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Physical Geography > Quaternary Glaciation > Flashcards

Quaternary Glaciation Flashcards

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1
Q

What do scientists say about the next ice age?

A
  • As of 2016, scientists believe that the next ice age may have been delayed by human activities which have caused an increase in greenhouse gases in the atmosphere.
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2
Q
  • What is the quaternary period?
A
  • 2.6 million years ago to the present day
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3
Q

What is the Holocene?

A
  • 11.5 thousand years ago until the present day
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4
Q

What might proxy data show?

A
  • Regular and frequent climate fluctuations
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5
Q

How might oxygen isotopes show us climate fluctuations?

A
  • Oxygen isotopes can be found in ocean cores 018/016
  • There have been 100 oxygen isotope stages in the last 2.5Ma
  • Shows glacial and interglacial cycles and changing periodicity over the last 8000 years.
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6
Q

What is the ‘forcing function’?

A
  • The mechanism that causes systems to change from their equilibrium state and is drive by perturbations in the earth-atmosphere system.
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7
Q

Give an example of an external and internal forcing mechanism

A
  • ice sheet growth due to changing solar radiation increases albedo and reduces temps.
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8
Q

Give an example which illustrates the importance of feedbacks and interconnectivity of the climate system

A
  • Reduction in radiative forces causes ice sheet growth changing the earths albedo.
  • Reduces global temperatures causing more ice sheet growth.
  • Positive feedback amplifies changes in the climate system whilst negative feedback counters changes within the system.
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9
Q

What are some examples of external forcing mechanisms in the climate system?

A
  • Solar output and orbital patterns
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10
Q

What are some examples of internal forcing mechanisms in the climate system?

A
  • Feedback by earth’s elements (albedo, ocean currents)
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11
Q

What are the specific spatial and temporal impacts of external and internal forcing functions?

A
  • Different elements respond over different timescales

- Long term climate changes involve progressively more components of the earth-atmosphere system.

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12
Q

How and when did we get into a glacial global climate?

A
  • First evidence of widespread glaciation was that deep ocean cores revealed larger and more persistent volumes of ice-rated debris at c.2.6Ma BP
  • Cores also show increase in volcanic ash from 2.Ma = increased global volcanism
  • SO2 aerosols (increase in earths albedo maybe?
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13
Q

Why did the post Cretaceous inception of Quaternary ice cover occur?

A
  • Raised areas above the regional glaciation limit
  • Modified atmospheric circulation patterns
  • Increased weathering rates resulting in removal of CO2 from the atmosphere.
  • Increased rustiness of atmosphere due to uplift of Tibetan Plateau suggesting increased aridity between 3.6-2.6 Ma
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14
Q

What were the causes of the Pliocene- Pleistocene transition?

A
  • Disposition of land masses and ocean gateways
  • Tectonic activity
  • Feedback mechanisms
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15
Q

Who was Alfred Wegener?

A
  • Theorised continental drift
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16
Q

How did disposition of land masses and ocean gateways cause the Pliocene- Pleistocene transition?

A
  • poleward migration of major land masses
  • isthmus of Panama closing (3-3.5Ma)
  • separation of Antarctica and Australia
  • isolation of Antarctica by 40Ma (Antarctic Ice Sheet stable ever since)
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17
Q

How did tectonic activity cause the Pliocene- Pleistocene transition?

A
  • mountain building (Himalaya/Tibetan plateau = 3000 in 2Ma). This changed the wave structure of air streams in the upper atmosphere and cooled temps in the Northern Hemisphere
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18
Q

How did feedback mechanisms lead to the Pliocene- Pleistocene transition?

A
  • Ocean-atmosphere circulations
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19
Q

What was the climate cycle periodicity during the Pliocene- Pleistocene transition?

A
  • 41,000 years prior to 800ka BP

- 100,000 years after 800ka BP

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20
Q

What happened in the Mid-Pleistocene transition?

A
  • There was an intensification of glaciation since 800ka BP

- Why?

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21
Q

Why was there an intensification of glaciation during the mid-Pleistocene transition?

