Past Climate Flashcards
What is the difference between climate and weather?
Climate is what you expect weather is what you get
Climate: broad composite of average condition of a region - long term greater than years
Weather: shorter fluctuations - Temp, precip, ice cover, winds (minutes months)
Climate change: changes in long terms averages of weather
What are the components of climate?
What is the greenhouse effect?
What is a feedback?
There is an initial climate forcing event which causes an initial climate response which is then amplified over time in a positive system and reduced over time in a negative system
What is an albedo?
percentage of incoming radiation that is reflected rather than absorbed
High albedo = lots of reflection
What is the feedback effect of water vapour?
Initial change leads to climate warming
Means greater evaporation and air contains more water vapour
Water vapour is greenhouse gas so increased trapping of radiation
Not considered as a climate forcer as it changes as a function of temp
What is the feedback effect of vegetation?
Initial change causes increasesd precipitation
This causes greater growth of trees so forests replace grasslands
Trees have greater transpiration than grasses which leads to more water in the atmosphere and greater precipitation
How does climate cooling affect vegetation?
Initial effect is causes climate cooling
forest replaced by cooler climate begetation
Allows more snow to settle on it = high albedo
Leads to greater cooling
What is a climate archive and what are the main types?
Record of past climate
loess, marine and ice
What is the resolution of the main archives?
Sediment - low energy
metres per year - m a-1 in coastal marine sequences
mm a-1 in lakes
mm ka-1 in deep-sea sediment - no seasonal records
Ice cores - annual leyers initially <10ka
Tree rings, coral, speleotherms = annual
What kind of proxies do we use?
Proxy = substitute
Biotic proxy = changing composition of plant and animal groups
Geological - geochemical proxies
- quantify mass movements of Earth’s materials through the climate system
either as discrete (physial) particles or in dissolved (chemical) form
How do we use biotic proxies?
Cocoliths, pollen fossils
Look at the climate preferences of living species from presen-day distribution
Past climate inferred from fossil assemblages
e.g - look at pollen to sea which species were living in a certain area
How do we use geological / geochemical data?
Mass movement tied to processes of erosion, transport and deposition
Striation, ice wedge cast
Ocean sediments
Isotopic fractionation: Sr (river fluxes + fluid exchange), O (ice volume and T), C (organic material movements / circulation)
How do we use ice cores?
Air bubbles contain CO2 and CH4
The thickness of snow deposits gives info on T and moisture contanet
Dust - chemical signatures from redional sclae sources
Sea salt
How do we use cave deposits and Lake deposits?
Cave: records of ground water over ka
Chemical composition - original source of water vapour, atmospheric transport path to site of precipitation, ground water environment
Lake: fluctuatiuons of lake level, chemical tracers
How do we use trees?
Amount of celluose deposited chenges in temperate climates
Precipitation during rainy seasons in dry regions and changes in summer T in cold regions
How do we use corals?
O isotopes: seasonal T and precipitations
C isotopes
looking at the bleaching events
What is the difference in amount of radiation Earth and Venus receive?
Venus receives 2 x solar radiation but dense su;lfuris acid cloud cover reflects 80%
Venus and Earth have similar amount of carbon but venus’ CO2 - rich atmosphere creates a stringer greenhouse effect
What is the Faint Young Sun Paradox?
Earliest sun shone 25-30% more faintly thatn today
If so the Earth would have been frozen for first 2-3 Ga
But there is prevelence of sedimentary rocks and running water
1st evidence of ice deposits in sediments is 2.3 Ga btu probably polar
Life dates back to 3.5 Ga
How does the faint young sun paradox affect the view of earth’s history?
Something must have been keeping earth warm - not working as actuvly any more
Earth’s thermostat - temperature regulator - Greenhouse gases - exchange between resevoirs?
What are the main carbon resevoirs?
Volcanic input of C fri rocks to atmosphere - thought not to react in this way - too divorced from the atmosphere
Removak of CO2 from the atmosphere by chwmical weathering - are rates sensitive ti climate, T, precipitation and vegetation
What are some examples of chemical weathering?
