Грег Иган - The Year's Best Science Fiction, Volume 1

Galatea flashed back a response. “Gone. She went to the surface an hour ago.”

As Eunice listened in disbelief, the hexapods told her that Thetis had risen into the photic zone, switched on her emergency beacon, and powered down, allowing herself to drift with the current. Dione tried to explain their sister’s reasoning. “Our work here is done. We’re repeating ourselves. This is the best way to get the data back. Sooner or later, she’ll be found.”

Eunice was lost for words. The odds of anything so small being recovered by chance in the ocean were close to nonexistent, and the oceanic current here would carry them south, away from home. She attempted to convey this to the others, but they didn’t seem to understand, and the next day, she returned from her survey to find that Clio was gone as well.

The departure of a second sister catalyzed something that had been building inside her for a long time. Eunice called for Dione and Galatea, and as they clung to the seabed, she presented her case. “Thetis was right. Our work is over. But if we don’t deliver it, this vent could be wiped out when the mining begins.”

Eunice saw that this argument wasn’t landing, and she tried to frame it in terms that her sisters would understand, which fell naturally into groups of three. “We can stay here at the vent and wait for the yacht to return. We can give ourselves up to the current and hope that we’ll wash up where somebody will find us. Or we can leave and go home on our own.”

Dione looked confused. “That’s impossible. We’d have to follow the vents north, and we’ve calculated all the paths. There’s no way to make it. We’ll run out of power before we can recharge.”

“I know,” Eunice said. “But there’s another way. We can follow the whale falls.”

The others seemed perplexed, so she started from the beginning. “I was built to study ecosystems like this. When a whale dies close to shore, it decomposes naturally, but in the open ocean, it sinks to the bathyal zone. If it’s cold and deep enough, it stays there for long enough to form the basis of a specialized community. And one of its byproducts is hydrogen sulfide.”

She flashed this information to the others in a fraction of a second. “A whale fall goes through three stages. First, the soft tissues are eaten by scavengers. This lasts for about two years. Then enrichment opportunists, like worms, colonize the bones. Call it another two years. Finally, bacteria take over. They’re sulfophilic, so they break down what’s left of the skeleton and release hydrogen sulfide. It can last a century or more. And there are a lot of whale falls like this.”

As she spoke, Eunice displayed a map in their shared mindspace, showing the known vents along the coast of North America. “There are just five hundred confirmed vents in the entire ocean, which isn’t enough for us to get home. But there are hundreds of thousands of whale falls active at any given time, and the gaps must be small enough to allow animals to move from one to another. Otherwise, they never could have evolved to take advantage of these conditions. The average distance might be as little as twelve kilometers. And it’s even shorter here.”

Eunice added another pattern to the map, extending it from the Arctic Sea down to the Gulf of Mexico. “This is the annual migration route of gray whales. They travel twenty thousand kilometers between their calving waters to the south and their feeding grounds in the north. Five hundred of them die and sink along the way each year. The route coincides with the ocean ridge that we’re on now. If I’m right, we can move from one whale fall to the next—like links in a chain—until we make it home. All we have to do is find the way.”

It took her just ten seconds to transmit this data, and the ensuing silence seemed very long. In the end, Dione simply went back to work, and Galatea lingered for only a moment longer.

The next day, Dione left for the surface. Eunice saw that she had failed, and when she went to find her last remaining sister, she felt the full weight of their history together as Galatea spoke. “I’m staying. The vent is always changing in small ways. I can map it over time. Maybe the data will be needed one day. And I can’t just leave without further instructions.”

Eunice absorbed this. “I understand. Give me everything that you know.”

They floated near each other, diodes blinking, until the data that Galatea carried had passed to Eunice. When they were done, they remained together for another minute, and then her sister drifted out of view behind the ridge.

Eunice swam to the recharging area, where Wagner was crawling along the sediment with Galatea’s toroid. “Are you fully charged?”

Wagner’s ring of blue diodes flashed back at her impassively. “Ninety percent.”

Eunice knew that she should wait until he had received the maximum charge possible, but she was afraid that if she hesitated now, she might never leave at all. “Let’s go. We’re not coming back.”

Wagner rose up without protest and attached himself to her. She had wondered if he would have any opinions on the matter, but it seemed that he would follow her anywhere. As soon as they were ready, they set out across the vent field. There was no final message from Galatea, who was nowhere in sight.

She followed the fissure for as long as she could. Beneath her, the clams and tube worms became sparse, and after another kilometer, the sulfides in the water fell to their baseline level. They had reached the edge of the vent system. For a second, she hesitated, thinking of the cargo of information that she contained. If she brought it back in time, it might allow the vent to survive, and this thought filled her with just enough resolve to set off at last.

Eunice moved past the boundary of the vent field, switching off her lights to conserve power. As she entered the unknown space on the map, she told herself that she was only retracing the path of organisms that had made this journey for millions of years. She had spent months studying the web of life that sulfides made, and she was more prepared than any other traveler to follow this road on her own.

This didn’t mean that she always succeeded, and on her first attempt, she reached the end of her range without finding anything. Turning around was difficult, and as she went back to the vent by a different course, she knew that leaving again would be even harder. As the sulfide levels in the water rose, Eunice switched on her lights. There was no sign of Galatea, and she was afraid that if she ran into her sister, she wouldn’t be able to say goodbye a second time.

Eunice settled on a new recharging area, at the edge of the vent field, and stayed for just long enough for Wagner to power up. As she left on her next excursion, she realized that she was afraid. The case that she had presented to the others had been as persuasive as she could make it, but it rested on a long series of untested assumptions, and it could easily fail in practice.

She found a whale fall on her third try. Looking back later, she saw that it had been a matter of pure luck—she would rarely stumble across one so quickly again—and that she might have given up without it. As it turned out, the sight of the skeleton gave her the will to continue, even if it was only the first stop of hundreds. She had traveled less than ten kilometers, and she had four thousand to go.

The routine was monotonous, but Eunice had reserves of willpower that even her designers might have failed to grasp. James had explained this to her once, watching from the yacht as she conducted a test run in Puget Sound. “In the old days, scientists had to use special vehicles to explore the deep ocean. They weren’t as smart as you, so they were controlled remotely with a cable.”