Q4.
The CO2 dissolved in the ocean is disturbed when the global temperature increases. What will happen to marine life?
Answer
Marine life is hit from two directions at once — the sea becomes more acidic, which attacks shells and coral, and the warmer water holds less dissolved oxygen and less dissolved CO2, which stresses fish and weakens the ocean as a carbon sink.
Higher global temperature
(a) More CO2 in the air → more dissolves → carbonic acid → ocean acidification
→ carbonate shells of plankton, molluscs and corals dissolve / form poorly
(b) Warmer water dissolves less gas → less dissolved O2 → fish struggle to respire
(c) Warmer water absorbs less CO2 → weaker carbon sink → still more CO2 left in the air
(a) More CO2 in the air → more dissolves → carbonic acid → ocean acidification
→ carbonate shells of plankton, molluscs and corals dissolve / form poorly
(b) Warmer water dissolves less gas → less dissolved O2 → fish struggle to respire
(c) Warmer water absorbs less CO2 → weaker carbon sink → still more CO2 left in the air
Why gases behave this way: the solubility of a gas in water falls as the water gets warmer — the same reason a warm fizzy drink goes flat faster than a cold one. So warming does two contradictory-sounding things: the atmosphere pushes more CO2 in because there is far more of it up there, yet each litre of warm sea water can hold less gas of any kind, including the oxygen fish need. The chapter states both halves: excess CO2 "increases ocean absorption, making sea water more acidic", and "warmer ocean water reduces the ocean's capacity to absorb CO2 as an effective carbon sink."
| Group of organisms | What happens to them |
|---|---|
| Phytoplankton | Base of every marine food chain and a huge source of oxygen — damage here starves everything above it |
| Shell-forming organisms (molluscs, some plankton) | Acidic water makes calcium carbonate shells thinner and harder to build |
| Coral reefs | Bleach in warm water and dissolve in acidic water; reef fish lose their habitat |
| Fish and coastal fisheries | Less dissolved oxygen, less food, shifting migration routes — catches fall |
Scale check: the chapter's Threads of Curiosity box tells you why this reservoir matters so much — "out of the total quantity of global carbon, 71% carbon is found in oceans", while the atmosphere holds only about 1%. Even a small change in the ocean's chemistry therefore moves a very large amount of carbon.