10 across
Purging
most
of
the
Arctic
a
muddle
(9)
Purging most of the Arctic a muddle (9)
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The definition is at the beginning of the clue.
How the clue works
Purging is your definition — something cathartic cleanses or purifies. For the wordplay, take "the Arctic" and lop off the last letter ("most of" does that job), leaving you THEARCTI, then "a muddle" signals an anagram of those letters, which scrambles neatly into your answer.