Plastic debris accumulates in the ocean because plastic enters marine systems faster than it is removed or broken down. Its persistence, continuing human inputs and transport by ocean currents cause the marine plastic storage to increase over time.
This is core SL and HL content in IB ESS subtopic 4.4, Water pollution. Viewed as a system, the ocean receives plastic through multiple inputs, while its outputs and transformations are comparatively slow.
| Factor | How it causes accumulation |
|---|---|
| Land-based inputs | Mismanaged waste, litter and plastic carried by rivers or stormwater enter the ocean. Synthetic fibres and small plastic particles may also pass through wastewater systems. |
| Marine-based inputs | Fishing gear, ropes, packaging and waste from ships or aquaculture enter the water directly. Lost fishing gear can continue harming organisms through “ghost fishing.” |
| Persistence | Most conventional plastics are non-biodegradable or degrade extremely slowly. Sunlight and wave action fragment larger items into microplastics, but this does not remove the plastic from the system. |
| Ocean circulation | Currents transport debris over long distances. Rotating current systems called gyres concentrate floating material in particular regions. |
| Weak waste management | Limited collection, recycling and regulation allow plastic leakage to continue, especially where consumption rises faster than waste-management infrastructure. |
The Great Pacific Garbage Patch is a named example of debris concentrated by the North Pacific Subtropical Gyre. A common misconception is that it is a solid floating island. It is actually a large region with elevated concentrations of dispersed plastic fragments, fishing gear and microplastics.
Accumulation also has a societal dimension. Coastal and fishing communities may suffer reduced income, damaged equipment and contaminated food resources, although they may have contributed relatively little to the waste. This creates an environmental justice issue.
Exam technique: For an “explain” question, show the causal chain: continued inputs plus slow degradation and limited removal lead to increasing storage. Distinguish fragmentation from decomposition, use systems terminology, and support the explanation with a named example such as the Great Pacific Garbage Patch.