Geological Oceanography

What are the two types of crust and their compositions?

Oceanic crust - basaltic, dense, thin

Continental crust - less dense, thick

The earths magnetic field changes polarity with time, how do we know this?

Volcanic rocks erupt lava flows containing magnetic particles, when the flow solidifies, these particles line up in the direction of the magnetic field.

How did continental drift occur?

Mid ocean ridges erupt lava, this pushes tectonic plates apart and causes seafloor spreading. Oceanic crust is youngest at the ridge.

What happens to old oceanic crust?

It is consumed into the mantle

How do we know what is below the surface of the ocean?

An explosion is set off and sound waves bounce of the rocks and penetrate below the surface. The time delay back to the receiver allows an image of what is below the surface.

What are the different ocean environments?

Continental shelf - contains sediments from when sea level is low

Continental slope

Continental rise - transition to the deep sea floor

Abyssal plain - a flat plain as the sea floor has been covered with sediments

What are transform faults and how do they occur?

They are when blocks slide past each other. This is caused as mid ocean ridges spread at different rates across the length. Thus there is fractures in the ridge to allow for different spreading times, and plates can then slide across each other.

How are atolls formed and what are they?

Atolls are a ring shaped reef. As long as the sea floor doesn’t submerge too quickly, the reef will continue to grow on top of itself.

What is ooze?

Things that settle to the seafloor after death and accumulate.

What is biogenic ooze?

Microscopic planktonic fossil remains. It is considered biogenic if more than 30% of the ooze is organic. The two types are siliceous and calcareous.

What is siliceous ooze and where does it occur?

Hydrated silica. Made up of diatoms and radiolaria. It occurs in areas of upwelling as these areas are nutrient rich.

What is calcareous ooze?

Calcite. Made up of foraminifers, coccolithophores, and pteropods.

What is the carbonate compensation depth?

The depth where rate of dissolution = rate of supply.

How is ocean pH regulated?

Carbonic acid makes bicarbonate which makes calcite. This process releases two hydrogen ions, decreasing pH. When organisms die, the calcite is dissolved and the reaction is reversed.

Solubility pump

Cold saline waters sink due to change in density and temperature. This sucks the atmosphere with it, increasing CO2 in deep waters. The bottom waters well up, returning CO2 to the atmosphere.

Biological pump

Rapid CO2 transfer. Organisms in upper ocean use CO2 for photosynthesis, this draws more CO2 into the water. When these organisms die, they decay and release CO2 back into the atmosphere.

What are the three deep sea mining deposits that spark interest?

Cobalt crusts

manganese nodules

Seafloor sulfides

What are cobalt crusts?

They are made up of iron and manganese and are found at seamounts in the deep ocean. These require currents and sediment free surfaces, they take millions of years to grow.

What are manganese nodules?

Balls of manganese and iron formed around a nucleus, they are found on abyssal plains in oxygenated deep waters.

What are seafloor massive sulfides?

These are found at hydrothermal vents. Water travels beneath the surface and becomes hot and mixes with metals. This is erupted.