Write off wreckage in Timor Sea (8)

I believe the answer is:

amortise

I'm a little stuck... Click here to teach me more about this clue!

'write off' is the definition.
(I've seen this before)

'wreckage in timor sea' is the wordplay.
'timor sea' can be anagrammed to 'AMORTISE'.
But, I am not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for amortise that I've seen before include "Gradually write off initial costs" , "Liquidate gradually" .)

I've seen this clue in The Independent.

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