Air bubble

We shot into the depths - three metres, six metres. | knew | had to be careful because | could withstand a lot more pressure than Annabeth. She fought and struggled for breath as bubbles rose around us.
Bubbles.
| was desperate. | had to keep Annabeth alive. | imagined all the bubbles in the sea - always churning, rising. | imagined them coming together, being pulled towards me.
The sea obeyed. There was a flurry of white, a tickling sensation all around me, and when my vision cleared, Annabeth and | had a huge bubble of air around us. Only our legs stuck into the water.
She gasped and coughed. Her whole body shuddered, but when she looked at me, | Knew the spell had been broken.

SoM ch.13