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The Sylph alternate racial ability goes as so:
Breeze-Kissed: Breezes seem to follow most sylphs wherever they go, but some sylphs are better able to control these winds than others. A Sylph with this racial trait surrounds herself with swirling winds, gaining a +2 racial bonus to AC against non-magical ranged attacks. The Sylph can calm or renew these winds as a swift action. Once per day, the Sylph can channel this wind into a single gust, making a bull rush or trip combat maneuver attempt against one creature within 30 feet. Whether or not the attempt succeeds, the winds are exhausted and no longer provide a bonus to the sylph’s AC for 24 hours. This is a supernatural ability. This racial trait replaces air affinity.
Whilst it says nothing about underwater usage, I would assume this wouldn't work underwater without some kind of infinite air supply with which to draw from?
I don't see such a requirement, and for the most part non-fire spells function the same way underwater. AFAIK it would work fine--the effect generates the gas required to constitute the wind.