To the roots of the mountains I sank down;
the earth beneath barred me in forever.
But you brought my life up from the pit,
O LORD my God.
You have to wonder how deep Jonah sank. In the last verse he was talking about seaweed, and in this verse he is talking about being down with the roots of the mountains. Regardless, it was God who brought Jonah up.
In this verse Jonah acknowledges that God was the one who brought him back up. He was not out of God's reach. Even though Jonah was trying to run from God, it was God who brought him back.