A

A) Long term reduction in atmospheric CO2- lowering past a critical threshold for large ice sheets to develop in NH
b) Ice sheet thickness and subglacial substrate

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22
Q

Explain how a long term reduction in atmospheric Co2 may have led to an intensification of glaciation during the P-P transition

A
  • Due to tectonic uplift and associated increased weathering rates.
  • Decreased the greenhouse effect and allowed ice sheets to expand into areas that were previously two warm for ice to survive through successive summers.
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23
Q

Explain how ice sheet thickness and subglacial substrate may have led to glaciation intensification during the P-P transition?

A
  • Oxygen isotopes show change in cyclicality but also increase in ice sheet volume at 1Ma ago. Prior to this the NH sheets were equally extensive.
  • To accommodate the volume, they must have been thicker after 1Ma. Thicker ice sheets would have been more likely to survive rapid warming episodes of the 41 ka cycle.
  • Why change in glacial = subglacial substrate
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24
Q

What was the Croll- Milankovitch astronomical theory?

A
  • main premise= changes in intensity of seasons in NH control ice sheet inception and decay
  • NH latitude summer temps key to the onset of glaciation. If cold enough winter snows would not completely melt and would grow into glaciers.
  • Earth’s distance from the sun varies seasonally (perihelion- nearest in NH winter and aphelion- furthest away in NH summer).
  • Uneven receipt of insulation is further accentuated by orbital parameters of eccentricity, obliquity and precession.
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25
Q

What did the Croll-Milankovitch theory say controlled glaciation?

A
  • Glacial/interglacial periods due to cyclical changes in earth’s orbit around the sun.
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26
Q

What did the Croll- Milankovitch theory say about eccentricity?

A
  • 100ka and 400ka

- Change in shape of earths orbit from circular to elliptical =0.03% max change in annual insolation receipt

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27
Q

What did the Croll- Milankovitch theory say about obliquity?

A
  • 41ka
  • Change in tilt of Earth’s axis of rotation from 21.8 to 24.4 degrees
  • Larger differences between seasons as tilt increases
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28
Q

What did the Croll- Milankovitch theory say about precession?

A
  • 23ka and 19ka
  • Wobble of earth on its axis due to gravitational attraction of sun and moon.
  • Alters timing and variability of seasons.
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29
Q

What is a good example of cyclicity in the landscape?

A
  • River terraces
    1) DOWNCUTTING- During cold/warming periods land is downcut
    2) AGGRADATION- During cold/warming periods sediment then collects at the bottom of the valley
    3) INTERGLACIAL- During temperate periods
    4) EROSION- Cooling/cold
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30
Q

Summarise why longer term climate change occurs?

A
  • Multiple components of the earth-atmosphere system change including tectonics, orbital changes and volcanoes.
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31
Q

What doe every element contain?

A
  • A number of protons which give it a unique atomic number
  • e.g. Oxygen = 8
  • Every element also has an umber of neutrons which give it an economic weight BUT this number can vary
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32
Q

Describe oxygen as an element

A
  • Oxygen may have 7,8,9 or 10 neutrons, which when added to the number of protons gives isotopes of mass O15,O16, O17 or O18
  • These isotopes are then heavier or lighter than each other
  • Some may be unstable and don’t exist in nature
  • Others such as O16 and )18 are known as ‘stable’ isotopes and are more consistent.
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33
Q

What effect do oxygen isotopes have in reality?

A
  • Variations in the ratio of O16 and O18 indicate changing isotopic composition of ocean waters between glacials and interglacials
  • These oxygen isotopes ratios in seawater are largely controlled by fluctuations in land-ice volume. Downcore variations record glacial/ interglacial climatic oscillations.
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34
Q

Describe oxygen in glacials

A
  • O16 is evaporated from water earliest. Hence ocean waters are relatively enriched in O18 while ice sheets are more enriched in O16.
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35
Q

Describe oxygen in interglacials

A
  • Melting ice sheets return more O16 to the ocean.
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36
Q

Describe the oxygen isotope records

A
  • Record of glacier ice volume through time from analysis of marine microfossils in ocean floor sediments and ice cores.
  • Glacial = O16 depletion in ocean and enrichment in ice
  • Interglacial- O16 enrichment in ocean and depletion in ice
  • Analysis of marine sediment cores
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37
Q

What are the marine isotope stages?

