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LPC 2020 S2 - EAE1012 - Earth Science 2 > EAE 13 - Climate proxies > Flashcards

EAE 13 - Climate proxies Flashcards

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Biology 101 flashcards
1
Q

What does palaeoclimate science try to do?

4 points.

A
  • Identify the nature of past climate changes
  • Synthesize a coherent, falsifiable narrative describing major palaeoclimate events
  • Understand the dynamics shaping these events
  • Inform the evaluation and development of climate models

EAE 16aa

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2
Q

What is Palaeoclimatology at the Tectonic-scale?

4 points.

A
  • Chemical weathering is an atmospheric CO₂ sink and its variation over time is a hypothesised long-term thermostat of the Earth
  • Plate tectonics have large impact on topography and ocean/atmosphere circulation
  • Distribution of sensible/latent heat
  • Solid Earth is a huge carbon reservoir but slow exchange rate
  • Immense changes have occurred in the past: e.g.
    • 5 mass extinctions
    • Snowball and Greenhouse Earth
    • Closure of Tethys sea 50 Ma
    • Opening of Drake’s passage (25 Ma)
    • Global cooling

EAE 16ab

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3
Q

What are the main pieces of evidence for ice sheet
history?

2 points.

A
  • Foraminifera δ¹⁸O indicate ice volume and ocean temperature
  • Ice-rafted debris: sediments from melting icebergs calved from ice-sheet margins

EAE 16ac

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4
Q

What is the quaternary glaciation activity over last 2.75Ma?

5 points.

A
  • Slow drift towards more ice, change in glaciation threshold
  • δ¹⁸O lags behind orbital changes to summer insolation
  • Change from 41,000 to 100,000 yr cycles (see Huybers, 2007)
  • ~Fifty glacial maxima!
  • Slow trend part of 50My trend

EAE 16ad

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5
Q

What are the orbital-scale change cycles?

3 points.

A

Three key orbital cycles

  • Eccentricity
  • Obliquity
  • Precession

Change the distribution of incoming solar radiation

EAE 16ae

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6
Q

What are the cycles of the orbital scale changes?

3 points.

A

Periodic cycles:

  • ~100-400 ky
  • 41 ky
  • 23 ky

EAE 16af

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7
Q

What are the effects of orbital scale changes?

7 points.

A
  • Ice sheet extent
  • Atmospheric greenhouse gases
  • Sea level (~120m lower!)
  • Monsoons
  • Circulation
  • Vegetation
  • Global temperature

EAE 16ag

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8
Q

What other things influce orbital scale changes?

2 points.

A
  • Immense ice sheets affect global climate
  • Positive and negative feedbacks (e.g. icealbedo), delays (e.g. bedrock), nonlinearities (e.g. accumulation / melt)

EAE 16ah

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9
Q

What was the climate at Last Glacial Maximum?

3 points.

A

LGM at 21-26 ka

  • ~4-7°C colder
  • Sea level 110-125m lower
  • Ice sheets ~2-3km thick

EAE 16ai

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10
Q

What has been the climate since LGM?

4 points.

A
  • Summer insolation at 10 ka was at a maximum (Obliquity and Precession), drives ice sheet melt, GHG rise and further melting due to ice-albedo effect
  • Brief interruptions to warming (Younger Dryas 13 ka, Antarctic Cold Reversal 14 ka)
  • Millennial Oscillations: non-cyclical, high amp Nhem, ice sheet instability, thermohaline and atmos circ.
  • Pleistocene (2.6 Ma to 12 ka) epoch of glacial-interglacials ended, gave way to stable, warm Holocene

EAE 16aj

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11
Q

What is a positive feedback loop?

4 points.

A
  1. Initial climate forcing action
  2. Intial climate response
  3. Response amplified by climate system
  4. Response becomes new input (i.e. Goes back into 1).

EAE 16ak

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12
Q

What does the symbol ‘‰’ mean?

A

‰ is “per mil” i.e. per thousand

Just as % is “per cent” i.e. per hundred

EAE 16al

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13
Q

What is δ¹⁸O?

A

δ¹⁸O is a measure of the departure from a standard reference ratio of ¹⁸O/¹⁶O

EAE 16am

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14
Q

What are typical values for δ¹⁸O?

3 points.

A
  • Surface tropics 0 to -2‰
  • Deep ocean +3 to +4‰
  • Polar Ice -30 to -55‰

EAE 16an

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15
Q

5 points.

A
  • Fractionation of the isotopes relate mostly to temperature of ocean water
  • Lighter ¹⁶O evaporates preferentially
  • Heavier ¹⁸O condenses to precipitation preferentially
  • Atmospheric circulation transports water vapour towards poles
  • For a ~4°C increase in temperature, δ¹⁸O reduces by about 1‰

EAE 16ao

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16
Q

What is the δ¹⁸O in seawater?

A

In seawater δ¹⁸O ∝ Temperature of seawater

Planktic forams (upper 100m)

Benthic forams (sea floor)

EAE 16ap

17
Q

What is a ‘foram’?

A

Foraminifera

From Wikipedia:

Single-celled organisms characterized by streaming granular ectoplasm for catching food and other uses and commonly an external shell (called a “test”) of diverse forms and materials.

