What's making duck sounds in the ocean?

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Scientists have been trying to disccover a type of noise that can be heard at the bottom of the ocean since 1960.

At the beginning scientists thought that noise was made by a military object in the depths of the ocean, after a few years of investigation they discovered that the noise appeared each October and disappeared in December, and it can only be heard in the Antarctica.

With that information in their hands they started to realize that the sound was emited by an animal, but they didn't know what animal could make that huge ultra-sound noise that can be heard a few kilometres away.