I'm in the US Coast Guard. I haven't been in long (4ish years), but I spent a few years off the west coast of Panama, in deep waters, while looking for drug runners. Some weird/cool stuff I've seen:
Summer lightning, more than 1 flash per second, for hours at a time. Cool as hell during night watches, but it's unnerving to see sparks jump between antennas only a few feet from you. The tips of metal parts (masts, anntenas, etc) glow spookily during lightning storms. I learned later it's called St. Elmo's Fire.
I always liked bioluminescence. The first time I went down there, I started seeing rapid streaks of blue-green glow under the water. After a few hours of watching it, I figured out it was dolphins, either hunting or following our swell. They looked like alien rockets, and weirded me right out, until I figured it out. The dolphins stir up the microscopic glowing life whenever they moved. Must've made it hard for them to sneak up on prey.
During certain algae blooms (red during the day), they glow from the bioluminescence was bright enough that it cast my shadow on the bulkhead behind me. Very cool.
On boring/still nights, I would try to stargaze on the big eyes (giant mounted binoculars). I showed got to show some of the younger watchstanders what the moon looks like up close, the moon's of Jupiter, and the rings of Saturn. Couldn't see any detail, just vague shapes.
I saw the giant mess that's off the west coast of Panama. Unbelievable amounts of trash, presumably from the ships going through the canal. Soooo. Much plastic. A lot of shoes, for some reason.
Sailing through gigantic pods of dolphin. I hesitate to use the word pod, because it doesn't sound large enough. Herd, maybe? Hundreds of dolphin, in every direction. They looked like they had someplace to be...do dolphin have conventions?
I have other stories, but they aren't as weird or strange as these.