Note: Since deep-sea mining is mentioned in this article I thought of adding a few of links in an effort to sum up how vast and serious the problem is.
These polymetallic nodules that mining companies want to extract from the deep sea, well it looks like they produce oxygen through electrolysis [source]. Meaning, without this source of oxygen these deep-sea ecosystems are going to literally suffocate.
66% of the entire planet is deep ocean (≥200 m). Data show that humans have visually observed less than 0.001%, a total area approximately a tenth of the size of Belgium [source]. So companies want to move in and exploit the seabed for profit, one them is the notorious TCM / The Metals Company, while marine scientists say that we need to know what the impact is first, before making any move.