I'm sure we both mean the same thing. pH ranges from 0 to 14, with 7 being neutral. pHs less than 7 are acidic while pHs greater than 7 are alkaline (basic). So seawater is basic and could never, given the chemistry of eroding rocks and existing reefs, become acidic. You say it is becoming acidic - the data may suggest it could become less alkaline, I don't know.
Back in the 1980s I could get worms by sticking a tent peg into the lawn and connecting the active off the extension cord. All the worms would come to the surface. Then a couple of people died doing it and I stopped. Now you can't do it, it would just trip out.
The shares are sold and traded on an open market to raise capital to build things. Anyone is allowed to buy them. If Australians want to own their own mining companies it is easy, just buy the shares.