4.6 Deep-Sea Life
The deep sea (below 200m) is Earth's largest habitat, covering 65% of the planet. Despite extreme conditions—no light, high pressure, cold—it supports diverse and bizarre life forms.
Extreme Conditions
No Sunlight
Below 1000m: total darkness. Bioluminescence only light source.
High Pressure
1 atm per 10m depth. At 4000m: 400 atm (crushing for surface life).
Cold Temperature
1-4°C throughout deep ocean. Slows metabolism, extends lifespan.
Food Scarcity
Depends on "marine snow" (sinking organic matter). Very low energy input.
Bioluminescence
\( \text{Luciferin} + O_2 \xrightarrow{\text{luciferase}} \text{Oxyluciferin} + h\nu \)
Chemical light production. 90% of deep-sea animals are bioluminescent.
Attraction
Lure prey (anglerfish)
Defense
Startle predators
Communication
Find mates
Hydrothermal Vent Communities
Islands of life powered by chemosynthesis, not photosynthesis:
Giant Tube Worms
Riftia pachyptila. No mouth/gut. Symbiotic bacteria oxidize H₂S.
Vent Shrimp
Rimicaris exoculata. "See" infrared from hot vents. Bacteria on gills.
Chemosynthesis
H₂S + CO₂ → organic carbon. Independent of solar energy.
Python: Pressure & Depth
#!/usr/bin/env python3
"""deep_sea_life.py - Deep-sea pressure and light"""
import numpy as np
import matplotlib.pyplot as plt
def pressure_at_depth(z):
"""Pressure (atm) at depth z (m)"""
return 1 + z / 10.33 # 1 atm + hydrostatic pressure
def light_at_depth(z, k=0.05, I0=1):
"""Light intensity (fraction) at depth z (m)"""
return I0 * np.exp(-k * z)
z = np.linspace(0, 11000, 1000) # To Challenger Deep
fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(12, 6))
# Pressure
ax1.plot(pressure_at_depth(z), z, 'r-', lw=2)
ax1.set_xlabel('Pressure (atm)')
ax1.set_ylabel('Depth (m)')
ax1.set_title('Pressure vs Depth')
ax1.invert_yaxis()
ax1.axhline(10994, color='b', linestyle='--', label='Challenger Deep')
ax1.legend()
# Light
z_light = np.linspace(0, 1000, 100)
ax2.plot(light_at_depth(z_light)*100, z_light, 'g-', lw=2)
ax2.set_xlabel('Light (%)')
ax2.set_title('Light Penetration')
ax2.invert_yaxis()
ax2.axhline(200, color='orange', linestyle='--', label='Euphotic zone')
ax2.axhline(1000, color='purple', linestyle='--', label='Aphotic zone')
ax2.legend()
plt.tight_layout()
print(f"Pressure at Mariana Trench (10994m): {pressure_at_depth(10994):.0f} atm")
print(f"Light at 200m: {light_at_depth(200)*100:.4f}%")