Term 1 Isotopes & Climate Questions

Question 1

How does isotope weight impact energy gain?

Answer 1

Heavier molecules have stronger bonds and are harder to bump up in energy level

Question 2

Which isotope is preferentially used in reactions, and therefore more common in the product?

Answer 2

Lighter isotopes, as they have weaker bonds that are easier to break

Question 3

What does a positive ratio of comparison mean?

Answer 3

A sample is enriched, or heavier than the standard

Question 4

What does a negative ratio of comparison mean?

Answer 4

A sample is depleted, or lighter than the standard

Question 5

How is the hydrological cycle isotopically monitored?

Answer 5

Through stable O and H isotopes in relation to VSMOW measured from seawater and precipitation, as condensation and precipitation correspond to isotopic fractionation

Question 6

Which isotope preferentially occurs as gas?

Answer 6

Lighter isotopes, as their bonds are weaker to break and bump up an energy level into a gaseous state

Question 7

Which isotope preferentially occurs as a liquid or solid?

Answer 7

Heavier isotopes, as their bonds are stronger and harder to break and bump up an energy level into a higher energy state

Question 8

Where does Rayleigh Fractionation occur?

Answer 8

Deserts, evaporative lakes, and polar environments

Question 9

What is the relationship between δ2H SMOW and δ18O SMOW and how is it used?

Answer 9

Linear, so it is used to determine H isotope value for a given O data point

Question 10

How do polar O records indicate global temperature?

Answer 10

Precipitation sets in earlier in colder climates, depleting snow clouds of heavy water and leaving behind less of the heavier isotopes to fall in the poles than in warmer climates, creating an increase in 16O

Question 11

How do isotope records indicate glacial periods?

Answer 11

Oceans become richer in heavier isotopes during glacial periods, as lighter water is trapped in the glaciers

Question 12

What is a potential cause of Dansgaard-Oeschenger periods?

Answer 12

Changing circulation patterns of the Northern Atlantic Ocean through the bipolar seesaw

Question 13

What conditions affect the CCD?

Answer 13

Water temperature, depth, CO2 content, pH, carbonate supply, and terrigenous sediment supply

Question 14

Why are colder marine zones limited in productivity

Answer 14

They lack nitrogen, iron, and phosphorous

Question 15

What are planktic forams used for and why?

Answer 15

Dating rocks, as they are more susceptible to changes in the upper water column and display highly variable temperatures

Question 16

What are benthic forams used for and why?

Answer 16

Analysing long-term environmental change, as they live in stable, constant environments and are sessile, recording ice volume effects while remaining unaffected by regional and climatic changes

Question 17

What conditions affect the δ18O preserved in foraminifera?

Answer 17

Diagenesis, light cycles, water composition, and growth rate, which relate back to the ice volume effect and salinity

Question 18

How are conodonts used to track sea levels?

Answer 18

The changes in composition of carbonate fluoropatite in their phosphatic teeth resulting from diagenetic processes while preserved in the bio-stratigraphic record seawater signals

Question 19

What factors control large scale carbon cycles?

Answer 19

Volcanism, tectonics, fossil fuel burning, and deforestation

Question 20

What are the most common carbon sink processes?

Answer 20

Photosynthesis, rock weathering, carbonate deposition, and ocean adsorption

Question 21

How do paleosols form a climate proxy?

Answer 21

Oxygen isotopes represent geochemical atmospheric conditions, while carbonate nodules mark movement of the water table

Question 22

How is carbon fractionation in alkenones representative of dissolved CO2?

Answer 22

Algal cells allow CO2 to enter in aqueous form, preferentially accepting lighter isotopes to form a lighter composition when dissolved CO2 is high

Question 23

What types of marine organisms can be used to determine atmospheric CO2

Answer 23

Planktic forams and nanofossils, as only the sea surface experiences exchange between aqueous and atmospheric CO2

Question 24

How is the stomatal index used to predict CO2 present in fossils?

Answer 24

The number of stomata increases when CO2 is low to help with the capture of carbon

Question 25

How are Boron isotopes used to predict seawater acidity?

Answer 25

Boron isotopes in forams exhibit pH-based Rayleigh fractionation, with boric acid concentration increasing with acidity

Question 26

What is the carbon isotopic composition in the biosphere, atmosphere, and fossil fuels?

Answer 26

Biosphere: δ13C ~ -29 to -12‰; atmosphere: δ13C ~ -8.4‰ (~ -6.6‰ pre-IR); fossil fuels: ~ -44 to -19‰

Question 27

What are the largest carbon reservoirs?

Answer 27

The ocean, soils, permafrost, and (in the past) the mantle

Question 28

What is the carbon isotopic composition in the ocean?

Answer 28

δ13C ~ -0.6 to 2‰

Question 29

What is the typical process of terrestrial photosynthesis?

Answer 29

Organic matter falls down, decays or burns, then returns to photosynthetic CO2, which is taken up by new plants. Burial or erosion of some of this new organic carbon releases CO2 back to the atmosphere

Question 30

What is the typical process of oceanic photosynthesis?

Answer 30

Upwelling of nutrients drives photosynthesis and organic matter sinks, with CO2 eventually returning to the upper cycle. Burial and subduction of some of this material will eventually release CO2 back into the system

Question 31

What are the ideal conditions for C3 and C4 plants?

Answer 31

C3: cool, dry climates with low daytime growing season temperatures; C4: hot, dry climates with long growing seasons and lots of light

Question 32

What are the carbon isotopic compositions of C3 and C4 plants?

Answer 32

C3: ~ -20 to -26‰; C4: ~ -6 to -16‰

Question 33

What plants belong to the C3 and C4 groups?

Answer 33

C3: flowering plants, trees, shrubs, cereals; C4: grasses

Question 34

How are years of higher precipitation reflected in the tree record?

Answer 34

Thicker rings

Question 35

How do HO, C, and N enter trees?

Answer 35

HO: precipitation, groundwater, and transpiration; C: CO2 storage; N: nitrates and ammonia adsorbed by the roots

Question 36

What processes involve oxygen fractionation in trees?

Answer 36

Water uptake and the production of sugars and cellulose