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Environment And Resources > Carbonate > Flashcards

Carbonate Flashcards

1
Q

Importance of ocean chemistry

A

Controls marine life distribution

Critical control on atmospheric gas concentrations and therefore climate and therefore sedimentary rock deposition

Salinity is a driver for ocean circulation

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2
Q

Neritic zone =

A

relatively shallow part of ocean above the drop off of the continental shelf

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3
Q

Pelagic zone =

A

Water column above open ocean, further divided by depth:

Epipelagic
Mesopelagic
Bathypelagic
Abyssalpelagic
Hadadlpelagic
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4
Q

Aphotic zone =

A

Little/no light

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5
Q

Littoral zone =

A

Intertidal zone

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6
Q

Sublittoral zone =

A

Permanently covered by seawater

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7
Q

Benthic zone =

A

Ecological region at the lowest level of the ocean

Species here = benthos

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8
Q

What do the rivers transport?

A

1) organic carbon
2) chemical weathering by-products
3) particulates

DEPENDS ON BEDROCK/EROSION TYPE DUE TO CLIMATE AND LATITUDE

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9
Q

Types of river

A

Precipitation dominated

Weathering dominated

Evaporation dominated

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10
Q

Precipitation dominated river

A

Rainfall controls composition

In low relief areas, can be far from sea

E.g. tropical rivers in Africa and S America

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11
Q

Weathering dominated rivers

A

Lots of dissolved species
In equilibrium with basins

E.g. tropical/subtropical rivers with moderate rainfall like Congo/Orinoco/Niger

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12
Q

Evaporation dominated rivers

A

Concentrated rainwater and dissolved species (high concentrations)

E.g. arid regions

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13
Q

Estuary =

A

Mixing zone of fresh water and seawater

An extreme salinity change on the system

  • causes PRECIPITATION
  • slow flow increases reaction time
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14
Q

Conservative behaviour =

A

Simple mixing

Straight line relationship

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15
Q

Non conservative behaviour =

A

Elements with a higher chemical reactivity have addition/subtraction FROM SOLUTION

Very high concentrations of some species found in flocculants

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16
Q

Non conservative - subtraction

A

Sorption
Flocculation
Precipitation
Biological activity

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17
Q

Non conservative - addition

A

Desorption

Dissolution

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18
Q

Atmospheric inputs

A

Aerosols
- fine particles of liquid or solid in the air

Gases

Deposition

  • wet = overland atmospheric water dissolves gas and particles
  • dry = particles in the air deposit without rain’s influence

DISSOLUTION OF GASES DIRECTLY FROM ATMOSPHERE - MOST IMPORTANT

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19
Q

Atmospheric inputs - examples

A

Canary Islands = lots of volcanic rocks
- dust fluxes from the desert with lots of nutrients

Saharan dust increases phytoplankton in the oceans

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20
Q

Hydrothermal inputs

A

Large input of material into oceans due to magma a high temperatures and percolation of sea water into hot sediments and rocks

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21
Q

Relative importance of sources

A

Rivers: surfaces and margins (dominate in coastal and open oceans)

Atmosphere: surface

Hydrothermal systems: deep water and mid ocean ridges

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22
Q

Henry’s law

A

At a constant temperature, the amount of given gas dissolved in a given volume of liquid is proportional to the partial pressure of that gas in equilibrium with that liquid

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23
Q

Carbonate species distribution in the oceans

A

Low pH = H2CO3

Medium pH = HCO3-

High pH = CO32-

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24
Q

Thermocline =

A

zone where there is a rapid temperature drop with depth

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25
Q

Lysocline =

A

Depth below which the dissolution of calcite increases dramatically

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26
Q

What does hydrogen bonding in seawater cause?

A

Higher boiling point and freezing point than expected

Can dissolve salts into ionic solution

  • breaks hydrogen bonding
  • increases ionic content
  • decreases volume

Largest SHC of any substance

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27
Q

Specific heat capacity =

A

The amount of energy required to raise the temperature of 1kg of a substance by 1 degree

  • if large can absorb and release more energy with small temperature changes
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28
Q

Latent heat =

A

Heat absorbed during changes of state

- large for water!!!

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29
Q

Physical properties of seawater

A

DENSITY
- increases until 4 degrees C then decreases

SALT
- dissolved salts lower the temperature of maximum density and the freezing point

PH
- slightly above 8 due to carbonate buffering effect

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30
Q

What causes variations in salinity?

A

Convection

Mixing

Evaporation

Precipitation

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31
Q

How does salinity vary?

