Lesson 6: Exploring the Seafloor

Bathymetry Definition: Underwater topography Only 10% of ocean has been mapped As varied as the land’s surface Contains Earth’s tallest mountain Contains Earth’s widest plains Contains Earth’s deepest valleys

Bathymetry Definition: Underwater topography Only 10% of ocean has been mapped Earth’s final frontier As varied as the land’s surface Contains Earth’s tallest mountain (Mauna Kea) Contains Earth’s widest plains Contains Earth’s deepest valleys (Mariana Trench)

How is the topography mapped?

Instruments Used 1. Plumb lines

Instruments Used 2. SONAR (Sound Navigation & Ranging) * Utilizes knowledge of speed of sound in water * Equation: Sea Depth = ½ TV T – time for sound to return to transmitter V – velocity of sound in water (1500 m/sec) * 2 types : a) side scan b) multibeam

Instruments Used Dragged behind ship Image related to echo’s intensity Side scan Multibeam Dragged behind ship Image related to echo’s intensity Pulse emitted from ship’s hull Image related to echo’s travel time

Instruments Used 3. Orbiting satellites * sea surface is directly related to seafloor features

Figure 6.29 Identify each seafloor feature represented with the letters

Figure 6.29 A – Continental shelf B – Continental slope C – Continental rise D – Abyssal plain E – Seamounts F – Mid-ocean ridge G – Trench H – Submarine canyon

Figure 6.30

Figure 6.31 Describe the topography of the seafloor near the Mississippi River Delta in the Gulf of Mexico

Figure 6.32 Name two seafloor features that are evident in this image.

Give one similarity and one difference

Seafloor sediment

Seafloor Sediment What is sediment? 4 types seen in the ocean a) terrigenous sediment * originates from land * primarily abiotic materials * erosion carries particles downstream to the ocean (watershed) * composition based on where the sediment originates

Seafloor Sediment 4 types seen in the ocean b) biogenous sediment * originates from living organisms * primarily phytoplankton *also weathering & erosion of coral reefs

Seafloor Sediment 4 types seen in the ocean c) hydrogenous sediment * originates as precipitates out of seawater * contains many minerals d) cosmogenous sediment * originates from space

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Why study bathymetry?

Bathymetry influences where marine organisms live Gray Seal Southern Elephant Seal