BrainScapeDeck_EAE3311_2_20210309_172636

Question 1

Why would one sample sediments?

4 points.

Answer 1

• Sediment records on the ocean floor can be used to reconstruct past climates, land use, past ocean circulation patterns and global extinction events
• The sediments on the ocean floor can become lithified (e.g. limestone)
• Mineral resources (hydrocarbons, sand and gravel, REE, phosphate minerals
• Sediment transport and shoreline dynamics

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Question 2

How do we map sediment?

3 points.

Answer 2

• Seismic reflection profiles
• Isopach maps
• Ocean drilling

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Question 3

What are the primary factors that control distribution of ocean sediment?

5 points.

Answer 3

• Age of the underlying crust
• Tectonic history of the ocean crust
• Structural trends in basement
• Nature and location of sediment source, and
• Nature of the sedimentary processes delivering sediments to depocentres

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Question 4

What are sediments?

Answer 4

Eroded pieces of rock

Parts of living organisms

Minerals in water and outer space

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Question 5

Describe

Calcification?

4 points.

Answer 5

• Rapid diversification near the Precambrian–Cambrian boundary was closely accompanied by skeletonization which has been retained in marine environments to the Recent
• Calcium carbonate precipitation in the ocean is an important part of the oceanic and global carbon cycle.
• CO₃²⁻ + Ca²⁺ → CaCO₃ (and some inclusions Th, U, Ba…)
• C and O come from the oceanic pool

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Question 6

Where does most of the CaCO₃ come from?

2 points.

Answer 6

Most of the CaCO3 precipitation in today’s ocean is by

• Planktonic calcareous algae (Coccolithophores; Zondervan et al. 2001)
• Planktonic protozoa (Foraminifera; Barker and Elderfield 2002).

In the tropics, corals can contribute up to 40% of net calcification

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Question 7

Describe

What is Compensation Depth
(CCD)?

Answer 7

At the CCD, the rate of CaCO₃ input equals the rate of dissolution.

Below the CCD is where the red/brown clay (and in places, silica) accumulates.

Carbonate sand is mostly absent from the very deep sea.

Deep water holds more CO2, driving the calcification reaction towards dissolution

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Question 8

How is the CCD determined?

Answer 8

Thermodynamic calculations of solubility determine the depth of the CCD

It depends on pressure, salinity, and temperature, 3400-6000 m, (shallower in cold water)

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Question 9

What influences the settling velocity?

3 points.

Answer 9

• Buoyancy (difference in density between particle and fluid)
• Dynamic viscosity (The fluids internal resistance to flow i.e. resistance to shearing)
• Force of Gravity (F_g = (𝜌_p-𝜌_f) ⁴/₃ g𝜋R³)

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Question 10

What determins Biogenous sediment’s distribution?

3 points.

Answer 10

Biogenous sediment is one of the most common types of pelagic deposits

Distribution determined by:

• Productivity
• Destruction (dissolution)
• Dilution (by other sediment types)

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Question 11

Settling rate for Coccolithophore?

Answer 11

20 microns → 50 years to get the abyssal depths

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Question 12

Settling rate for Fecal pellet?

Answer 12

200 micron → 10-15 days to get the abyssal depths

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Question 13

What is a key impact of the different sizes of biogenous sediment?

Answer 13

The biogenic ooze is 99% made up of fecal pellets

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