Is "an ocean of flowers" singular or plural?
Solution 1:
It's an interesting construction to be sure. If it had been a lot of, you would not be bothered by a plural verb.
- A lot of flowers are in bloom right now.
- There are a lot of flowers in bloom right now.
The author seem to be construing an ocean of to be a quantifier that works the same way as a lot of works. That is, it does not change the number any more than words like some or many do.