Mariner down below found tiny white crystals there (10)

I believe the answer is:

saltcellar

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'tiny white crystals there' is the definition.
I can't judge whether this definition defines the answer.

'mariner down below' is the wordplay.
'mariner' becomes 'salt' (synonyms).
'down below' becomes 'cellar' (I can't explain this - if you can you should believe this answer much more).
'salt'+'cellar'='SALTCELLAR'

'found' is the link.

Can you help me to learn more?

(Other definitions for saltcellar that I've seen before include "Small table dish" , "Condiment shaker" , "Diner's sprinkler" .)

I've seen this clue in The Irish Times.

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