A
  • Glaciation= O16 preferentially locked up in ice- isotopically heavier ocean water
  • Quaternary climato-stratigraphy = marine isotope stages (MS)
  • Even numbers= cold stages
  • Odd numbers= warm stages
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38
Q

What is the ocean core palaeoclimate record?

A
  • Deep sea record is the longest and best preserved palaeoclimate record: low regular sedimentation rate, negligible erosion
  • ‘Proxy’ data = a) Biogenic sediments formed from the skeletal remains of calcareous organisms (e.g. Microfossils)
  • i) record isotopic balance of the water they inhabited ii) relative abundance iii) morphology/species
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39
Q

Describe ocean cores

A
  • Increases during glaciation and provides a deep-sea record of ice sheet fluctuations.
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40
Q

What can ice cores tell us?

A

1) Temp
2) Gas content of atmosphere
3) Dust (particles). Past aeolian activity and marker horizons
4) Volcanic eruptions (sulphur)
5) Annual layers (dating technique)

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41
Q

How do ice cores tell us about past temps?

A
  • Looking at the different oxygen isotopes for correlation with the marine record
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42
Q

How do ice cores tell about the gas content of the atmosphere?

A
  • CO2, CH4 in bubbles in the ice
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43
Q

How does dust tell us about the past dust particles?

A
  • Past aeolian activity and marker horizons
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44
Q

Describe ice cores and oxygen isotope analysis?

A
  • Glacials= depletion of O16 in ocean water and enrichment in ice and depletion of O18 and deuterium in glacier ice
  • Interglacials= enrichment of O16 in ocean water and depletion in ice and enrichment of O18 and D in glacier ice
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45
Q

Describe ice core records of long-term climate change

A
  • Long-term changes in atmospheric greenhouse gases
  • Correspondence between CO2, CH4 and temp. As gas conc increases so does temp.
  • EPICA core at Dome C (Antarctica)- climate record stretching back to 800,000 years BP
  • Comparison of MIS 11 interglacial with present interglacial (See graph)
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46
Q

What are the different external and internal forcing functions and what are their specific spatial and temporal impacts?

A
  • Different elements respond over different timescales

- Long term climate changes involve progressively more components of the earth-atmosphere system.

47
Q

What is the importance of fine-resolution palaeoclimate records (ice cores)- ‘sub- Milankovitch’ climate change.

A
  • Oxygen isotope signal = that weird looking code
  • High frequency climate oscillations- 20 interstadials of 500-2000 years of relatively mild climate during the last cold stage (80-20ka BP)
  • Dansgarrd- Oeschger events- show gradual cooling followed by an abrupt warming
  • Temperature changes of 7 degrees between warm and cold stages. Abrupt start; more gradual decline.
  • First discovered by Willi Dansgaard in the 1970s and written off as ‘noise’ (now recognised as evidence of climate’s flickering switch).
48
Q

Give an ocean example of earth’s climate system and mechanisms?

A
  • Themohaline circulation= temperature and salinity driven currents- initiated by
    A) Cooling of surface water and increasing of its density
    B) Addition or removal of freshwater (eg iceberg armadas)
    Importance- sensitive to freshwater input (reduces density so hard to sink; if slows down/ stops- massive cooling in N Atlantic region- threshold crossed.
49
Q

What is the importance of fine resolution palaeoclimate records like oceans in deep sea core?

A
  • Six layers of Ice Rafted Debris (IRD) detected in North Atlantic sediment cores- ‘Heinrich layers’
  • Heinrich layers (H1-H6) deposited ~70-14ka BP. Frequency 7-10ka yrs
50
Q

Define Heinrich events

A
  • Marked by layers rich in ice-ranted debris in marine sediment cores, which record massive iceberg discharges (purging ice sheets) with a ~cyclic occurrence which is closely linked to Dansgaard-Oeschger cycles
51
Q

Define Dansgaard-Oeschger cycles

A
  • Rapid climate fluctuations during the last cold stage (~20 in number, with a periodicity between 1000-2000 years (thus sometimes called ‘millennial cycles’
52
Q

What are bond cycles?

