"great ocean" is correct and usable in written English.
You can use it to describe a large ocean. For example, "From her bedroom window, she could see the great ocean stretching out to the horizon."
"Oh, great ocean," Bono sang.
He sees space as a great ocean.
HOBOKEN HISTORICAL MUSEUM "Destination Hoboken: The Great Ocean Liners of Hamburg-American and North German Lloyd".
The Independence represents one of the last great ocean liners still in commercial service.
We don't know the exact threshold at which sinking, and the great ocean conveyor, could stop.
Even the recently built opera house evokes a great ocean-going liner.
You can get there via the various towns along Rt 127, a great ocean-side drive.
Both are part of the so-called Great Ocean Conveyor Belt of ocean circulation.
I was no exception and grew up in Geelong, which is near the Great Ocean Road and other great beaches.
Think of the world's great road trips – the Amalfi Coast, the corniche of the Côte d'Azur, the Great Ocean Road, the Pacific Coast Highway, Route 66..
