Jack checked the computer projections – the heat was just under a hundred degrees outside now, and climbing to two hundred deeper down. “You’re probably right. Let’s stay close to the canyon wall, and drop down just enough to clear the ceiling. We pass under it, and then take her back to shallower water. Hopefully, we can find another air pocket once we pass through.”

Yegor grunted his assent, and eased the wheel forward.

“Cate, can you come up here.” Jack nodded her forward.

Cate left her seat and bent towards his face. “What is it?”

Jack momentarily smelled her perfume. He lowered his voice. “Getting damned hot – inside and out. Not sure how hot it’s going to get, and we need to dive even deeper under the ceiling.” His eyes flicked to Greg and Abby. “Things are getting a little tight, and I don’t want claustrophobia starting to crowd us.”

Cate nodded. “Don’t worry; I’ve got some of my best travelling songs set to go.”

“That’s the spirit.” Jack grinned. “But no dancing.”

She crouched. “But this answers a few questions though. The main one being why there’s so much life in this sunless water –the heat, and the minerals from whatever geothermal activity below are the basis of a food chain.”

“I know, I’ve dived to thermal vents that support abundant hydrothermic communities miles down in the deep. The extremophile bacteria form huge mats near the hot vents, which attracts organisms such as amphipods and copepods that graze upon it. Larger organisms, feed on them, and so on, until you have a fully-functioning food chain. The things down here don’t need sunlight; they just need warmth.”

“There’s something else that bothered me,” Cate said. “Most everything we’ve seen has pigmentation, and eyes. Why would you still need eyes after so many millions of years if you lived in total darkness?”

“Yeah, I wondered that. The bioluminescent guys need them, but everything else?” He nodded. “Good question; either these things get exposed to sunlight, or there’s another light source we haven’t seen yet.”

“At five thousand feet – maximum depth,” Yegor said. “Also, we are at cave ceiling depths, and can pass under the overhang.”

“Good; steady as she goes.” Jack flexed his fingers for a moment. “We’re still on silent running folks.”

He switched on the spotlight beam, and angled it upwards. He couldn’t help grinning in awe – it gave him a weird sensation, seeing what looked like a rocky sea floor hanging over their heads. Crags, ravines and jagged rock teeth reached downwards, some for a hundred feet, and Yegor deftly maneuvered in and amongst them. Dots of small, spindly crustaceans clung on tight, and ribbons of kelp-like plants hung like drab streamers. Jack momentarily angled the light downwards, but below, there was nothing but an endless dark void.

“How deep here?” Mironov’s soft words floated from the back of the cabin.