Coy orphan, age uncertain, a subject for deep study (12)

I believe the answer is:

oceanography

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'study' is the definition.
(oceanography is a kind of study)

'coy orphan age uncertain' is the wordplay.
'uncertain' indicates anagramming the letters.
'coy'+'orphan'+'age'='coyorphanage'
'coyorphanage' is an anagram of 'OCEANOGRAPHY'.

'a subject for deep' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.

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(Other definitions for oceanography that I've seen before include "Scientific study of the seas" , "Study of the sea" .)

I've seen this clue in The Guardian.

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