Lec 7 - Greenhouse Gases and Ice Flashcards
What two important GHGs are found in ice cores?
methane and carbon dioxide
What rhythm is matched by fluctuations in CO2?
the 100ky rhythm of ice sheets
How does CO2 interact with ice sheets?
- driver of changes
- feedback of changes
- combo of driver and feedback to ice sheets
How do ice sheets form?
As snow accumulates, fluffy layers are compressed until ice crystals form, stopping airflow and making a solid sheet
What are the features of the Cryosphere?
- low specific heat
- high albedo
- limited moisture/texture
- polar distribution, highly seasonal
What is the albedo of the Cryosphere?
0.6-0.9
What is the ice-albedo feedback?
planet warms = ice melts, exposing underlying material = lower surface albedo = more light absorbed at surface = more warming
What are 2 climatic effects of sea ice?
- cuts of heat flux from warm ocean and cold Arctic atmosphere
- in summer, melting ice keeps the surface water cool
What are some traits of the hydrosphere relevant to climate?
- low albedo
- large heat capacity
- limited roughness
- high moisture
- 70% of surface
What is the structure of the ocean?
- mixed layer at surface (0-50m)
- deep ocean - colder with depth, less mixing
How can we learn about HOW Carbon has been moved around in the past
isotope ratios! Different pathways use different isotopes
What forms of Carbon can we track?
- organic and inorganic
- ratios of 12C and d13C
What Carbon isotope do plants prefer?
C12 (rather than C13)
How do we know that CO2 is related to ice sheets?
comparing to climate archives !
ice cores and marine 18O records
During glaciation, where does all the atmospheric carbon go?
Carbon reservoirs and transfer!
- Deep ocean!
During interglaciations, what types of C and O are common in the oceans vs land?
oceans have less 18O, more 13C
During glaciations, what types of C and O are common in the ocean?
high 18O, low 13C
In what 3 ways does Carbon get into the deep ocean during glaciation?
- changes to solubility with temperature (cold water = bigger C reservoir capacity)
- Biological transfer (carbon pump – more photosynthesis = more downward movement of C)
- changes in deep water circulation
What is the biological transfer of Carbon into the oceans (carbon Pump)?
plankton photosynthesizing and dying = trapping Carbon in deep ocean
- if organic carbon is oxidised in the ocean into gas again, it can be upwelled
How do changes in deep water circulation affect C reservoirs during glaciation?
- controls how deep carbon can be pumped into the ocean
- water during last glacial max didn’t go as deep as it does today
What was the last glacial max like?
- 21kya
- ice sheets 2km high over NA
- global sea level 110-125m lower
- icy, cold, dry
- more southern tundra systems
What 3 ice sheets covered NA 21kya?
- Cordilleran
- Laurentide
- Greenland
What evidence do we have for the most recent glaciation?
- Global Climate Models
- Geologic evidence (bedrock rebound)
- sediment records (sediment size, glacial dirt)
- pollen (climatic preferences)
What do sediment records tell us about the most recent glacial max?
- evidence of glaciers due to formation left behind (moraines, eskers, silt, boulders)
- sediment records carried by wind (more fine dust than interglacial layers!)
What are some examples of pollen habitat preferences?
- prairie grasses/herbs prefer dry, open areas
- spruce pollen is more abundant in cool/north areas compared to oak
What regions were most drastically affected by glaciation?
- areas closest to ice
- ex North Atlantic (colder, more icce)
- American Pacific Northwest was cooler and drier, but Southwest was wetter due to jetstream placement
What are jet streams?
relatively narrow bands of strong wind in the atmosphere
- blows west to east
- follows parallel to temperature boundary
During the last glacial max, what were areas far from ice sheets like?
- cooler temperatures (even if no ice)
- drier
- lower sea level
- tropics cooler to unknown extent
Why don’t we know how much cooler the tropics were during the last glacial max?
- too far from ice sheets to be affected by ice
- BUT same insolation as today!
- GHGs would have caused the cooling, but unclear how much
