Susan Casey (Doubleday)
DESPITE the recent tragic loss of OceanGate鈥檚 Titan submersible, people will continue to explore the ocean鈥檚 darkest corners. Susan Casey, a smart documenter of the aquatic world in her previous books The Devil鈥檚 Teeth and The Wave, helps us see why in her latest book.
The Underworld: Journeys to the depths of the ocean seeks to answer a question first posed by Aristotle as he dissected cuttlefish in the 4th century BC: what is beneath the ocean鈥檚 surface?
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The deep, it transpires, is so murky its boundaries can鈥檛 be agreed by scientists. As Casey shares her definitions for the limits of the twilight, midnight and abyssal zones, she describes how life gets stranger the deeper you go.
There are carpets of 鈥減ale gold ooze鈥� (likely to be clouds of micro-organisms) on the sea floor 600 metres down, alongside bronze cannons from the sunken Spanish galleon San Jose off the coast of Colombia. In the hadal zone 鈥� ocean trenches that extend from 6000 to 11,000 metres deep, named after Hades, the Greek god of the underworld 鈥� are dumbo octopuses (Grimpoteuthis), amphipods exuding their own armour and animals with photophores glowing like the 鈥渘uclear-blue lights of an airport runway鈥�.
This catalogue is interspersed with what attracted Casey to these habitats, including holidays by Canada鈥檚 Lake Huron, where she fed hot dogs to sturgeon. She recounts the journey that took this childhood admirer of Jacques Cousteau 鈥� the naval officer turned TV aquanaut 鈥� to scuba diving, then to free-falling in a submersible for two and a half hours in the Pacific Ocean鈥檚 abyssal realm, where the pressure is the equivalent of having 鈥�292 fully-fuelled 747s stacked on top of you鈥�. To finance this descent, she reached out to billionaires.
Exploration of the deepest regions is usually driven by a mineral gold rush or a disaster: the disappearance of flight MH370 in 2014 over the Indian Ocean, for instance, prompted a 1046-day scouring of this region of the abyss, the most thorough so far, she says.
What will future exploration find? Casey lists precious metals such as dysprosium and yttrium 鈥� used in smartphones. Then there are truly terrifying elements in sites like the bottom of the Tonga Trench, where the radioactive plutonium jettisoned in 1970 during the return of Apollo 13 is waiting.
Casey is critical of too much commercial activity on the seabed, especially as much of it is still unmapped. Already, sections are covered with litter and debris. She interviews Don Walsh, who visited the shipwrecks of the Bismark and the Titanic on a seabed so peppered with rusting debris she says it resembled 鈥渁n explosion in a boiler factory鈥�.
There are also hidden dangers in the deep. We go to the Cascadia subduction zone off the western coast of North America, where a catastrophic megathrust event occurred in 1700. This created a magnitude-9 earthquake and tsunami that devastated Japan and British Columbia. It is, she reminds us, an event that typically occurs every 300 to 500 years.
The ocean depths also hold the key to reconstructing ancient climates to better understand our own era, as well as how life might look elsewhere. Casey quotes microbiologists who have seen white spires along the vent fields of the mid-Atlantic ridge: 鈥淭his is an example of a type of ecosystem that could be active on [the moons] Enceladus or Europa right this second鈥�. How fascinating that Casey鈥檚 underworld may shed light on future off-worlds.
George Bass is a writer based in聽Kent,聽UK
