Many of them are submarine volcanoes, meaning they're underwater, as are 75 percent of the world's volcanoes in total.

它们中大部分都是海下的火山，占世界上火山总数的75%。

Add to that any additional salt and minerals that would be expelled from hydrothermal vents or submarine volcanoes.

再加上从海底的热泉或火山排出的许多额外的盐和矿物。

An undersea or submarine volcano is located below the ocean surface and mostly erupts under water.

海底或海底火山位于海面以下，大部分在水下喷发。

What's most disturbing about this sound is that submarines, volcanoes, and earthquakes have all been ruled out.

这个声音最令人不安的是，潜艇、火山、地震都被排除了。

Many of them are submarine volcanoes meaning their underwater as are 75 percent of the world's volcanoes in total.

其中许多是海底火山，这意味着世界上 75% 的火山都位于水下。

Add to that any additional salt and minerals that would be expelled from hydrothermal vents or submarine volcanoes, and then consider that this whole process has been recurring more or less consistently for 3.8 billion years.

除此之外，还有火山口以及海底火山喷发出的盐和矿物质，这一系列的过程在过去的 38 亿年中反复出现。