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Isotope Geochemistry > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

What is the ice volume effect?

A

when its warm glaciers are small so water has a high 18O

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2
Q

Are glaciers isotopically light or heavy?

A

light

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3
Q

Are oceans heavy or light during cold period?

A

heavy

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4
Q

What is the temperature effect?

A

As calcium carbonate forms fractionation increases

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5
Q

What does 18O of calcite depend on?

A

avg age of ocean, temp of H2O during growth, vital effects, local water 18O

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6
Q

What is a milankovitch cycle?

A

the earths orbit around the sun is not perfectly round, so there are changes in how the sun strikes the N hemi in the summer (eccentricity), and seasonal changes from earths rotational axis not being perdendicular to the orbital plane (obliquity)

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7
Q

Is solar forcing strong and does it match stages of glaciation?

A

Solar forcing is weak and does not match stages of glaciation

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8
Q

Give example of a positive feedback

A

Ice sheet grows, albedo increases (making earth colder), and then ice sheets grow more continuing the cycle

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9
Q

Give an example of a negative feedback

A

The earth warms, then rock weathering increases drawing down CO2, and then warming slows

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10
Q

What drives glacial cycles?

A

Milinkovich forcings

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11
Q

What happens with north atlantic deep water?

A

draws warm water north, during a glacial deep water weakens and thus weakens warming in the noth

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12
Q

What happens to calcite when is gets colder?

A

calcite gets heavier

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13
Q

how do greenland ice cores compare to antarctic ice cores?

A

very similar

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14
Q

how do cretaceous soil clays compare to modern precip (18O)?

A

soil : 22-15 per mil, precip.: -5 to -15 per mil

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15
Q

when would calcite not track precip?

A

when its too acidic in lakes

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16
Q

at higher temp are we more or less likely to get close to equili.?

A

more likely

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17
Q

how does isotopic fract change w/temp?

A

fract decreases as temp increases

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18
Q

Why does quartz and magnetite have the biggest fractionation?

A

magnetite is a Fe oxide with long bonds and low energy whereas quartz has short bonds and strong energy

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19
Q

What does site potential equal?

A

bond strength

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20
Q

what is the order of mineral site potential from lowest to highest?

A

Carbonates, silicates, oxides

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21
Q

How does SO4- fract. compare to SO2 and S2-?

A

SO4- is heavier b/c is has a high valence with shorter stiffer bonds

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22
Q

What is the equation for 2 mins formed from the same fluid?

A

delta = A + B/T^2

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23
Q

How can we use assimilated materials to finger print exotic materials?

A

they have a higher 18O

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24
Q

What is the mantles 18O?

