雅思阅读 75: When the Ocean Runs Out of Breath（当海洋停止呼吸）

改编自 ScienceDaily / University of California San Diego（2026年7月）。雅思阅读 Section 3 难度，约 1050 词。 素材来源：https://www.sciencedaily.com/releases/2026/07/260719035939.htm

Reading Passage

A. The world's rivers, lakes, coasts and open ocean are quietly losing oxygen, and researchers warn the consequences could reshape life on Earth. In a review published in 2026, scientists led by the Scripps Institution of Oceanography described how dissolved oxygen is vanishing from aquatic systems at an accelerating rate, potentially pushing the planet into what they call an "unsafe space". What makes the trend alarming is its momentum. Some of the resulting changes may persist for centuries and might not be reversible within a single human lifetime; once a body of water has been depleted of oxygen, simply cooling it back down does not guarantee that the original community of fish and invertebrates will return. The decline is not confined to one region or one kind of water body. It touches the deep ocean, coastal estuaries, rivers and lakes alike, linking a problem that was once studied as a series of local complaints into a single, planet-wide symptom. The review's authors argue that oxygen loss is not an isolated nuisance but one strand of a tangled web of environmental stresses — warming, pollution, biodiversity collapse and acidification — that reinforce one another rather than acting independently.

B. To frame the threat, the team turned to the Planetary Boundaries framework, introduced in 2009 to identify the processes that keep the planet stable. That framework tracks nine such processes — climate change, ocean acidification, biodiversity loss, aerosol loading, ozone depletion, freshwater change, land-use change, chemical pollution and biogeochemical flows — and warns when human activity pushes any of them beyond a safe limit. The researchers propose that dissolved oxygen should be formally added as a tenth boundary. Their reasoning is straightforward: the health of the planet depends on aquatic ecosystems functioning normally, and those ecosystems require oxygen. Lead author Erica Ferrer and senior author Lisa Levin developed the idea after attending a 2019 UN climate conference held in Madrid, where they noticed that oxygen loss was repeatedly mentioned but never treated as a boundary in its own right. Placing it on the map, they argue, would force policymakers to consider oxygen loss alongside climate and biodiversity rather than as a footnote in a larger report. The framework already warns when any boundary is breached; adding oxygen would mean that measurable declines in dissolved water could trigger the same kind of international alarm that has surrounded carbon emissions and the destruction of tropical forests. Critics, however, caution that the nine existing boundaries were themselves chosen partly for tractability, and that bolting on a tenth may dilute attention rather than sharpen it.

C. Three forces drive the decline, and they work together. The first is warming. Warm water simply holds less dissolved oxygen — the same physical principle that makes a warm glass of fizz go flat faster. As the surface ocean heats up, its capacity to absorb oxygen from the air falls. The second is stratification. A layer of warm, light water now floats on colder, denser water below, acting like a lid that prevents oxygen-rich surface water from mixing down into the depths. Ventilation of the ocean interior slows, and deep waters that were once replenished grow steadily more starved of oxygen. The third is nutrient pollution. Fertiliser runoff and sewage trigger explosive growth of algae; when the algae die and decompose, bacteria consume oxygen faster than it can be replaced. Since 1960, the world's oceans have lost roughly two per cent of their total oxygen — about double the amount that climate models had predicted, a gap that suggests scientists still underestimate how quickly the system is responding to the warming it has already absorbed.

D. The biological consequences ripple upward from microbes to top predators. In coastal areas, nutrient-driven depletion produces "dead zones": stretches of sea so low in oxygen that fish and crabs either suffocate or flee, abandoning fishing grounds that communities depend on. The Gulf of Mexico, the Baltic and Black Seas, the Bay of Bengal and the coasts off Oregon and Peru have all seen such zones multiply in recent decades. In the open ocean, naturally occurring low-oxygen layers known as oxygen minimum zones are spreading and creeping upward toward the surface, squeezing mobile species into thinner and thinner bands of habitable water. Even marine mammals, which breathe air at the surface, suffer: oxygen loss reduces or displaces the prey they hunt and damages the seafloor habitats on which food webs rest. Commercial fisheries, already squeezed by overfishing and warming, face a further, largely invisible erosion of the water's capacity to sustain the stocks that millions of people rely on for protein and income.

