Why in the News?
A new study from the University of Plymouth has revealed that over 21% of the global ocean has significantly darkened in the last two decades.
What is Ocean Darkening?
- Ocean darkening refers to the reduction in sunlight penetration into the ocean’s upper layers, known as the photic zone (up to 200 meters deep), where sunlight drives photosynthesis and supports marine biodiversity.
- This process is measured using the diffuse attenuation coefficient (Kd 490), which tracks how quickly light diminishes as it passes through seawater.
- The photic zone is essential for phytoplankton productivity, oxygen generation, marine food chains, and the regulation of global climate.
Recent Report Citing Ocean Darkening:
- A new study by researchers from the University of Plymouth, published in 2024, titled “Darkening of the Global Ocean”, revealed that 21% of the global ocean has significantly darkened from 2003 to 2022.
- Key findings:
- 9% of the ocean saw a drop of more than 50 meters in light penetration—equal to the area of Africa.
- 2.6% experienced a loss exceeding 100 meters in photic depth.
- Affected Region: The study found the Arctic, Antarctic, Gulf Stream, and North Sea among the worst affected regions.
- Causes:
- Algal blooms from nutrient runoff in coastal areas.
- Warming seas, altered plankton dynamics, and changing ocean currents in open ocean zones.
Implications of Ocean Darkening:
- Ecosystem Disruption: Light-dependent species, such as Calanus copepods, are being pushed into shallower zones, increasing predation and competition.
- Loss of Habitat: The shrinkage of the photic zone could be one of the largest marine habitat losses ever, affecting fish stocks and biodiversity.
- Climate Feedback Loop: Reduced photosynthesis in oceans could weaken the ocean’s role in carbon sequestration and oxygen production, worsening climate change.
- Threat to Global Fisheries: The contraction of productive zones affects fish populations, jeopardising fisheries and food security.
- Scientific Concern: Researchers warn that this hidden crisis could fundamentally alter marine ecosystems if not urgently addressed.
| [UPSC 2025] With reference to the planet Earth, consider the following statements:
I. Rain forests produce more oxygen than that produced by oceans. II. Marine phytoplankton and photosynthetic bacteria produce about 50% of the world’s oxygen. III. Well-oxygenated surface water contains several folds higher oxygen than that in atmospheric air. Which of the statements given above is/are correct? Options: (a) I and II (b) II only * (c) I and III (d) None of the above statements is correct |
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