A

5.2 per mil

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25
How much heavier is cpx than olv.?
0.3 per mil
26
How can we use 10O and Sr to understand magma?
We can look at crustal and source contamination
27
are sediment 18O and Sr heavy or light?
heavy
28
If dissolution is greater than precipitation?
Water 18O gets heavier, and rock gets lighter
29
Where does lots of dissolution lie relative to the global meteoric water line?
Shift to right
30
what is precip. is greater than dissolution?
H2O gets lighter and rock gets heavier
31
What is the mixing equation?
delta = X(a)delta(a) + X(b)delta(b)
32
What is the 18O for sediment contamination?
+14 per mil
33
If there is a heavy isotope in a molecule how does this effect stability?
the symmetry breaks so we gain stability
34
What was sulfur variable 2Ga ago?
mass independent fract., there was sulfur dioxide and not a lot of oxygen
35
what can we use delta17O for?
to study O3 related rxns (ozone)
36
what can we use delta33S for?
to study atmosphere, paleo-oxidation
37
What Hg are mass dependent and why?
204 and 200 bc even numbers dont have spin
38
Is Hg heavier in coastal or oceanic environments?
oceanic
39
What does energy change depend on in a redox rxn?
nucleus size
40
What is the nuclear volume effect?
heavy isotopes have electrons inside the nucleus so coulomb potential energy doesnt go down
41
What is self shielding?
The more abundant an isotope is the more it is shielded
41
WHat is the E for diffusion on C in/out of a C3 plant?
less than 4.4 per mil
42
E equation for photsynthesis
4.4 + (29.4 - 4.4)(Cin/Cout)
43
What is the E for carboxylation inside a C3 plant?
29.4 per mil (isotopically light) remember carbon is flipped
44
What is the E value for C3 plants
16-26 per mil (isotopically light)
45
What is the atmospheric E value of CO2?
-7 per mil
46
Are CO2 plants strongly fract. compared to the atmos?
Yes
47
How are C4 plants diff than C3
manage carbon with stoma that bring carbon into bundled sheet cells
48
Where is equili. fract in a C4 plant?
CO2 in to HCO3-
49
What is the E for C4 plants?
4 per mil
50
What is the E for CAM plants?
4-26 per mil
51
What is the E for marine algae?
10-5 per mil
52
is organic matter isotopically light or heavy?
light
53
What does burial of organic matter do?
removes C and increases O2 in the atmos.
54
WHat is limestone/bicarb 13C?
0 per mil
55
What is reduced carbon 13C?
-26 per mil
56
How is atmos 13C evolving over time?
getting lighter (-7 to -8 per mil)
57
What does photosynthesis do ocean isotopes?
Drives them heavier bc photosynthesis takes the light isotopes and buries them
58
What is the biological pump?
Diff. btwn surface dwelling (planktonic) and bottom dwelling organisms (benthic) due to paleoproductivity
59
What if paleoproductivity is high?
Drives down CO2 in atmosphere
60
What should we measure to get PCO2 of surface ocean?
HTCD (13C org matter) and forams (13C of H2O) NO TOC
61
WHat is 13C of ocean?
+0.6 per mil
62
What is 13C of carbonate sed.?
+1 per mil
63
What is 13C of sed. org. carbon?
-20 per mil
64
What is 13C of volcanoes?
-6 per mil
65
What happened to 13C of the ocean during the End-K extinction
got lighter. paleoproductivity went down
66
When was 13C the highest?
carboniferous
67
What do C and N relate to animal food sources?
only slightly heavier than the diet
68
How do N and C vary with C3 and C4 plants?
C3 (N heavy, C light), C4 (N heavy, C heavy)
69
WHat if a person goes from eating corn to eating legumes?
their isotopes will get lighter
70
What is the E for denitrification?
-5 to -40 per mil
71
WHat is the E for nitrification?
-12 to -29 per mil
72
WHy are shifts in E small during nitrification?
ammonium is bound strongly to solids
73
Is NH3 enriched in light or heavy isotopes?
light
74
What is the delta for equili. fract. of NH3 and NH4+?
33 per mil
75
What is the E for microbial sulfate reduction?
-2 to 18 per mil (usually light)
76
When do we see little fract. of S?
precip. of sulfate minerals, and uptake by higher plants or algae
77
WHat has a greater E: sulfide or sulfate burial?
sulfide
78
What is the E for chromate reduction?
-2 to -4 per mil (product is light)
79
WHat happens to Cr 1Ga ago?
gets a +6 valence because of oxgyen increase
80
What is the E for selenate reduction?
2-12 per mil (prod. is light)
81
What elements can we detect reduction with?
Se and Cr
82
Where did banded iron formations come from?
Fe oxidation from photsynthesis
83
What do we use Mo for?
to estimate sulfur bearing water
84
What are the delta for burial of Mn/Fe oxides vs sulfudic H2O?
Mn/Fe = -3 per mil Sulfidic = small
85
What can cause fract at high temp?
Diffusion and bond changes
86
What isotope is enriched in the hot end of a thermal gradient?
light isotope
87
Which B is dominant at low pH?
B(OH)3 (40 per mil) with B(OH)4- (20 per mil)
88
WHich B is dominant at high pH?
B(OH)4-
89
WHats the diff betwn Li in the dissolved and mineral form?
dissolved; heavier (4 fold) mineral; lighter (6 fold)
90
Why does Li have an upward trend in the paleocene?
weathering

Isotope Geochemistry (2 decks)

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