Weathering on land: silicate bedrock, carbonic acid in solids
Transport in rivers: Ions dissolved in river water
Deposition in ocean - shells of ocean plankton
How does Temperature, precipitation and vegetation affect weathering?
Temp: silicate weathering rates double for each increase of 10 degrees
Precipitation: combines with CO2 to form carbonic acid
Vegetation: extract CO2 from air to soils, this is increased at higher temp
How can chemical weathering affect negative feedback?
Initial change, warmer climate, increased temp, precip, vegetation, incrased chemical weathering, increased removal of CO2, reduction if warming
Initial change, colder climate, decreased temp, precip, vegetation, decreased chemical weathering, decreased removal of CO2, reduction of cooling
How would the faint young sun paradox affect weathering?
Early erath - more act8ive vulcanism and bombardment
Less continental area, slower weathering
As sun strengthens, surface warms, chemical weathering increases, drop in atmospheric CO2
Also outgassing of CH4 and NH3 but these are broken down quickly
What evidence is there for life being the thermostat?
Gaia hypothesis: life regulating climate
Several features of chemical weathering directly involve action of life forms
But CaCO3 shells only at 540 Ma
Life could be too primitive to chanf=ge climate
Oxidised Fe at 2.3 Ga - marine photosynthesis
Biological evolution matches need for greater chemical weathering
What do we know about the last 550 million years?
Location of containents
well preserved sedimentary rock archive
Little over printing
For the last 175Ma can measure sea floor spreading rates + establish latitude and longitude
What is the polar position hypothesis?
Ice sheets should appear on continents when they are located at polar / near polar latitudes
No iceis no continents near poles
THis explains icehouse worlds with just continental movement
Low angles of incident solar radiation
High albedos from snow and ice
What are two of the super continents and when were there no glaciations?
Gondwana and Pangea
No glaciations between 425 and 325 Ma
What was the pangea climate like?
No evidence of ice sheets
Palmlike vegetation at 40° latitude
Evaporite deposits - continental aridity
Warm summers - limit to glacial growth
What does the pangean climate require and whta are the hypotheses for why [CO2] has changed?
Reguire 1650 pp [CO2]
2 hypotheses = BLAG and uplift weathering
What is the BLAG hypothesis?
Climate change in last 500 Ma driven mainly by changes in CO2 input by plate techtonics: Berner, Lasaga and GArrels
Vhanges in rate of seafloor spreading over MA control rate of delivery of CO2 from rock resevoir - Driver
Faster spreading = more ocean crust = more releases of magma
Chemica qeathering moderates by negative feedback
What is the uplift weathering hypothesis?
Chemical weathering is driver
Uplift caused by:
subduction: relatively constant through time
Continental collision: changes
Does uit also act as a thermostat
How would uplift weathering affect climate?
Mean rate of weathering affected by availability of fresh rock and mineral surfaces
What was the greenhouse world?At aro
At around 100 Ma
@ 175 Ma - Pangea begins to break up
@ 100 Ma - separate smaller continents and flooding
What was the Greenhouse world like?
No ice, even in Antarctica
Unusual warmth - coral reefs @ 40° rather than 30° now
The data model mismatch: Ocean transport hypothesis
What is the ocean transport hypothesis?
What are examples of extreme climate change?
K-T event: - 65 Ma - global extinction of 70& of species,
Ir-rich layer asteroid impact, Stratopheric partiles block out light = cooling, Abrupt injection of C biomass - higher CO2
Paleocene-Eocene thermal maximum - Global T increase @ 55 Ma of 6 degrees celcius of 20ka, Excursion in carbon 13 methane hydrates
Carbonate dissolution
How has the climate changed in the last 55Ma?
Profound cooling
How is sediment accumulated?
Deep sea = few mm per ka
Continental and upwellng - 1-10 cm per ka
Packing is key to speed - 100-200 m oer day
How do we use oxygen isotope analysis?
