The distribution of subsurface microplastics in the ocean

Area of Science:

• Marine Science
• Environmental Science
• Oceanography

Background:

• Marine plastic pollution is a significant global challenge, with microplastics (1 µm–5 mm) being the most abundant plastic type.
• Current research primarily focuses on surface microplastic concentrations, limiting understanding of their distribution in deeper ocean layers.

Purpose of the Study:

• To synthesize global depth-profile data of microplastics to understand their distribution and transport mechanisms in the oceanic water column.
• To investigate the relationship between microplastic size and depth distribution.
• To assess the contribution of microplastics to particulate organic carbon.

Main Methods:

• Synthesized data from 1,885 stations collected globally between 2014 and 2024.
• Analyzed microplastic abundance and distribution across various ocean depths.
• Compared distribution patterns of small (1 µm–100 µm) and large (100 µm–5,000 µm) microplastics.

Main Results:

• Microplastic abundances range from 10⁻⁴ to 10⁴ particles/m³ across the water column.
• Smaller microplastics exhibit a more even distribution with depth, suggesting longer persistence.
• Larger microplastics concentrate in stratified layers and mid-gyre accumulation zones within the top 100m.
• Microplastics constitute a measurable fraction of particulate organic carbon, increasing with depth from 0.1% at 30m to 5% at 2,000m.

Conclusions:

• Microplastic distribution is size-dependent, with significant subsurface presence.
• Mid-gyre accumulation zones extend into deeper waters, primarily containing larger microplastics.
• Standardization in sampling methods is crucial for accurate assessment of microplastic distribution and oceanic impact.