Chapter #7 Silica & Redfield Ratios

How much silica is found in the earth's crust?

58%, as Silica Dioxide (SiO2)

What are two common compounds of silica in the ocean?

Crystalline quartz and Amorphous silica.

What is the estimated accumulation rate of silica?

It's the sum of accumulation rate estimates for all pelagic sedimentation.

What are the forms of silica in seawater?

Particulate (biologic structures) and Dissolved (Silicic Acid).

How does dissolved silica form a polymer?

When the medium becomes supersaturated, monomers combine to form polymer chains.

Why are waters undersaturated in silica?

Concentration is less than the solubility.

What is the solubility value of amorphous silica?

Estimates at 1800 microM at 25 degrees C.

What is the solubility value of quartz?

Estimates at 100 microM at 25 degrees C.

What increases the solubility of silica?

Increase in temperature, pressure, and alkaline pH.

What are chert deposits?

Fine-grained, dense, hard rocks consisting of amorphous silica and microcrystalline quartz.

What factors control silica concentrations in the sea?

Uptake by organisms, terrestrial input, sedimentation, and dissolution of biogenic silica.

What is the source of the transfer gradient silica in sediments?

Dissolution of buried siliceous organisms.

What are the silica profiles in the Atlantic Ocean?

Gradual increase from N to S in North Atlantic Deep Water, low at surface, high in Atlantic Intermediate Waters.

What are the silica profiles in the Pacific Ocean?

Higher concentrations than the Atlantic, increasing from S to N in deep waters.

Does silica follow the same pattern as nitrogen and phosphorus in relation to oxygen?

Silica has an inverse correlation to oxygen profiles.

What is the Redfield ratio?

The concentration ratios of elements, typically 16:1 for N and P.

What is the Redfield Molecule?

Representation of oxidation states of common carbohydrates (not a real molecule).

What does the equation 106 CO2 + 122 H2O + 16 HNO3 + H3PO4 refer to?

Photosynthesis and respiration.

What is the Redfield Ratio at chemical equilibrium?

1P = 16 N = 124 C = 166 O2 = 23 Si.

What is the Photosynthesis Quotient?

The ratio of Oxygen produced to Carbon Dioxide fixed.

What is the Respiration Quotient?

Ratio of Oxygen consumed to Carbon Dioxide evolved.

How can the Redfield ratios be used for conversions?

To find equivalent chemical concentrations of other elements.

How can the Redfield ratio determine limiting nutrients?

By comparing measured ratios to the Redfield ratio.

What is Potential Fertility?

The amount of organic matter that could be produced in photosynthesis per unit volume.

What does it mean if the N:P ratio is less than 16:1?

Nitrogen is limiting.

What does it mean if the Atlantic has higher Redfield ratios than the Pacific?

Nitrogen is a limiting factor in the Pacific.

Which ocean is a source of Nitrogen?

Atlantic is a source; Pacific is a sink.

Are coastal and gulf water N:P concentrations greater or lower than the Redfield ratio?

Lower, so Nitrogen is limiting.

What are Initial/Preformed Nutrients?

Nutrients already in seawater before or during downwelling.

What causes low concentrations of nutrients in surface waters?

Uptake followed by downward transport of organic debris.

What can lead to different nutrient concentrations in deep water of different ocean basins?

Large-scale ocean circulation.

What do departures from the Redfield ratio indicate?

The nature of oceanic processes.

What are the ratios of Nitrogen to Phosphate generally present in deep waters?

14N:1P to 17N:1P.