A
  • Longer term cooling cycles 10,000-15,000 years long during the last cold stage.
53
Q

Describe ice core/ocean core correlation and fine resolution records

A
  • High frequency climate oscillations - long term cooling cycles and abrupt warming (bond cycles) = climate’s flickering switch
54
Q

What is the most powerful means of palaeoclimate reconstruction?

A
  • Stable isotope analysis of deep sea sediments and ice cores
  • Foundation of knowledge about Quaternary climate change and allow identification of glacial- interglacial cyclists at Milankovitch scales.
55
Q

What are quaternary glacials?

A
  • Large areas of mid to high latitudes of the northern hemisphere were covered by large ice sheets e.g. North America, UK, Switzerland
56
Q

Describe palaeoclimatology or the reconstruction of former ice cores

A

A) Former ice sheets ‘footprint of flow’ (subglacial landform)
B) Former ice sheet margins (moraines, tills, melttrates landforms
C) Former ice sheet thickness (trimlines)
D) Dating (radiocarbon, surface exposure dating)

57
Q

Describe ice flow directional landforms

A
  • Glacier footprint- ice flow directional indication (Flutings, drum lin)
  • From parallel to former ice flow direction
  • Flutes associated with boulders acting as obstacles against glacial flow
58
Q

Describe subglacial landform Drumlins

A
  • Elongated in direction of glacial flow

- Blunt upstream and with a tapered end or tail

59
Q

Name some former glacier margins

A

1) Moraines

2) Trimlines

60
Q

Describe moraines

A
  • Push moraines are essentially formed by bulldozing sediment and then dumping it
  • formed as glaciers are advancing or retreating
  • Hummouky moraines are very different to push morraines. They are formed when a glacier begins to stagnate which is why they are sometimes referred to as stagnation morraines.
61
Q

Describe ice thickness and trimlines

A
  • Erosional tide mark that marks the upper limit of glacier occupancy.
  • Ice mounded bedrock below is weathered while shattered bedroc is above.
62
Q

How can we date the geomorphology of glaciation?

A

1) Identify moraines
2) Interpret climatic/environmental controls on moraines (climatic events)
3) Assess sediment including organic deposits in depressions between moraines
4) Dating- date peat, surface exposure of boulders etc

63
Q

Describe multiple glaciation

A
  • How do you tell multiple glaciers apart form each other?
  • Freshness of geomorphology
  • Superimposition of tills (oldest sediment at the bottom
  • Dating
64
Q

What are some of the problems with multiple glaciation?

A

A) Only a partial record due to erosion (ice sheets wipe away evidence)
B) Overprinting of events (palimpsest)
- Older glaciation are much more difficult to reconstruct and particularly problematic in terrestrial settings.

65
Q

What is a perglacial?

A
  • conditions, processes and landforms associated with cold, non-glacial environments regardless of their proximity to glaciers. Freeze-thaw processes
66
Q

What is a permafrost?

A
  • Perennially frozen soil or bedrock. Develops where mean annual air temps are less than 0 degrees.
67
Q

What are protalus ramparts?

A
  • Fossil snow patches that formed under colder conditions than today
68
Q

Name some perglacials formations or conditions

A

1) Perglacial conditions
2) Permafrost
3) Protalus ramparts (relics)

69
Q

What are some low latitude geomorphic features?

A
  • Pluvial lakes
  • Pluvials
  • Interpluvials
70
Q

What are pluvial lakes?

A
  • Lakes related to wetter climates
71
Q

What are pluvials?

A
  • Lengthy periods of rainfall
72
Q

What are interpluvials?

A
  • Low water or desiccation which indicates changes in moisture balance during the late Quaternary
73
Q

What are sand dunes?

A
  • Past periods of increased aridity
  • Expansion of dune fields in glacials
  • Dunes on pluvial lakes flows point to alternating wet and arid conditions.
  • Deposition of loess (wind blown silt with phases of activity)
74
Q

Give an example of a pluvial lake with sand dunes?

A
  • Mega-chad
75
Q

What can the past tell us?

