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Carbonate Flashcards

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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
Lysocline =
Depth below which the dissolution of calcite increases dramatically
26
What does hydrogen bonding in seawater cause?
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
27
Specific heat capacity =
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
28
Latent heat =
Heat absorbed during changes of state | - large for water!!!
29
Physical properties of seawater
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
30
What causes variations in salinity?
Convection Mixing Evaporation Precipitation
31
How does salinity vary?
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
32
Potential temperature =
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
33
Why is temperature important?
Controls reaction rates Controls biological process rates Controls water density Controls the concentration of dissolved gases
34
Which are faster, ocean surface currents or deep ocean currents?
Surface
35
Conservative behaviour =
Residence time > mixing of ocean water Thoroughly mixed = constant concentration with depth
36
Non conservative behaviour EXAMPLES
Concentration changes with depth DUE TO: ``` Biological activity Decaying organic matter Dissolution Sorption Hydrothermal inputs ``` EXAMPLE: Sodium
37
Non conservative behaviour - recycled | EXAMPLES
Surface depletion Depth enrichment E.g. biolimiting constituents (photosynthesis/respiration/decomposition) EXAMPLE: cadmium/phosphate/zinc/silicate
38
Non conservative - scavenged | EXAMPLES
Surface enrichment Depth depletion E.g. atmosphere/river sources removed faster than the ocean’s circulation EXAMPLE: lead
39
Aluminium
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
Reductant =
Electron donor | Gets oxidised
41
Oxidant =
Electron acceptor | Gets reduced
42
Positive standard potential... | As reduction equations
Negative gibb’s free energy Exothermic >>> RHS STRONG OXIDISING AGENT
43
Negative standard potential... | As reduction equations
Positive gibb’s free energy
44
Natural water; positive standard potential
New species oxidised Existing reduced OXIDISING ENVIRONMENT
45
Natural waters; negative standard potential
New species reduced Existing oxidised REDUCING ENVIRONMENT
46
Oxic =
Measureable dissolved oxygen
47
Suboxic =
Lack measurable oxygen or S2–, does have dissolved Fe
48
Anoxic =
Has dissolved Fe and S2-
49
Metal mobility
Redox states of metals and ligands determine solubility Species distribution is a function of pH and pe
50
Mn profiles in the oceans
``` Mn4+ = insoluble and easily scavenged Mn2+ = soluble ``` Dissolved manganese peaks at an oxygen minima i.e. in a reducing environment
51
Why does oxygen increase at depth?
Due to mixing with cold waters containing more dissolved oxygen BUT NOT ALWAYS THE CASE - oceanic anoxia
52
Oceanic anoxia
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
Meromictic lake =
``` 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
What limits productivity?
Carbon dioxide - carbonate equilibrium supplies Light - allows photosynthesis to take place Nutrients - redfield ratio
55
The Redfield Ratio =
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
Major nutrients
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
Gyre =
Centre with little mixing and low productivity
58
Upwelling =
Offshore currents causing high nutrient concentrations at the thermocline, brought from the bottom to the surface
59
Productivity in polar lands vs polar oceans
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
What is productivity in the ocean affected by
Ocean upwelling Nutrient provision Latitude
61
Where are some upwelling zones found?
Peru Africa outer banks North Pacific California North Africa Antarctica
62
Forms of ocean sedimentation
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
Sediment classification
GEOGRAPHIC DISTRIBUTION WATER DEPTH GRAIN SIZE ORIGIN SEDIMENTATION RATE
64
Classification: geographic distribution
Neritic = on continental margin Oceanic = overlaying oceanic crust
65
Sediment classification: water depth
Neritic = continental shelf/coastal environments Hemi pelagic = 200-3000m Pelagic = >3000m
66
Sediment classification: grain size
Clay: 0.12-3.9um Silt: 3.9-125um Sand: 0.125-2mm
67
Sediment classification: origin
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
Sediment classification: sedimentation rate
Non pelagic = >1cm/1000yr Pelagic = <1cm/1000yr Relic = 0/less (NET dissolution)
69
Types of deep sea sediments (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
Types of true pelagic sediments
Lithogenous Biogenous Hydrogenous Cosmogenous
71
Resedimentation processes
Slides and slumps Debris flows Turbidity currents
72
Lithogenous
Terrigenous muds RED CLAY GREY MUD From rivers and deserts
73
Types of terrigenous muds
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
Clays | Kaolinite and chlorite composition and location
Kaolinite - basic - tropical weathering - lower latitudes Chlorite - physical weathering - higher latitudes WEATHERING OF FELDSPARS
75
Biogenous
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
Cosmogenous sediments
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
Hydrogenous
Formed directly from seawater in the pelagic zone (an oxygen environment) Ion exchange and precipitation E.g. ferromanganese nodules
78
Turbidity currents =
Main agent for transporting shallow water sediment to deep waters High density, sediment laden fluids
79
Slides =
Move on bedding planes Little internal deformation of moving mass
80
Slumps =
Cut across bedding in rotational failures Little internal deformation of moving mass
81
Debris flows/mud flows =
Cohesive, viscous flows depositing debrites
82
Submarine canyon =
Turbidity currents trigger flow and erodes surfaces forming a canyon with a fan at the bottom
83
Bouma sequence
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
Ice rafting, forms...
Morain deposits and U-shaped valleys - deposits a significant amount of material - associates with global climate events
85
How do water's physical properties help to regulate the earth's climate?
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

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