Roko's Catalyst by Michael Blackbourn

SPSFC

The AI-ravaged world humanity once knew has vanished under a treacherous sea. A small fleet of ships survives, trapped for thirty years in constant cycles of freezing and thawing. The ships endure, suspended in ice above a seemingly bottomless chasm. The next thaw threatens to be the final one and would put an end to the survival of the fleet. Hendry has only known this brutal freezing cycle in his thirteen years of life. Like the other survivors, he scavenges on the ice by dogsled and races back to his ship before the icy crust melts. Knowing that it’s only a matter of time until a big enough thaw destroys the fleet, he befriends an unlikely pair of survivors: one an old mercenary, the other a mysterious young girl. She has an ability to predict the thaws, and may have discovered the secret to escaping the knife's edge humanity inhabits. But someone or something wants to stop them all. Now Hendry and his companions are on a mission, and time is running out. The ice will thaw.