3.5 Marine Pollution
Human activities introduce a variety of pollutants into the ocean: plastics, oil, heavy metals, nutrients, and chemicals. Understanding their sources, transport, and impacts is crucial for ocean health.
Types of Marine Pollution
Plastics
8+ million tons/year enter ocean. Microplastics in food chain. Gyres accumulate debris.
Oil Spills
Tanker accidents, offshore drilling. Coats wildlife, smothers habitats.
Heavy Metals
Mercury, lead, cadmium. Bioaccumulation in food chain. Industrial sources.
Eutrophication
Excess N & P from agriculture. Algal blooms → dead zones.
Dead Zones
Hypoxic regions where O₂ is too low to support most marine life:
400+
Dead zones worldwide
22,000 km²
Gulf of Mexico (peak)
<2 mg/L
Hypoxia threshold
Plastic Accumulation
Great Pacific Garbage Patch
1.6 million km² of floating plastic. Mostly microplastics <5mm.
Microplastics
Found in deepest ocean trenches, Arctic ice, marine organisms at all levels.
Python: Plastic Distribution
#!/usr/bin/env python3
"""marine_pollution.py - Microplastic distribution model"""
import numpy as np
import matplotlib.pyplot as plt
# Simplified plastic concentration in ocean gyres
# Higher concentration toward gyre centers
def plastic_concentration(r, r_gyre=500, C_center=1e6):
"""
Plastic concentration (particles/km²) vs distance from gyre center
r: distance from center (km)
"""
return C_center * np.exp(-(r / r_gyre)**2)
r = np.linspace(0, 2000, 100)
C = plastic_concentration(r)
plt.figure(figsize=(8, 5))
plt.semilogy(r, C, 'b-', lw=2)
plt.xlabel('Distance from gyre center (km)')
plt.ylabel('Plastic concentration (particles/km²)')
plt.title('Microplastic Distribution in Ocean Gyre')
plt.grid(True, alpha=0.3)
# Annual plastic input estimate
annual_input = 8e6 # tonnes/year
plastic_density = 950 # kg/m³
avg_particle_mass = 1e-6 # kg (1 mg)
particles_per_year = annual_input * 1000 / avg_particle_mass
print(f"Estimated particles entering ocean per year: {particles_per_year:.2e}")