Otiluke's freezing sphere states:
A frigid globe of cold energy streaks from your fingertips to a point of your choice within range, where it explodes in a 60-foot-radius sphere. Each creature within the area must make a Constitution saving throw. On a failed save, a creature takes 10d6 cold damage. On a successful save, it takes half as much damage.
If the globe strikes a body of water or a liquid that is principally water (not including water-based creatures), it freezes the liquid to a depth of 6 inches over an area 30 feet square. This ice lasts for 1 minute. Creatures that were swimming on the surface of frozen water are trapped in the ice. A trapped creature can use an action to make a Strength check against your spell save DC to break free.
You can refrain from firing the globe after completing the spell, if you wish. A small globe about the size of a sling stone, cool to the touch, appears in your hand. At any time, you or a creature you give the globe to can throw the globe (to a range of 40 feet) or hurl it with a sling (to the sling’s normal range). It shatters on impact, with the same effect as the normal casting of the spell. You can also set the globe down without shattering it. After 1 minute, if the globe hasn’t already shattered, it explodes.
Assume that I am deep underwater with the surface nowhere in sight, and that I have the means to cast spells underwater. I cast Otiluke's freezing sphere, targeting a point 120 feet away from me (which is also underwater). What happens? Does the spell reach the intended target? Does it explode as soon as it leaves my hand and touches the water? Does any water get frozen?
Additionally, does anything different happen if I use the option to refrain from firing the globe and instead throw it or launch it with a sling?