Why in the News?
A study published in Nature reveals that microplastics have deeply infiltrated the ocean, affecting the planet’s biogeochemical and carbon cycles.
Key Findings of the Study:
- Microplastics (1–100 micrometres) dominate the ocean’s water column, especially below surface layers, unlike larger plastic fragments (100–5,000 micrometres) which remain near the surface.
- Subsurface microplastics were found as deep as 100 metres within ocean gyres—rotating currents that trap and accumulate debris.
- Data was compiled from 1,885 ocean stations (2014–2024), focusing on 50 cm below surface (subsurface layer).
- Over 56 polymer types were detected; buoyant polymers, common in global plastic production, were most prevalent.
- Sources identified:
- Fishing gear, including nylon and polyester nets, was a significant contributor to deep-sea microplastics.
- Plastics sampled often had production dates from the 20th century, highlighting their long degradation timelines.
- Atmospheric deposition contributes 0.013–25 million tonnes annually, with polyester dominant in airborne microplastics.
About Allochthonous Carbon:
- Allochthonous carbon is carbon from external sources introduced into an ecosystem, not produced within it.
- In oceans, plastics are a major source of allochthonous carbon, as they come from land-based human activities.
- Microplastics contribute measurable carbon mass to marine systems, altering natural carbon ratios in ocean layers.
- This distorts the marine carbon pump by affecting the flow and composition of particulate organic carbon (POC).
- Impacts:
- Plastic-derived carbon lacks radiocarbon, which may cause marine POC samples to appear around 420 years older.
- It disrupts microbial activity, nutrient cycling like nitrification and denitrification, and organic matter decomposition.
- Marine microbes ingest plastic-C, affecting food chains and altering biological processes at the base of ecosystems.
| [UPSC 2012] What would happen if phytoplankton of an ocean is completely destroyed for some reason?
Statements: 1. The ocean as a carbon sink would be adversely affected. 2. The food chains in the ocean would be adversely affected. 3. The density of ocean water would drastically decrease. Options: (a) 1 and 2 only* (b) 2 only (c) 3 only (d) 1, 2 and 3 |
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