E. Perhaps most worrying is the way oxygen loss feeds back into climate change itself. As oxygen falls, the chemistry of the water shifts. Microbes that thrive without oxygen release nitrous oxide, a potent greenhouse gas, and altered microbial cycling can weaken the ocean's ability to absorb carbon dioxide. In other words, a warming world robs the ocean of oxygen, and a starved ocean may then accelerate the very warming that began the process. The review's authors hope their work will encourage researchers and governments to treat deoxygenation as one part of a single interconnected crisis rather than a separate problem to be solved in isolation. The remedies are well understood even if they are politically difficult: cut greenhouse-gas emissions, slow the warming that drives solubility and stratification, and curb the nutrient runoff that creates coastal dead zones. Whether the world moves fast enough may determine whether the century ahead sees aquatic oxygen recover — or settle into a new, poorer equilibrium that no living ecosystem was designed to endure. The review's authors are careful to add that deoxygenation is reversible in principle, unlike some other planetary damages: cool the water, cut the fertilisers running off the land, and oxygen levels can climb back. The question is whether societies will act quickly enough to keep that option open before the most vulnerable ecosystems, and the fisheries and coastlines that depend on them, cross their own points of no return.

Questions 1-4

Choose the correct heading for paragraphs B, C, D and E from the list of headings below.

List of Headings i. A global picture of disappearing oxygen ii. Why oxygen should join the planetary boundaries list iii. Three forces that drain the water iv. How the loss reaches fish, fisheries and marine mammals v. A self-reinforcing cycle and its remedies vi. The history of commercial fishing regulation vii. Why oxygen is toxic to most ocean microbes

1. Paragraph B: ____
2. Paragraph C: ____
3. Paragraph D: ____
4. Paragraph E: ____

Questions 5-8

Choose the correct letter, A, B, C or D.

5. According to the review, why might oxygen loss be especially serious? A. It is confined to a small number of tropical rivers. B. Some changes may persist for centuries and not reverse in a human lifetime. C. It has already begun to reverse on its own. D. It affects only the open ocean, not coasts.

6. Why do Ferrer and Levin want oxygen added to the planetary boundaries? A. To remove climate change from the existing list B. To force policymakers to treat it as a major interconnected threat C. To show that the framework is scientifically invalid D. To raise funding for underwater research vessels

7. What is the main effect of stratification on ocean oxygen? A. It mixes surface and deep water much more vigorously. B. A warm surface layer prevents oxygen from reaching deeper water. C. It raises oxygen levels in the deepest waters. D. It has no measurable effect on oxygen distribution.

8. Why are rising oxygen minimum zones particularly worrying for fish? A. They squeeze habitable water into thinner bands as the zones creep up. B. They make deep water warmer and more comfortable for fish. C. They always increase the size of fish stocks. D. They attract sharks away from fishing grounds.

Questions 9-13

Do the following statements agree with the claims of the writer?

Write:

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

9. The world's oceans have lost roughly two per cent of their oxygen since 1960.
10. Warm water holds more dissolved oxygen than cold water.
11. The Gulf of Mexico is one region where dead zones have multiplied.
12. Marine mammals are unaffected by oxygen loss because they breathe air.
13. The 2026 review was published in a journal based in Japan.

Questions 14-15

Complete the summary below using NO MORE THAN TWO WORDS from the passage.

Nutrient runoff triggers algal blooms; as the algae die and (14) __________, bacteria consume oxygen faster than it is replaced, producing coastal (15) __________.

答案与解析

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