Most foraminifera are marine, the majority of which live on or within the seafloor sediment (i.e., are benthic), while a smaller number float in the water column at various depths.

EAE 16aq

18
Q

What is the δ¹⁸O in ice sheets?

A

In ice sheets δ¹⁸O ∝ Temperature of snow

Other factors also impact such as transport, seasonality, elevation

EAE 16ar

19
Q

What is a Speleothem?

A

Speleothems commonly known as cave formations, are secondary mineral deposits formed in a cave. Speleothems typically form in limestone or dolomite solutional caves.

The definition of speleothem, in most publications, specifically excludes secondary mineral deposits in mines, tunnels, and other man-made structures.

From Wikipedia

EAE 16as

20
Q

What is the δ¹⁸O in speleothems?

2 points.

A
  • In speleothems δ¹⁸O ∝ Monsoon strength (precip)
  • ¹⁶O higher when lots of evap/precip

EAE 16at

21
Q

How does the δ¹⁸O change in glacial climates?

3 points.

A

Ice/Marine responses are opposite; In glacial climates:

  • Ice core δ¹⁸O ↓
  • Marine δ¹⁸O ↑

EAE 16au

22
Q

What is obliquity of orbit?

A

Tilt of the poles relative to the plane of orbit?

Note this is true poles (i.e. axis of rotation) not magnetic poles.

EAE 16av

23
Q

What is eccentricity of orbit?

4 points.

A

How elliptical is the orbit?

Distance between Earth and Sun:

  • Orbit is not a perfect circle
  • Due to gravity of other planets
  • Small effect on solar radiation
  • Interval between equinoxes not equal (one is 7 days longer)

EAE 16aw

24
Q

When are the earth’s solstices?

A

~21 Jun/Dec

EAE 16ax

25
Q

When are the earth’s equinoxes?

A

~21 Mar/Sep

EAE 16ay

26
Q

When is the earth’s perihelion?

A

4 July

Perihelion = Nearest point of a body’s direct orbit around the Sun

EAE 16az

27
Q

When is the earth’s Aphelion?

A

3 January

Aphelion = Furthest point of a body’s direct orbit around the Sun

EAE 16ba

28
Q

How does the sunlight vary for the earth?

A

Overall 6% more sunlight reaches Earth at aphelion vs perihelion

EAE 16bb

29
Q

How does obliquity change?

8 points.

A
  • 1,000 year regular cycle
  • Present tilt 23.5°
  • Tilt currently decreasing
  • Small variations in amplitude
  • Range is 22.2° to 24.5°
  • Last max: 8700 BCE
  • Next min: 11,800 CE
  • One of the ‘Milankovitch’ cycles

EAE 16bc

30
Q

What is the effect of obliquity?

2 points.

A
  • Amplify/suppress seasons
  • Biggest impacts at the poles

EAE 16bd

31
Q

What is the earth’s orbital eccentricity?

4 points.

A

How elliptical is the earth’s orbit?

  • Currently 0.0167 (nearer to circular)
  • Ranges between 0.005 and 0.0607
  • Periods of 100,000 yr and 413,000 yr
  • The second of the Milankovitch cycles

EAE 16be

32
Q

What is the precession of the equinoxes?

4 points.

A
  • Wobbling motion
  • Change in the direction of the lean (not the angle itself that’s Obliquity!)
  • Minor and major axes shift slowly in time
  • We can understand precession as a variation in the solstices/equinoxes relative to the perihelion

EAE 16bf

33
Q

What is the precession of the equinoxes?

6 points.

A
  • Axial precession and orbital precession combine to create the precession of the equinoxes
  • The major periodicity is at about 23,000 years
  • In addition to these two effects, eccentricity modulates precession
  • The precessional index represents the overall affect of precession and eccentricity: 𝛆 sin(𝛚)
  • Angle 𝛚 helps simplify equations of motion and is the angle between these the imaginary lines of the perigelion axis and the March 20 equinox
  • This is the third Milankovitch cycle

EAE 16bg

34
Q

What is the Impact of Eccentricity on Precession?

5 points.

A
  • Changes in eccentricity magnify/suppress contrasts
  • Combined effects cause the distance from Earth to Sun to vary by season
  • High eccentricity → highest contrasts in Earth-sun distance
  • Low eccentricity → lowest contrasts in Earth-sun distance
  • Precession influences the seasonality of arriving radiation

EAE 16bh

35
Q

What is solar insolation?

A

Radiation received at the top of atmosphere

EAE 16bi

36
Q

What are the long term changes in insolation?

4 points.

A
  • Orbital changes affect the amount of solar insolation
  • Influence of cycles of precession (P) and tilt (T) vary with latitude
  • Precession: influences insolation at low-mid latitudes, and high latitudes in summer only
  • Obliquity (tilt): influences winter insolation at higher latitudes (60° N/S)

EAE 16bj

37
Q

What would have helped the melting along once orbital cycles kick things off?

3 points.

A
  • Summer insolation: Melting began due to increased summer insolation (obliquity and precession)
  • Greenhouse gases: As ice sheets melted, CO2 and CH4 rose, enhancing the greenhouse effect: Positive Feedback
  • Surface albedo: changed as ice sheets melted: Positive Feedback

EAE 16bk

LPC 2020 S2 - EAE1012 - Earth Science 2 (18 decks)

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