General stable isotopic knowledge

Question 1

nuclide

Answer 1

a general term for a specific isotope

Question 2

isotopologue

Answer 2

molecules that differ from one another only in their isotopic composition, e.g., 12CO2 and 13CO2. Can have same or different masses from one another.

Question 3

The six elements for which stable isotope chemistry relates

Answer 3

C, N, O, S, Cl, H

Question 4

Kinetic isotope effects

Answer 4

Type of isotope effects assoc’d with fast, unidirectional, incomplete processes e.g., evaporation, diffusion, dissociation, and almost ll biological reactions. Results from different translational velocities of the respective isotopes involved

Question 5

Molecules containing the heavier isotope are __ stable and have ___ dissociation energies than those containing the light isotopes

Answer 5

1. more

2. higher

Question 6

Equilibrium isotope effects

Answer 6

Type of isotope effects assoc’d with the effect of atomic mass on bond energy. Internal energies of different isotopes, resulting in a subtle pref for heavy isotope to be partitioned into one phase rel to another. e.g., temperature dependence of fractionationg such as water and a precipitating phase e.g., biogenic carbonate

Question 7

Isotopomer

Answer 7

Term for isotopologues that differ from one another only in the positions or locations of the isotopic elemnts

Question 8

Isotope exchange reactions

Answer 8

equilibrium reactions in which isotopes of a single element are exchanged between two substances

Question 9

Five components of a gas source IRMS

Answer 9

1) gas inlet system
2) ion source
3) flight tube
4) ion collector
5) recording system

Question 10

Two biggest fundamental changes that improved IRMS sensitivity for use in natural abundance isotopes

Answer 10

1) substituting a vastly more sensitive electrometer to intensify beam signals
2) introducing an ingenious magnetic valve switching mechanism that allowed rapid switching from std gas to uknown gas in the source of the mass spec

Question 11

Why we need viscous flow in the mass spec

Answer 11

to assure no fractionation occurs when gas exit from the capilaries into the source of the spectrometer. i.e., avoid molecular flow.

Question 12

Continuous flow method of IRMS

Answer 12

Improvement over dual-inlet method. Samples of gas are entrained in helium stream, purified in a gas chrmotograph, introduced directly in to the source.

Question 13

Time frame of steady state equilibrium of C

Answer 13

200,000 years

Question 14

Effect of light limitation on epsilon, E, for nitrate consumption?

Answer 14

This environmental variable INCREASES epsilon, E, of nitrate consumption.

Question 15

percentage of DIC that is CO2 at pH =8.2?

Answer 15

1%

Question 16

percentage of DIC that is H2CO3 at pH =8.2?

Answer 16

<0.003?

Question 17

percentage of DIC that is HCO3- at pH =8.2?

Answer 17

~ 91%

Question 18

percentage of DIC that is CO3(2-) at pH =8.2?

Answer 18

~ 8%

Question 19

d13C ‰ of C3 plants?

Answer 19

-31 to -21‰ (i.e., lower than C4 plants)

Question 20

d13C ‰ of C4 plants?

Answer 20

-15 to -10‰ (i.e., higher than C3 plants – less negative)

Question 21

d13C ‰ of marine plankton?

Answer 21

-30 to -18‰ (i.e., around C3 plants ish)

Question 22

d13C ‰ of atmospheric CO2

Answer 22

-8 to 9‰

Question 23

Marine Carbonates, d13C ‰ of

Answer 23

-1 to 2‰

Question 24

does epsilon between DIC and CO3 or CO2 (aq) increase or decrease with increasing temperature?

Answer 24

decreasing epsilon with increasing temperature (see figure from Sigman class notes, with HC03- as the horizontal bar at the top). Note, see figure too, but basically CO2(g) is actually higher than CO2(aq), unlike the water vapor effect. NOTE: epsilon is actually greatest between HCO3 and CO2, as opposed to aqueous vs gaseous CO2

Question 25

Percentage of water volume in ice caps

Answer 25

2.5%

Question 26

exchange rate of atlantic

Answer 26

In the order of 100 years

Question 27

What percentage of all natural waters is ocean?

Answer 27

97%

Question 28

Evaporation from the surface preferentially removes light _____ of water and increases the salinity, so values of both d18O and S of surface water increase with increasing degree of evaporation.

Answer 28

isotopologues!

Question 29

Typical value of glacial waters, d18O =

Answer 29

-30‰ (very low)

Question 30

Typical value of rivers in temperate zones, d18O =

Answer 30

-4.7‰ (i.e., much higher i.e, much less negative than glacial waters)

Question 31

Where are the lowest d18O values of water vapor found and why?

Answer 31

region of the trade winds… between 18 and 26º latitudes, where evap is highest and humidity is lowest. Note: evaporation has kinetic isotope effect, especially in low humidity as water vapor formation is non reversible. p 105 Sharpe.

Question 32

Amount effects. And also freezing wggects

Answer 32

See p 65 your notes

Question 33

How many cm per 1000 yrs in seds?

Answer 33

10 cm

Question 34

How many cm per 1000 yrs in ice?

Answer 34

On the scale of ~ meters

Question 35

Freezing affects the ____ but not the ____

Answer 35

Freezing affects the SALINITY but NOT the d18O of ocean water

Question 36

D18O of atmospheric O2

Answer 36

23.5 permil (Danny, class notes)