A

1) Natural variability in environment
2) Rates of change- fast or slow
3) Spatial linkages
4) Thresholds and feedbacks
5) Empirical basis for modelling
6) Context for and evidence of human impact

76
Q

What is quaternary environmental change?

A
  • Quaternary (last 2.6 million) were dominated by ice ages

- Repeated growth and decline

77
Q

What is stratigraphy?

A
  • Study of sediments and the sequence of events they record
78
Q

What is lithostratigraphy?

A
  • Variations in lithology
  • Physical characteristics of rocks
  • Ordering of sediments
79
Q

What is biostratigraphy?

A
  • Fossils
80
Q

What is chronostratigraphy?

A
  • Radiocarbon dating etc
81
Q

What is morphostratigraphy?

A
  • Landforms
82
Q

How might we describe or sort sediment?

A
  • Grains size
  • Internal structures
  • Lateral variability
83
Q

What does sediment tell us about environmental change?

A
  • Interglacial deposits of different age found at different sites are compared using faunal flora
  • known distribution of modern species as a basis for palaeoclimatic inference
84
Q

What does changing flora tell us about environmental change?

A
  • Reconstructing former vegetation cover from pollen grains in sediments
  • Based an uniformitarian principles
  • Identifies part variations in climate and differentiates similar events of different age.
  • Pollen grains resilient to decay
85
Q

What does pollen overtime tell us about environmental change?

A
  • Younger drysas was a period right at the end of the last ice age.
  • It was a cold snap just when the climate was beginning to warm.
  • Lots of tundra during this time and a low treeless landscape
  • 10,000 years ago tree pollens increased and this is associated with the Birch tree
  • Over time more woodland canopies grew and this was reflective of the warming climate.
  • 5000 years ago elm dramatically declined and this was seen across Europe. This issue is still disputed but some theories include disease and human intervention
  • Pollen records are correlated with oxygen isotope signal.
86
Q

What does soil development tell us about environmental change?

A
  • Soils are a product of interaction between environmental conditions near the Earth’s surface
87
Q

What are the factors controlling soil development?

A
  • parent soil- unconsolidated rock/bed rock
  • Temperature and precipitation
  • Thickness of soil- time
  • Organisms irate the soil e.g. Fungi, earthworms
88
Q

What is palaeosoil?

A
  • Alternating sequence of lighter and darker soils
89
Q

What dating techniques are available to us?

A
  • Vital to know when and at what rate environmental changes occurred
  • Absolute dating- Assign an age to sediments using a specific technique
  • Relative age dating- Based on stratigraphy, establishing relative order of antiquity of fossils
90
Q

What is radiometric dating?

A
  • Based on the idea of stable and unstable isotopes
  • Radioactive decay is time dependent. If the rate of decay for a given element can be determined then age of host material Cana Lao be established.
91
Q

What is absolute dating?

A
  • Radioactive decay of the unstable isotope of 14C (radiocarbon) can be used for dating because all living things and therefore tissue decay contain carbon.
  • If you measure the remaining amount of carbon you get the age
  • e.g. Resolving the debate of the extent of the last glaciation in Ireland- 14C dates on reworked shells in glacial deposits show they date from extensive ice sheet coverage
92
Q

What is absolute dating (noncarbon)

A
  • Darker rock surface exposure to cosmic radiation

- The longer the roc has been exposed, the more cosmogenic isotopes.

93
Q

What is linchenometry?

A
  • Based on the principle that older lichen is bigger in size.
  • Involves a lot of assumptions
94
Q

What is a multi proxy approach?

A
  • It is best to use a variety of indications for dating
  • This removes many potential problems e.g. Local effects and ensures interpretation is not based on one piece of evidence.
95
Q

What is the Holocene?

A
  • Holocene period is the name for the period we are currently in and covers the last 11,500 years
96
Q

What is the quaternary period?

A
  • Pleistocene + Holocene periods
  • Period of high precision palaeoclimate reconstruction
  • Human population expansion
  • Glacial/interglacial transition
  • Human impact on climate change
97
Q

What characterised the end of the Pleistocene?

A
  • Late-glacial which was approximately 15,000 years ago. This was followed by the younger dryas stadial which was about 13,000 years.
  • The onset of the Holocene was marked by a rapid temperature increase. Ice core records suggest that MAAT increased by 7 degrees in 50 years
98
Q

What is historical data like for the climate?

