The Dive

The research station sat on a small rocky platform above the water, three hours by boat from the nearest coast, surrounded by the kind of deep blue ocean that made you feel very small and very aware of how much was underneath you.

Mara was twelve and her brother Sol was ten and they had been coming here every summer since they were small because their mother ran the station. Dr. Adisa studied deep sea geology, which meant she spent a great deal of time looking at rocks that were very far underwater, which Mara had always thought was one of the more interesting jobs a person could have.

The station had three research submarines, each one painted bright yellow so they were easy to spot in the water. The largest one, which the scientists called Big Lemon, was used for serious research dives. The smallest one, which everyone called the Pip, was used for shallow water surveys and also, unofficially, for taking Mara and Sol down to look at things when their mother had time and the sea was calm.

Mara loved the station in the way you love places that have been part of your life for as long as you can remember. She loved the smell of salt and machinery and the particular sound the water made against the platform legs at night. She loved the way the scientists talked at dinner, always about their work, always as if the most interesting thing in the world was whatever they happened to be studying.

It was the Pip that Sol was looking at on the morning everything changed, hanging over the side of the platform railing with his binoculars, which he carried everywhere the same way Mara carried her dive tablet everywhere, as a natural extension of himself.

"There is something wrong with the seafloor," he said.

Mara came and stood beside him. "What do you mean wrong?"

"There is a section about four hundred metres out," Sol said, handing her the binoculars. "Where the colour is different. Look at the water there. It is a different shade."

Mara looked. He was right. Most of the water around the station was the same deep blue. But in the area Sol was pointing at, maybe four hundred metres to the north, the water had a faint greenish tint that was different enough to notice if you were paying attention, which Sol almost always was.

"Could be a thermal vent," Mara said. "Or a bloom of something. Algae maybe."

"Mum's sensors would have picked up a thermal vent," Sol said. "And it is not the right shape for algae. Look at the edges. They are too straight."

Mara looked again. He was right about the edges. The green patch was not the irregular, spreading shape of a biological bloom. Its boundaries were almost geometric, roughly rectangular, much more regular than anything natural tended to be.

"We should tell Mum," Mara said.

"She is in a satellite call until noon," Sol said. "She said not to disturb her unless something was on fire."

"This is not on fire," Mara said.

"No," Sol agreed. He looked at her sideways. "The Pip is fuelled. The sea is very calm. We are both certified for shallow water surveys down to thirty metres."

"The green patch might be deeper than thirty metres," Mara said.

"The water over it looks shallower than the water around it," Sol said. "See how the colour lightens slightly right at the centre? That means the bottom is closer to the surface there. Raised seafloor."

Mara looked. He was right again. She found this both impressive and slightly annoying.

"We stay within sight of the station," she said. "We do not go below thirty metres. We log the dive properly before we go. And we leave a note for Mum."

"Obviously," Sol said. He was already moving toward the Pip.