A

Surface maximum at low and mid latitudes

Surface minimum at high latitudes

Low in tropics

Atlantic > Pacific (high T)

Fairly homogeneous in the deep sea

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32
Q

Potential temperature =

A

Temperature that would be acquired if a substance was adiabatically brought to standard reference pressure (usually 1 bar)

  • with increasing depth comes increasing pressure and the water is compressed
  • this exerts work as heat
  • small increase in T
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33
Q

Why is temperature important?

A

Controls reaction rates

Controls biological process rates

Controls water density

Controls the concentration of dissolved gases

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34
Q

Which are faster, ocean surface currents or deep ocean currents?

A

Surface

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35
Q

Conservative behaviour =

A

Residence time > mixing of ocean water

Thoroughly mixed = constant concentration with depth

36
Q

Non conservative behaviour

EXAMPLES

A

Concentration changes with depth DUE TO:

Biological activity
Decaying organic matter
Dissolution
Sorption
Hydrothermal inputs

EXAMPLE: Sodium

37
Q

Non conservative behaviour - recycled

EXAMPLES

A

Surface depletion
Depth enrichment

E.g. biolimiting constituents (photosynthesis/respiration/decomposition)
EXAMPLE: cadmium/phosphate/zinc/silicate

38
Q

Non conservative - scavenged

EXAMPLES

A

Surface enrichment
Depth depletion

E.g. atmosphere/river sources removed faster than the ocean’s circulation

EXAMPLE: lead

39
Q

Aluminium

A

Mid depth minimum

Strong atmosphere/river source

Removed into siliceous shells

Deep water source as sediments dissolve and flux of elements from hydrothermal systems

40
Q

Reductant =

A

Electron donor

Gets oxidised

41
Q

Oxidant =

A

Electron acceptor

Gets reduced

42
Q

Positive standard potential…

As reduction equations

A

Negative gibb’s free energy
Exothermic
»> RHS

STRONG OXIDISING AGENT

43
Q

Negative standard potential…

As reduction equations

A

Positive gibb’s free energy

44
Q

Natural water; positive standard potential

A

New species oxidised
Existing reduced

OXIDISING ENVIRONMENT

45
Q

Natural waters; negative standard potential

A

New species reduced
Existing oxidised

REDUCING ENVIRONMENT

46
Q

Oxic =

A

Measureable dissolved oxygen

47
Q

Suboxic =

A

Lack measurable oxygen or S2–, does have dissolved Fe

48
Q

Anoxic =

A

Has dissolved Fe and S2-

49
Q

Metal mobility

A

Redox states of metals and ligands determine solubility

Species distribution is a function of pH and pe

50
Q

Mn profiles in the oceans

A 
Mn4+ = insoluble and easily scavenged
Mn2+ = soluble

Dissolved manganese peaks at an oxygen minima i.e. in a reducing environment

51
Q

Why does oxygen increase at depth?

A

Due to mixing with cold waters containing more dissolved oxygen

BUT NOT ALWAYS THE CASE
- oceanic anoxia

52
Q

Oceanic anoxia

A

Due to Caribbean eruptions

  • increase nutrients
  • increase plankton
  • decay
  • food for organisms
  • respire and use oxygen

Can form a meromictic lake

Also done anthropogenically with fertilisers containing nitrates and phosphates

53
Q

Meromictic lake =

A 
Highly stratified body of water
Algae/nutrients/decay/respiration at the top
Anoxic at the bottom
- Black strata = organic matter
- preserved
COAL/OIL/GAS
54
Q

What limits productivity?

A

Carbon dioxide
- carbonate equilibrium supplies

Light
- allows photosynthesis to take place

Nutrients
- redfield ratio

55
Q

The Redfield Ratio =

A

Algae, as the most abundant organism and one of fixed elemental composition…
Represent the formula most life will want to operate at

C:N:P = 106:16:1

56
Q

Major nutrients

A

NITROGEN
inorganic (nitrate/ammonium)
Organic (organic compounds/particles)

PHOSPHOROUS
inorganic (orthophosphate PO4)
Organic (sorbed to particles)

SILICON
many diatoms require this for their shells

57
Q

Gyre =

A

Centre with little mixing and low productivity

58
Q

Upwelling =

A

Offshore currents causing high nutrient concentrations at the thermocline, brought from the bottom to the surface

59
Q

Productivity in polar lands vs polar oceans

A

Polar oceans most productive (no thermocline so nutrients are the same throughout)

Polar lands the least (less rapid nutrient release from Soil Organic Matter)

60
Q

What is productivity in the ocean affected by

A

Ocean upwelling

Nutrient provision

Latitude

61
Q

Where are some upwelling zones found?

