A gas explosion involving Ross Sea (8)

I believe the answer is:

sargasso

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

I don't understand how the rest of the clue works.

(Other definitions for sargasso that I've seen before include "Sea in the North Atlantic with no land borders" , "Gas soars around the North Atlantic sea" , "Sea noted for seaweed and eels" , "Mass of weed" , "Atlantic sea surrounded by ocean currents" .)

I've seen this clue in The Guardian.

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