The dictionary definition of hydrosphere answers this question.
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What is the difference between hydrosphere and oceans?
which is more comprehensive?
I'd say one big difference is that "ocean" is a word that people are familiar with. I think "hydrosphere" is the official term for rabies.
Actually, the dictionary does not differentiate between the two terms. It just states that hydrosphere is the watery part of the earth including oceans, lakes, etc.
Can we say hydrosphere is more general than ocean ?
I feel a crossword clue coming on now I've had the pun pointed out!
As a translator, I think dictionaries not always provide the accurate meaning. Thus, I find it useful to ask native speakers.
Thank you all for your comments.