The Ocean Floor

Description of Bottom Topography

Atlantic Ocean Continental Shelf

Typical Oceanic Profile continental margin ocean basin coastal region oceanic ridge continental shelf Slope Abyssal plain Depth > 4000 m

The Continental Margin ocean basin shelf break coastal region oceanic ridge continental shelf Slope Abyssal plain continental rise > 4000 m

Continental Margin Fig. 2-3a

Continental Shelf

Coastal Region • Includes: •beaches •estuaries • lagoons • marshes • deltas coastal region Most important region to humans And marine birds and mammals

Beaches

Typical Salt Marsh

Mangrove Swamp

Continental Shelf less than 0.1° angle • Definition: shallow part of ocean bottom next to coastline continental margin • SLOPE is less than 0.1° angle continental shelf Slope continental rise

Most exposed in Pleistocene

Continental Slope and Rise • Slope is 1° to 6° • Rise: less than 1° Rise is about 20 km in Atlantic along passive margins Can be absent altogether in active margins with trenches. • Slope & rise can be cut by submarine canyons Slope Continental rise

Overlapping fans=cones See Fig. 2-3a

San Lucas Submarine Canyon 2 meters

Typical Oceanic Profile continental margin ocean basin shelf break oceanic ridge continental shelf Slope Abyssal plain continental rise

Are the deep flat areas of the ocean Ocean Basins Are the deep flat areas of the ocean

Deep Ocean Basins Fig. 2-3b

May rise above the surface Seamounts and Guyots- undersea mountains that rise more than 1 km from the seafloor SEAMOUNT Top is rounded May rise above the surface and form an island GUYOT Top flattened by waves

3 Major Oceanic Ridges Mid-Atlantic Ridge Carlsberg Ridge E. Pacific Rise

The largest is the Mid Atlantic Ridge half that separatat Characteristics of Oceanic Mountain Ridges • Total length: 60,000 km • Present in all oceans • Between 1,000 and 4,000 km wide • mountains are 2 - 4 km high The largest is the Mid Atlantic Ridge half that separatat

Mid-Ocean Ridges Fig. 2-3c

Mid-Atlantic Ridge Shallow valleys 20 - 30 km wide with high volcanic activity

Oceanic Trenches • 31 in the world; • Deep; U or V shaped •These form the deepest places on Earth • Max 130 km wide, 1500 km long

Distribution of Trenches

Kurile 10,500 m Mariana 11,000 m Tonga 10,880 m 3 _________ trenches

Island Arcs are associated with volcanoes

Atlantic Ocean Pacific Ocean shelf slope hills Ridge plains island arc seamounts ridge plain trench Pacific Ocean

HYDROTHERMAL VENTS or BLACK SMOKERS At a hydrothermal vent, sea water that has sunken into cracks in the ocean crust and been heated (sometimes to over 180 degrees!) by the interior of the earth escapes through crust cracks back into the ocean. http://www.pmel.noaa.gov/vents/nemo/explorer/multimedia.html

The superheated water beneath the oceanic crust often dissolves minerals from nearby rocks. The precipitating minerals often give vent fluids different colored “smoky” appearances.

As hot vent fluids meet cold ocean water, minerals precipitate (fall) out of vent fluids. The precipitating minerals form “chimneys” and other formations on the sea floor.

Hydrothermal Vent Sites