Pitt halted their descent as the sea bottom came into view. Giordino let out a low whistle. “Looks like somebody was building a freeway down here.”
They had dropped onto one of the shadowy linear images they’d seen on the sonar. In person, the lines were much more defined and clearly not a natural geographic feature. They could only be mechanically made tracks.
Pitt guided the submersible to a wide set of parallel marks and hovered over them. “Someone’s been down here with some heavy equipment, all right.”
“The indentations are over ten feet across,” Giordino said. “I don’t know of many vehicles large enough to make that kind of a track.”
Pitt shook his head. “It’s not from an oil or gas well operation. Somebody was conducting a large-scale mining operation.”
“You think someone was down here scooping up manganese nodules?”
“A good bet. Probably high in gold content.”
Pitt thrust the submersible across the scarred seabed, where two different track marks crisscrossed a wide area. “Do those second tracks look familiar?”
“Now that you mention it, they look an awful lot like the tracks around the Alta’s diving bell.”
“My thoughts exactly.”
As Pitt circled away from the tracks, he noticed the water depth decrease slightly. The depression they’d seen in the sonar image was evident out the viewport in the form of a bowl-shaped indention that dropped sharply at its center. The tracks were most prevalent around this center point.
“Do you think they blasted here?” Giordino asked.
“Kind of looks that way.”
“Whoa, ease off the gas a second. The water temperature just spiked about fifty degrees.”
Pitt eased off the thrusters, nudging the submersible toward the center of the depression.
“Temperature’s still rising,” Giordino said. “Up to one hundred and forty degrees, one-fifty, one-sixty . . . now dropping.” He tracked it for another minute. “It peaked at about one hundred and sixty-five degrees.”
“It’s a thermal vent,” Pitt said, “right in the heart of their mining grid.”
“Makes sense. Deepwater vents are known for their rich surrounding minerals.”
“I bet this one comes with a high dose of mercury.”
“That must be the source,” Giordino said. “Odd that we’ve never run across high levels of mercury in other hydrothermal vents we’ve examined.”
“Might have something to do with the explosives. There could be a pent-up base of mercury beneath the vents that’s dispersed by a blast.”
“Makes sense. If it’s a natural deposit that was disturbed, that would explain why we didn’t find any overt evidence at the other two sites.”
“If we look closer,” Pitt said, “I bet we’ll find the same telltale tracks and man-made depressions.”
?
?Now we know what to look for. Let’s get back to the ship. I’d like another look at the last two sites’ sonar records.”
“Sure,” Pitt said, “but first one quick detour.”
Circling the depression, he scanned the depths before goosing the submersible toward a slender brown object jutting from the sand. Hovering above it, they could see it was neither a ship nor a sailboat. It was a large log.
“So much for my sunken boat,” Giordino said. “It’s just a big log that rolled off a cargo ship.”
“Not so fast,” Pitt said. He circled to the other side, where they could see it was actually a dugout canoe.
“Will you look at the size of that?” Giordino said as he reached up and activated an external video camera. “It must be over thirty feet long.”