Mercer felt he was on the trail of that first scrap of evidence he needed. “Can we check temperatures at the base of the tower?” he asked Jervis.
“No problem. Remember,
“C.W., stay here,” Mercer ordered, gripped by excitement. He was pretty sure he knew what they’d found. There was a measure of risk staying this close to the tower, but he felt justified. “We’re going to need you when we come up. I want to open up one of the propeller’s housings to see what’s inside.”
“I’ll work at it while you’re down,” C.W. said in his surfer drawl.
“No. Wait for us to come back.”
“Oh, sure, man,” he said, chastened by Mercer’s sharp tone.
Alan Jervis eased the sub away from the tower and sent the craft toward the bottom again. “What are you thinking?” he asked after they’d sunk through a thousand feet.
“Turbines can be used for three things,” Mercer said. “Pumping something up, injecting something down or generating electricity. There aren’t any transmission lines so this rig isn’t producing power. We didn’t find any reservoirs to hold something being pumped from the seafloor. That leaves us something being pumped down into the ground.”
“Makes sense, but wouldn’t there be reservoirs of whatever was being injected?”
“Not if it were seawater. Or if the system was a closed loop.”
“Which one do you think it is?”
“In a sense, both.”
“You gonna explain that?”
“Ever wonder how they keep hockey rinks frozen?”
Jervis chuckled. “I grew up in Arizona. Hockey wasn’t much of a priority.”
“The Coyotes play in Phoenix,” Mercer pointed out. “It’s done by pumping salty water — brine — through a system of tubes under the ice. Because of the salt, the brine remains liquid below thirty-two degrees. The supercold pipes keep the ice frozen and voila, slap shots in the desert.”
“Hold on,” Jervis interrupted, “we’re coming up on the bottom. The water temperature’s dropping faster than it should. It’s down four degrees in just fifteen feet.”
The lattice of struts and supports near the tower’s base wouldn’t allow them to get close to the pipes coming down from the turbine housings. Instead Mercer had Jervis circle the structure in ever-widening loops. Revealed under the lights, the bottom appeared featureless. The silt had a green cast in the artificial glow, and the blizzard of drifting organic material made it impossible to see more than a few feet. Still, Alan maneuvered the sub like an expert, keeping her nose scant feet above the abyssal plain.
“What’s that?” he asked after a few moments. “A crater?”
“Not sure,” Mercer said, but he was.
It took several minutes to cross over the crater from rim to rim. The bottom-profiling sonar showed it was a hundred feet deep. Mercer did the figures in his head. The crater had a volume of almost half a million cubic feet. He asked the pilot to hover at the edge of the large pit.
“What are we looking for?”
“Just hold it steady.” Mercer took hold of the manipulator controls.
“Hey, you can’t do that!” Jervis protested as the arms unfolded from their stowed position.
Mercer flexed them out straight, testing how his movements on the joysticks affected the joints and grapplers. “I’ll pay for any damage.”
In seconds he had the system figured. Like the controls for C.W.’s diving suit,
“What’s going on down there?” McKenzie called over the comm.
“I want a soil sample,” Mercer said.
He eased the grapple hand into the ooze, causing a small avalanche of mud to slide below the submersible. Although there was no feedback resistance on the joysticks, Mercer could tell the arm hit something solid. A silvery bubble burst from the mud, and in the cavity he’d excavated he could see a strange white mass.
“What is that?” Jervis asked.
“Ice.”
“What? That’s impossible.”
Mercer turned to look at the pilot. “And yet there it is. The rig is a giant heat pump.”
“What for? This thing doesn’t make any sense.”
“Hey, guys,” C.W. called from above, his voice metallic from the echo within his suit. “Something’s happening up here. The blades are starting to turn. Wow.”
“What is it?” Alan asked quickly.
“Current can’t be more than a knot or two, but this thing’s spinning like it’s in a freaking hurricane.”
It took Mercer a second too long to digest what C.W. had just said. He’d been looking at the tower one way, ignoring the implications of another point of view. As he realized his mistake, his eyes widened, and yet when he spoke his voice carried a steel edge. “C.W., secure yourself to something. Grab on to the tower. Jim, can you hear me up there?”
“I’m here, Mercer, what’s going on?”
“We’re sitting on top of a methane hydrate deposit. That’s what sank the
“What are you talking about?”
“Methane hydrate. The last great source of fossil fuel on the planet. It’s a gas kept locked in ice by the temperature and pressure on the seafloor. It’s normally stable, but I think this tower’s designed to cause the hydrates to melt. The gas is about one hundred fifty times the volume of its solid state. If the deposit is big enough, that much methane is going to cause the ocean to bubble up like champagne. If it’s bad enough, it will reduce the water density and the
“Is it erupting now?” McKenzie asked, understanding the danger.
“It’s going to.” Mercer’s first assumption about the tower being a heat pump had been correct. Only now he realized it wasn’t forcing cold brine into the soil to keep the hydrate stable, it was designed to draw it up in order to dissipate the chill in the warmer shallower water and trigger a gas burst.
The
And the fire reported just before she sank? Methane hydrate, even in its ice form, was extremely flammable. The air around the ship would have been saturated with gas, and even the smallest spark would have set off a catastrophic explosion. Mercer purged the horrifying image from his mind, that of a vessel engulfed in flames while her crew vainly tried to understand why the small amount of damage from the impact was causing their ship to sink. He refocused his mind on his own impending predicament.
Over the comm link, Mercer could hear hurried orders being shouted in the topside control van. “We have to haul C.W. back aboard,” McKenzie protested.
“I don’t think you have time.”
Mercer pointed to where he wanted Jervis to guide the sub, away from where he suspected the next gas eruption would take place. On a CRT screen, the bottom-profiling sonar had drawn a digital picture of the surrounding seafloor, and it looked as though the tower had been erected in the middle of a series of hills. One of the hills had already vanished in a gas explosion, leaving the deep crater in its wake.
“C.W., what’s your status?” McKenzie asked.