(thread updated as I find them)
First was Wyllie Lionel Wyllie’s “Davy Jones’s Locker” (1890) https://collections.rmg.co.uk/collections/objects/561491.html
Edward Moran, “The Valley of the Sea” (1862) http://collection.imamuseum.org/artwork/56245/
Eugen von Ransonnet-Villez, “Painting made from a drawing performed in an underwater submersible” (ca. 1867) https://publicdomainreview.org/collection/underwater-landscapes-of-eugen-von-ransonnet-villez (Naturhistorisches Museum Wien)
Alexis Rockman, “Great Lakes Cycle” http://alexisrockman.net/great-lakes/ (Grand Rapids Art Museum)
Premodern depictions welcome as well—Alexander the Great in the glass barrel, Berliner Alexanderroman (ca. 1320)
David C. Gallup, kelp forest (?) http://www.dgallup.com (many other works)
Douglas Henderson, multiple works https://douglashendersonehi.com/Image.asp?ImageID=1824349&apid=1&gpid=1&ipid=1&AKey=4YBGL8XG