Term 1 Isotopes & Climate Questions Flashcards
learn the concepts
How does isotope weight impact energy gain?
Heavier molecules have stronger bonds and are harder to bump up in energy level
Which isotope is preferentially used in reactions, and therefore more common in the product?
Lighter isotopes, as they have weaker bonds that are easier to break
What does a positive ratio of comparison mean?
A sample is enriched, or heavier than the standard
What does a negative ratio of comparison mean?
A sample is depleted, or lighter than the standard
How is the hydrological cycle isotopically monitored?
Through stable O and H isotopes in relation to VSMOW measured from seawater and precipitation, as condensation and precipitation correspond to isotopic fractionation
Which isotope preferentially occurs as gas?
Lighter isotopes, as their bonds are weaker to break and bump up an energy level into a gaseous state
Which isotope preferentially occurs as a liquid or solid?
Heavier isotopes, as their bonds are stronger and harder to break and bump up an energy level into a higher energy state
Where does Rayleigh Fractionation occur?
Deserts, evaporative lakes, and polar environments
What is the relationship between δ2H SMOW and δ18O SMOW and how is it used?
Linear, so it is used to determine H isotope value for a given O data point
How do polar O records indicate global temperature?
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
How do isotope records indicate glacial periods?
Oceans become richer in heavier isotopes during glacial periods, as lighter water is trapped in the glaciers
What is a potential cause of Dansgaard-Oeschenger periods?
Changing circulation patterns of the Northern Atlantic Ocean through the bipolar seesaw
What conditions affect the CCD?
Water temperature, depth, CO2 content, pH, carbonate supply, and terrigenous sediment supply
Why are colder marine zones limited in productivity
They lack nitrogen, iron, and phosphorous
What are planktic forams used for and why?
Dating rocks, as they are more susceptible to changes in the upper water column and display highly variable temperatures
What are benthic forams used for and why?
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
What conditions affect the δ18O preserved in foraminifera?
Diagenesis, light cycles, water composition, and growth rate, which relate back to the ice volume effect and salinity
How are conodonts used to track sea levels?
The changes in composition of carbonate fluoropatite in their phosphatic teeth resulting from diagenetic processes while preserved in the bio-stratigraphic record seawater signals
What factors control large scale carbon cycles?
Volcanism, tectonics, fossil fuel burning, and deforestation
What are the most common carbon sink processes?
Photosynthesis, rock weathering, carbonate deposition, and ocean adsorption
How do paleosols form a climate proxy?
Oxygen isotopes represent geochemical atmospheric conditions, while carbonate nodules mark movement of the water table
How is carbon fractionation in alkenones representative of dissolved CO2?
Algal cells allow CO2 to enter in aqueous form, preferentially accepting lighter isotopes to form a lighter composition when dissolved CO2 is high
What types of marine organisms can be used to determine atmospheric CO2
Planktic forams and nanofossils, as only the sea surface experiences exchange between aqueous and atmospheric CO2
How is the stomatal index used to predict CO2 present in fossils?
The number of stomata increases when CO2 is low to help with the capture of carbon
How are Boron isotopes used to predict seawater acidity?
Boron isotopes in forams exhibit pH-based Rayleigh fractionation, with boric acid concentration increasing with acidity
What is the carbon isotopic composition in the biosphere, atmosphere, and fossil fuels?
Biosphere: δ13C ~ -29 to -12‰; atmosphere: δ13C ~ -8.4‰ (~ -6.6‰ pre-IR); fossil fuels: ~ -44 to -19‰
What are the largest carbon reservoirs?
The ocean, soils, permafrost, and (in the past) the mantle
What is the carbon isotopic composition in the ocean?
δ13C ~ -0.6 to 2‰
What is the typical process of terrestrial photosynthesis?
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
What is the typical process of oceanic photosynthesis?
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
What are the ideal conditions for C3 and C4 plants?
C3: cool, dry climates with low daytime growing season temperatures; C4: hot, dry climates with long growing seasons and lots of light
What are the carbon isotopic compositions of C3 and C4 plants?
C3: ~ -20 to -26‰; C4: ~ -6 to -16‰
What plants belong to the C3 and C4 groups?
C3: flowering plants, trees, shrubs, cereals; C4: grasses
How are years of higher precipitation reflected in the tree record?
Thicker rings
How do HO, C, and N enter trees?
HO: precipitation, groundwater, and transpiration; C: CO2 storage; N: nitrates and ammonia adsorbed by the roots
What processes involve oxygen fractionation in trees?
Water uptake and the production of sugars and cellulose