A

Peru

Africa outer banks

North Pacific

California

North Africa

Antarctica

62
Q

Forms of ocean sedimentation

A

1) aeolian
2) fluvial
3) coastal erosion
4) volcanic ash clouds
5) biogenic debris
6) authigenesis
7) ice rafting
8) mass gravity flows
9) hydrothermal activity
10) submarine volcanism
11) high altitude jet streams
12) micrometeorites

63
Q

Sediment classification

A

GEOGRAPHIC DISTRIBUTION

WATER DEPTH

GRAIN SIZE

ORIGIN

SEDIMENTATION RATE

64
Q

Classification: geographic distribution

A

Neritic = on continental margin

Oceanic = overlaying oceanic crust

65
Q

Sediment classification: water depth

A

Neritic = continental shelf/coastal environments

Hemi pelagic = 200-3000m

Pelagic = >3000m

66
Q

Sediment classification: grain size

A

Clay: 0.12-3.9um

Silt: 3.9-125um

Sand: 0.125-2mm

67
Q

Sediment classification: origin

A

AUTHOGENIC/AUTOCHRONOUS

  • precipitate from solution
    1) hydrogenous (abiogenic)
    2) biogenous

ALLOCHRONOUS

  • carried into the sea as a solid phase
    1) lithogenous/terrigenous
    2) cosmogenous/extra terrestrial
68
Q

Sediment classification: sedimentation rate

A

Non pelagic = >1cm/1000yr

Pelagic = <1cm/1000yr

Relic = 0/less (NET dissolution)

69
Q

Types of deep sea sediments (A)

A

TRUE PELAGIC:

1: median <5um (except authigenic/biogenic)
2: less than 25% of particles >5um are terrigenous/volcanogenic/neritic

HEMIPELAGIC
- resedimented deep sea sediments

70
Q

Types of true pelagic sediments

A

Lithogenous
Biogenous
Hydrogenous
Cosmogenous

71
Q

Resedimentation processes

A

Slides and slumps

Debris flows

Turbidity currents

72
Q

Lithogenous

A

Terrigenous muds
RED CLAY

GREY MUD

From rivers and deserts

73
Q

Types of terrigenous muds

A

RED CLAY

  • montmorillonite/kaolinite/chlorite
  • 4000-5000m
  • nearly 1/2 of earth’s surface

GREY MUD
- has traces in it left by acorn worms and sea cucumbers

74
Q

Clays

Kaolinite and chlorite composition and location

A

Kaolinite

  • basic
  • tropical weathering
  • lower latitudes

Chlorite

  • physical weathering
  • higher latitudes

WEATHERING OF FELDSPARS

75
Q

Biogenous

A

Calcareous oozes

  • coccolithophore
  • foraminifers
  • “periplatform ooze”

Siliceous oozes
- radiolarians
- diatoms
N.B. Unlike carbonate, surface waters not supersaturated wrt silica so dissolution occurs more rapidly
Fecal pellets bring down faster than dissolution so they survive

76
Q

Cosmogenous sediments

A

Cosmic dust found in red clay
Common in South Pacific

Iron nickel and magnetite
50-200microns diameter
~300x10^3 tonnes fall on earth’s surface each year

77
Q

Hydrogenous

A

Formed directly from seawater in the pelagic zone (an oxygen environment)
Ion exchange and precipitation

E.g. ferromanganese nodules

78
Q

Turbidity currents =

A

Main agent for transporting shallow water sediment to deep waters

High density, sediment laden fluids

79
Q

Slides =

A

Move on bedding planes

Little internal deformation of moving mass

80
Q

Slumps =

A

Cut across bedding in rotational failures

Little internal deformation of moving mass

81
Q

Debris flows/mud flows =

A

Cohesive, viscous flows depositing debrites

82
Q

Submarine canyon =

A

Turbidity currents trigger flow and erodes surfaces forming a canyon with a fan at the bottom

83
Q

Bouma sequence

A

SANDS/LARGER GRAINS
- slow energy drop = graded

PARALLEL LAMINATED SANDS

  • upper flow regime
  • traction = flute casts

CROSS LAMINATED SANDS

  • lower flow regime
  • enough energy for saltation

PARALLEL LAMINATED SILTS
- slight current

MUD OFTEN BIOTURBATED
- suspension settling with no current

84
Q

Ice rafting, forms…

A

Morain deposits and U-shaped valleys

  • deposits a significant amount of material
  • associates with global climate events
85
Q

How do water’s physical properties help to regulate the earth’s climate?

A

Liquid to gas transition ABSORBS a lot of latent heat

Absorbs heat (evaporation) at low latitudes
Releases heat (condensation) at high latitudes

W/O this the contrast in temps would be large at poles vs equator

Environment And Resources (4 decks)

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