2.3 Submarine topography and bathymetry

The ocean floor is a hidden world of diverse landscapes. From shallow continental shelves to deep abyssal plains, it's shaped by tectonic forces, volcanic activity, and sedimentation. These processes create features like mid-ocean ridges, seamounts, and trenches.

Mapping the seafloor is crucial for understanding its topography. Scientists use echo sounding, satellite altimetry, and underwater vehicles to create detailed maps. These reveal the complex terrain beneath the waves, helping us interpret geological processes and uncover the ocean's secrets.

Ocean Floor Topography

Features of ocean floor topography

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• Continental margins extend from shoreline to deep ocean basin
  • Continental shelf gently slopes from coast to ~200m depth
  • Continental slope steeply descends to ~3000m depth
  • Continental rise gradually transitions to abyssal plain
• Deep ocean basins cover majority of seafloor
  • Abyssal plains form vast flat areas at 3000-6000m depth
  • Mid-ocean ridges create underwater mountain chains (Mid-Atlantic Ridge)
  • Seamounts rise from seafloor as isolated underwater volcanoes
  • Oceanic plateaus form large elevated areas (Ontong Java Plateau)
• Trenches mark deepest parts of ocean
  • Subduction zones where oceanic crust sinks into mantle
  • Challenger Deep in Mariana Trench reaches ~11,000m depth

Formation of submarine features

• Plate tectonics drive major seafloor processes
  • Seafloor spreading creates new oceanic crust at mid-ocean ridges
  • Subduction recycles old oceanic crust at trenches
  • Continental drift shapes global ocean basin configuration
• Volcanic activity builds underwater structures
  • Hotspots form island chains as plates move over stationary plumes (Hawaiian Islands)
  • Underwater volcanoes create seamounts and guyots
• Sedimentation accumulates material on ocean floor
  • Turbidity currents transport sediment down continental slopes
  • Pelagic sedimentation slowly deposits material from water column
• Erosion shapes continental margins
  • Submarine canyons carved by turbidity currents
  • Wave action modifies continental shelves
• Isostatic adjustment alters vertical position of crust
  • Glacial rebound lifts land after ice sheet melting
  • Crustal loading and unloading from sediment deposition/erosion

Bathymetric Mapping and Interpretation

Ocean floor mapping techniques

• Echo sounding uses sound waves to measure depth
  • Single-beam echo sounders provide point measurements
  • Multibeam echo sounders create wide swath of depth data
  • Side-scan sonar produces detailed images of seafloor texture
• Satellite altimetry measures sea surface height
  • Radar detects subtle variations in ocean surface
  • Gravity anomalies reveal underlying seafloor topography
• Seismic reflection profiling images sub-seafloor structures
• Underwater vehicles collect high-resolution data
  • Remotely operated vehicles (ROVs) controlled from surface
  • Autonomous underwater vehicles (AUVs) operate independently
• Light Detection and Ranging (LiDAR) maps shallow coastal areas

Interpretation of bathymetric data

• Bathymetric contour lines represent equal depths
  • Depth intervals typically 100-1000m
  • Closely spaced lines indicate steep slopes
• Color-coded depth maps provide visual representation
• Cross-sectional profiles show vertical slices of seafloor
  • Vertical exaggeration emphasizes subtle features
• Identifying submarine features from bathymetric data
  • Seamounts appear as isolated peaks
  • Submarine canyons form V-shaped incisions on continental slopes
  • Fracture zones create linear offsets in mid-ocean ridges
• Bathymetric data analysis techniques
  • Digital elevation models (DEMs) create 3D representations
  • 3D visualization enhances interpretation of complex topography
• Relating bathymetry to geological processes
  • Tectonic plate boundaries visible as linear features
  • Sedimentary processes revealed by smooth vs. rough textures