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Dynamic Earth > Past Climate > Flashcards

Past Climate Flashcards

1
Q

What is the difference between climate and weather?

A

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

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2
Q

What are the components of climate?

A
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3
Q

What is the greenhouse effect?

A
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4
Q

What is a feedback?

A

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

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5
Q

What is an albedo?

A

percentage of incoming radiation that is reflected rather than absorbed

High albedo = lots of reflection

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6
Q

What is the feedback effect of water vapour?

A

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

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7
Q

What is the feedback effect of vegetation?

A

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

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8
Q

How does climate cooling affect vegetation?

A

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

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9
Q

What is a climate archive and what are the main types?

A

Record of past climate

loess, marine and ice

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10
Q

What is the resolution of the main archives?

A

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

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11
Q

What kind of proxies do we use?

A

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

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12
Q

How do we use biotic proxies?

A

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

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13
Q

How do we use geological / geochemical data?

A

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)

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14
Q

How do we use ice cores?

A

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

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15
Q

How do we use cave deposits and Lake deposits?

A

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

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16
Q

How do we use trees?

A

Amount of celluose deposited chenges in temperate climates

Precipitation during rainy seasons in dry regions and changes in summer T in cold regions

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17
Q

How do we use corals?

A

O isotopes: seasonal T and precipitations

C isotopes

looking at the bleaching events

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18
Q

What is the difference in amount of radiation Earth and Venus receive?

A

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

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19
Q

What is the Faint Young Sun Paradox?

A

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

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20
Q

How does the faint young sun paradox affect the view of earth’s history?

A

Something must have been keeping earth warm - not working as actuvly any more

Earth’s thermostat - temperature regulator - Greenhouse gases - exchange between resevoirs?

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21
Q

What are the main carbon resevoirs?

A

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

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22
Q

What are some examples of chemical weathering?

A

Weathering on land: silicate bedrock, carbonic acid in solids

Transport in rivers: Ions dissolved in river water

Deposition in ocean - shells of ocean plankton

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23
Q

How does Temperature, precipitation and vegetation affect weathering?

A

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

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24
Q

How can chemical weathering affect negative feedback?

A

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

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25
Q

How would the faint young sun paradox affect weathering?

A

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

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26
Q

What evidence is there for life being the thermostat?

A

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

27
Q

What do we know about the last 550 million years?

A

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

28
Q

What is the polar position hypothesis?

A

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

29
Q

What are two of the super continents and when were there no glaciations?

A

Gondwana and Pangea

No glaciations between 425 and 325 Ma

30
Q

What was the pangea climate like?

A

No evidence of ice sheets

Palmlike vegetation at 40° latitude

Evaporite deposits - continental aridity

Warm summers - limit to glacial growth

31
Q

What does the pangean climate require and whta are the hypotheses for why [CO2] has changed?

A

Reguire 1650 pp [CO2]

2 hypotheses = BLAG and uplift weathering

32
Q

What is the BLAG hypothesis?

A

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

33
Q

What is the uplift weathering hypothesis?

A

Chemical weathering is driver

Uplift caused by:

subduction: relatively constant through time

Continental collision: changes

Does uit also act as a thermostat

34
Q

How would uplift weathering affect climate?

A

Mean rate of weathering affected by availability of fresh rock and mineral surfaces

35
Q

What was the greenhouse world?At aro

A

At around 100 Ma

@ 175 Ma - Pangea begins to break up

@ 100 Ma - separate smaller continents and flooding

36
Q

What was the Greenhouse world like?

A

No ice, even in Antarctica

Unusual warmth - coral reefs @ 40° rather than 30° now

The data model mismatch: Ocean transport hypothesis

37
Q

What is the ocean transport hypothesis?

A
38
Q

What are examples of extreme climate change?

A

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

39
Q

How has the climate changed in the last 55Ma?

A

Profound cooling

40
Q

How is sediment accumulated?

A

Deep sea = few mm per ka

Continental and upwellng - 1-10 cm per ka

Packing is key to speed - 100-200 m oer day

41
Q

How do we use oxygen isotope analysis?

A

Foraminifera incorporate different proportions of 16O and 18O into shells according to temp of sea water

Higer 18:16 ratio = colder

42
Q

How does the sea water change during interglacial and glacial periods?

A
43
Q

HOw have hypothese been tested over the last 55 Ma

A

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

44
Q

What do changing continental configurations affect?

A

Wind and current patterns - inter ocean exchanges on heat and salt

45
Q

What have been key events in the continent configurations?

A

Closing gap betwene central and south america

isolating antarctica

Shutting down equatorial circulation to pacific

46
Q

What is the last few 100,000 years characterised by in terms of climate?

A

Big swings between warm and cold generally every 41,000 years

47
Q

What is eccentricity?

A

How the orbit of the earth changes over time - changes opredictabily between a more oval orbit and more circular

48
Q

What is tilt or obliquity?

A

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

49
Q

What is precession?

A

Change is direction of tilt

Impacts amount of sunlight each hemisphere gets

50
Q

What is important in ice sheet build up?

A

Accumilation and ablation

Ice sheet builds up if accumilation is greater than ablation

51
Q

Which temperature factor is most important in ice sheet build up?

A

Summer temperature - Milankovitch discovered

Low summer insolation is greater ice sheet build up

52
Q

What feedback effects affect ice sheets?

A

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

53
Q

What is the MIS?

A

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

54
Q

How do coral reefs back up MIS evidence?

A

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

55
Q

Wgat information do the coral reefs give us?

A

Uranium datimng allows us to date the reefs

Isotope analysis gives information on isotpic make up of the water

56
Q

Do cave deposits agree with MIS?

A

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

57
Q

What inormation is gathered from ans what is required for 18O analysis?

A

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

58
Q

Any other difficulties witht he speleotherm (cave) record?

A

Speleotherms have to be forming for mean annual temperature to be calculated

In cold times when no speleotherms form you cannot calculate temp

59
Q

How do ice cores give direct measurements of gas?

A

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

60
Q

What are the possible methods of taking up CO2 to move into a glacial period?

A

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

61
Q

How does increased ocean uptake of CO2 affect ocean chemistry?

A

Increase in acidity

High levels of CO2 in the Atlantic due to Atlantic deep water

62
Q

Why does increased CO2 cause greater acidity?

A

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

63
Q
A

Dynamic Earth (4 decks)

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