As warming continues, scientists warn the oxygen content of oceans across the planet could be more and more reduced, with serious consequences for the future of fish and other sea life.

【小题1】. One is the simple fact that as water gets warmer, it can hold less dissolved(溶解的)oxygen. The other reason is less obvious.【小题2】—either from the atmosphere, or from photosynthesizing algae floating at the top of the sea. The oxygen then spreads to the deep ocean as the surface water slowly sinks.

Global warming is expected to reduce the mixing of the ocean by making surface seawater lighter. That's because in a warmer world we can expect more rainfall and more melting of glaciers, icebergs, and ice sheets.【小题3】.The extra heat from the warming atmosphere will also make surface water expand and thus make it lighter still.【小题4】. Instead, more of the oxygen will remain near the surface, where it will be used up by oxygen-breathing organisms.

A low-oxygen ocean may become an inescapable feature of our planet. A team of Danish researchers wondered how long oxygen levels would drop if we could somehow reduce our carbon dioxide emissions to zero by 2100. They determined that over the next few thousand years oxygen levels would continue to fall, until they declined by 30 percent. The oxygen would slowly return to the oceans, but even 100,000 years from now they will not have fully recovered.【小题5】