A
  • World’s longest temp record is in central England and has been going since 1659.
99
Q

Describe the early Holocene thermal maximum- 9000 years ago .

A
  • Warmer than present in many areas by 1-2 degrees
  • Disappearance of polar ice shelves
  • Northward expansion of deciduous woodland reaching max range limits by 6000 years ago.
100
Q

Describe the medieval warm period- 750-1200 AD

A
  • Increased in temperatures (1-2 degrees)
  • Varied spatially not globally
  • Reduced sea ice led to settlement of viewings in Greenland 800-1000AD
  • Feature of colonies by mid 1300s
  • Vineyards in S Britain as recorded in the ‘Doomsday Book’
101
Q

Describe the little ice age?

A
  • 1500-1900 AD
  • Glacier expansion
  • Temperatures cooler 1-2 degrees
  • Peaked AD 1700 but persisted to 1900
  • Thames frost fair- river froze ones
102
Q

Describe current global warming

A
  • 0.85 degrees increase in average global temps from 1880- 2012
  • 4 of the 5 warmest years on record occurred since 1990
  • Global warming may not refer to the greenhouse effects or human related warming
103
Q

What are some other possible causes for short term climate change?

A

Earth’s cyclical climate changes are driven by

  • Orbital parameters (Milankovitch cycles)
  • Internal system feedbacks (e.g. Ice sheet albedo)
  • Solar output
104
Q

When will be the dawn of the next glaciation?

A
  • Proxy records of palaeoclimate = abrupt cooling always terminates interglacials
  • We are approximately half way through the interglacial period.
105
Q

What are the predictions fro future climate?

A
  • Use global circulation models to predict future climate. Earth’s surface is divided into a grid of boxes which extend vertically into the atmosphere.
  • Predictions assume occurrences based on past records
106
Q

What are the Milankovitch glacial- interglacial cycles?

A
  • Archives of glacier ice volume through time from stable isotope analysis
  • Glacial= depletion of 16O in ocean and enrichment in ice
  • Interglacial= enrichment of 16O in ocean water and depletion in ice.
107
Q

Describe rapid climate change

A
  • High frequency climate oscillations- interstadials of 500-2000 years of relatively mild climate during the last cold stage (80-20ka BP).
  • Dansgaard- Oeschger events- show gradual cooling followed by abrupt warming
  • Temperature changes of up to 7 degrees.
108
Q

Describe ice ranted debris in deep sea cores- Heinrich layers

A
  • Six conspicuous layers of ice rafter debris detected in North Atlantic sediment cores
109
Q

What is a Heinrich events?

A
  • Rapid advance of the last North American ice sheet during which an ‘iceberg armada’ was delivered into the North Atlantic
110
Q

What are Heinrich layers?

A
  • Layers of iceberg ranted debris resulting from melting of Heinrich event icebergs and deposition onto the sea floor.
111
Q

What are bond cycles?

A
  • Gerard Bond identified marine equivalents of the Dansgaard Oeschger cycles in the North Atlantic deep sea sediment cores
  • After an escape Italy large warming, the next DO cycle wouldn’t get quite as hot, with the next cooler still and so on
  • Largest cooling coincided with a Heinrich event.
112
Q

What are the causes of the Milankovitch events?

A
  • Variations in solar output is a major factor in short-term climate change
  • Alternating active + quiescent phases of solar activity as reflected in growth and disappearance of sunspots in a cyclical fashion.
  • How solar activity= fewer sunspots= global cooling
  • Principle: formation of NADW and operation of thermo-haline circulation (THC) is very sensitive to freshwater
113
Q

What are the potential causes of ice sheet growth and decay?

A
  • Denton model- says external factors

- ‘Binge-purge model’- says internal factors

114
Q

What is the bipolar seesaw?

A
  • Changes to the Thermohaline circulation
  • Principle= thermohaline seesaw (when Greenland is cold, Antarctica is warm)
  • Anti-phasing of climate and reorganisation of THC = bipolar seesaw

Physical Geography (5 decks)

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