Following the blowing of the second trumpet something "like [1] a great mountain" that was on fire came crashing down from heaven into the waters of one or more of the earth"s seas. This resulted in a third of the oceans, perhaps a third of the ocean waters, becoming blood. Whether the water became blood, or became a substance like blood, or simply looked like blood, is difficult to determine from the text (cf. Exodus 7:20-21; Psalm 78:43-44; Joel 2:31; Zephaniah 1:3). Literally it could become blood. I understand that the only chemical difference between seawater and blood is that blood contains an iron molecule that is absent in seawater. Perhaps this mountain-like mass (a meteor?) will provide that molecule resulting in a change in the chemical composition of these seas. A third of the creatures living in the sea died, and a third of the ships on the sea perished. Beale took the mountain figuratively to represent a kingdom, specifically the Babylon referred to in chapters11-18. [2][source]
"As of January1 , 1981there were24 ,867 ocean-going merchant ships registered. Imagine the shock waves that would hit the shipping industry if8 ,289 valuable ships were suddenly destroyed! And what about their cargoes!" [3][source]
John was clearly describing supernatural interventions, not natural happenings. [source][source][source]