Atlantic Ocean Floor: Sediments, Not Soil

The Atlantic Ocean does not have soil—a terrestrial concept defined as a biologically active, structured medium of minerals, organic matter, water, and air supporting plant growth. Instead, the ocean floor is covered by marine sediments that vary by depth, location, and geological history.

Atlantic Seafloor Sediment Types

1. Terrigenous Sediments (Land-Derived)

• Sources: River discharge (Amazon, Congo, Mississippi, Hudson), glacial flour, wind-blown dust (Sahara → Atlantic), coastal erosion
• Distribution: Continental shelves, slopes, rises; thick near mouths (Amazon cone: 10+ km)
• Composition: Quartz, clays (smectite, illite, kaolinite), rock fragments

2. Biogenic Sediments (Organism-Derived)

• Calcareous Ooze: Foraminifera, coccolithophores, pteropods — above CCD (Calcite Compensation Depth, ~4,500 m); covers mid-ocean ridges, plateaus
• Siliceous Ooze: Diatoms, radiolarians — high-productivity zones (equatorial upwelling, Southern Ocean); below CCD
• Distribution: "Ooze belts" mapping surface productivity

3. Authigenic/Hydrogenous Sediments

• Manganese Nodules: Abyssal plains (hydrogenous precipitation); Co, Ni, Cu, REEs — mining interest
• Phosphorites: Upwelling zones (Namibia, Peru margins)
• Metal Sulfides: Hydrothermal vents (Mid-Atlantic Ridge)

4. Volcanic/Volcaniclastic

• Ash layers (tephra) from eruptions (Iceland, Azores, Caribbean, Mid-Atlantic Ridge)
• Basaltic glass, palagonite — ridge flanks, seamounts

5. Glacial-Marine (High Latitudes)

• Diamictons, dropstones (ice-rafted debris) — Labrador Sea, Nordic Seas, Antarctic margin

Sediment Thickness

• Shelves: 0-1 km (recent, reworked)
• Abyssal Plains: 1-3 km (accumulated over millions of years)
• Continental Rises: 5-10+ km (turbidite sequences, fans — Amazon, Congo, Mississippi)
• Oceanic Crust: Zero at ridge axis; increases with age (100-300 m/Myr)

Why Not "Soil"?

• No pedogenesis (soil formation processes: horizons, organic-mineral mixing, bioturbation by roots/earthworms)
• No vascular plants (except seagrasses in shallow photic zones — distinct "blue carbon" sediments)
• Different timescales: sedimentation (mm/kyr) vs. pedogenesis (cm/kyr)

Marine sediments are Earth's largest geological archive—recording climate, oceanography, volcanism, and life history. Calling them "soil" obscures their distinct origin, properties, and scientific value.