spot hosted lush gardens of coral, rich with marine life and bursting with color. However, each canyon (especially Leeuwin) also contained extensive pockets of dead and fossilized coral. According to the researchers, these corals bear the record of both recent, anthropogenic ocean warming, as well as longer-term changes to the world's climate. It's not clear yet what killed the coral in a given canyon, but researchers will begin answering that question as soon as Falkor returns to land.

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Brandon is the space / physics editor at Live Science. With more than 20 years of editorial experience, his writing has appeared in The Washington Post, Reader's Digest, CBS.com, the Richard Dawkins Foundation website and other outlets. He holds a bachelor's degree in creative writing from the University of Arizona, with minors in journalism and media arts. His interests include black holes, asteroids and comets, and the search for extraterrestrial life.