Related to heat that's somewhat tropical - or Icelandic? (7)

I believe the answer is:

caloric

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'related to heat' is the definition.
I can't judge whether this defines the answer.

'somewhat tropical or icelandic?' is the wordplay.
'somewhat' indicates the answer is hidden within the clue.
'CALORIC' is hidden within 'tropical or icelandic'.

'that's' acts as a link.

Can you help me to learn more?

(Another definition for caloric that I've seen is " Thermal".)

I've seen this clue in The Independent.

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