Foraminifera incorporate different proportions of 16O and 18O into shells according to temp of sea water
Higer 18:16 ratio = colder
How does the sea water change during interglacial and glacial periods?
HOw have hypothese been tested over the last 55 Ma
BLAg: slow > 15 Ma - fits
increased since <15 Ma - should hagve put more CO2 into atmosphere and warmed climate more
Uplift weathering - largest plateau for 250 Ma
What do changing continental configurations affect?
Wind and current patterns - inter ocean exchanges on heat and salt
What have been key events in the continent configurations?
Closing gap betwene central and south america
isolating antarctica
Shutting down equatorial circulation to pacific
What is the last few 100,000 years characterised by in terms of climate?
Big swings between warm and cold generally every 41,000 years
What is eccentricity?
How the orbit of the earth changes over time - changes opredictabily between a more oval orbit and more circular
What is tilt or obliquity?
How the angle of the tilt changes
Tilt leads to seasons
Angle of tilt changes how big seasonal change is over tiem
41,000 year timescale
What is precession?
Change is direction of tilt
Impacts amount of sunlight each hemisphere gets
What is important in ice sheet build up?
Accumilation and ablation
Ice sheet builds up if accumilation is greater than ablation
Which temperature factor is most important in ice sheet build up?
Summer temperature - Milankovitch discovered
Low summer insolation is greater ice sheet build up
What feedback effects affect ice sheets?
No ice sheet in an interg;lacial period
Low summer insolation, ice sheet grows, when at minimum ice sheet grows fast, bedrock depression is delayed, ice sheet stays at high altitudes and grows faster
Eventually bedrock depresses
When high summer insolation, icesheet melts, bedrock rebound delayed for thousands of years, icesheet stays low, warmer elevations, ice melts faster
What is the MIS?
The marine oxygen isotope stages
evidence for glacial and interglacial periods using the marine sediment record of Planktonic (SST and Ice) and Benthic (ice volume)
Shows clear link between levels of CO2 and changes in temp
around 280 ppm in warm periods and 180 ppm in cold
How do coral reefs back up MIS evidence?
When building up ice sheet sea levels start to reduce
When melting ice sheets sea levels increase.
Coral reefs build p at the sea level - can see old coral reefs at previous sea levels - observe sea leels rising and falling with glacial and intergalcial periods
Wgat information do the coral reefs give us?
Uranium datimng allows us to date the reefs
Isotope analysis gives information on isotpic make up of the water
Do cave deposits agree with MIS?
Cavel stalagtites can be dates with uranium and doing isotope analysis on them
When warm you get stalagtite production and not when its cold
Stalagtite formation from degassing of CO2 and supersaturation of CaCO3 and precipitation
What inormation is gathered from ans what is required for 18O analysis?
If T of deep caves is in equilibrium with mean anual temperature uou can make direct paleotemperature estimation using 18O in carbonate or of the water
Carbonate precipotation must be in isotopic equilibrium
delta 18O of water must be known
no diagenetiuc alteration
no detrital contamination
Any other difficulties witht he speleotherm (cave) record?
Speleotherms have to be forming for mean annual temperature to be calculated
In cold times when no speleotherms form you cannot calculate temp
How do ice cores give direct measurements of gas?
Snow on the top of ice is fluffy and has good air flow
As more snow falls is packs more together and crystals start to form
For a while air can still diffuse through the ice slowly but at a certain point the air bubbles become sealed (process called sintering)
The average age of the air is younger than ice
What are the possible methods of taking up CO2 to move into a glacial period?
Ocean temp drops = more ability to take up CO2
More water in glacias = greater salinity = less ability to take up CO2
Tropical upwelling regions = take up of CO2
Biogeochemical redistribution = take up of CO2
How does increased ocean uptake of CO2 affect ocean chemistry?
Increase in acidity
High levels of CO2 in the Atlantic due to Atlantic deep water
Why does increased CO2 cause greater acidity?
Increased partial pressure of CO2 causes the ocean to take up more CO2
The equilibrium is pushed towards teh formation of bicarbonate which releases H+ ions
