Quaternary Glaciation Flashcards
(114 cards)
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.
2
Q
- What is the quaternary period?
A
- 2.6 million years ago to the present day
3
Q
What is the Holocene?
A
- 11.5 thousand years ago until the present day
4
Q
What might proxy data show?
A
- Regular and frequent climate fluctuations
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.
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.
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.
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.
9
Q
What are some examples of external forcing mechanisms in the climate system?
A
- Solar output and orbital patterns
10
Q
What are some examples of internal forcing mechanisms in the climate system?
A
- Feedback by earth’s elements (albedo, ocean currents)
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.
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?
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
14
Q
What were the causes of the Pliocene- Pleistocene transition?
A
- Disposition of land masses and ocean gateways
- Tectonic activity
- Feedback mechanisms
15
Q
Who was Alfred Wegener?
A
- Theorised continental drift
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)
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
18
Q
How did feedback mechanisms lead to the Pliocene- Pleistocene transition?
A
- Ocean-atmosphere circulations
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
20
Q
What happened in the Mid-Pleistocene transition?
A
- There was an intensification of glaciation since 800ka BP
- Why?
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
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.
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
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.
25
What did the Croll-Milankovitch theory say controlled glaciation?
- Glacial/interglacial periods due to cyclical changes in earth's orbit around the sun.
26
What did the Croll- Milankovitch theory say about eccentricity?
- 100ka and 400ka
| - Change in shape of earths orbit from circular to elliptical =0.03% max change in annual insolation receipt
27
What did the Croll- Milankovitch theory say about obliquity?
- 41ka
- Change in tilt of Earth's axis of rotation from 21.8 to 24.4 degrees
- Larger differences between seasons as tilt increases
28
What did the Croll- Milankovitch theory say about precession?
- 23ka and 19ka
- Wobble of earth on its axis due to gravitational attraction of sun and moon.
- Alters timing and variability of seasons.
29
What is a good example of cyclicity in the landscape?
- 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
30
Summarise why longer term climate change occurs?
- Multiple components of the earth-atmosphere system change including tectonics, orbital changes and volcanoes.
31
What doe every element contain?
- 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
32
Describe oxygen as an element
- 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.
33
What effect do oxygen isotopes have in reality?
- 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.
34
Describe oxygen in glacials
- O16 is evaporated from water earliest. Hence ocean waters are relatively enriched in O18 while ice sheets are more enriched in O16.
35
Describe oxygen in interglacials
- Melting ice sheets return more O16 to the ocean.
36
Describe the oxygen isotope records
- 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
37
What are the marine isotope stages?
- 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
38
What is the ocean core palaeoclimate record?
- 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
39
Describe ocean cores
- Increases during glaciation and provides a deep-sea record of ice sheet fluctuations.
40
What can ice cores tell us?
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)
41
How do ice cores tell us about past temps?
- Looking at the different oxygen isotopes for correlation with the marine record
42
How do ice cores tell about the gas content of the atmosphere?
- CO2, CH4 in bubbles in the ice
43
How does dust tell us about the past dust particles?
- Past aeolian activity and marker horizons
44
Describe ice cores and oxygen isotope analysis?
- 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
45
Describe ice core records of long-term climate change
- 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)
46
What are the different external and internal forcing functions and what are their specific spatial and temporal impacts?
- Different elements respond over different timescales
| - Long term climate changes involve progressively more components of the earth-atmosphere system.
47
What is the importance of fine-resolution palaeoclimate records (ice cores)- 'sub- Milankovitch' climate change.
- 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
Give an ocean example of earth's climate system and mechanisms?
- 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
What is the importance of fine resolution palaeoclimate records like oceans in deep sea core?
- 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
Define Heinrich events
- 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
Define Dansgaard-Oeschger cycles
- Rapid climate fluctuations during the last cold stage (~20 in number, with a periodicity between 1000-2000 years (thus sometimes called 'millennial cycles'
52
What are bond cycles?
- Longer term cooling cycles 10,000-15,000 years long during the last cold stage.
53
Describe ice core/ocean core correlation and fine resolution records
- High frequency climate oscillations - long term cooling cycles and abrupt warming (bond cycles) = climate's flickering switch
54
What is the most powerful means of palaeoclimate reconstruction?
- 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
What are quaternary glacials?
- Large areas of mid to high latitudes of the northern hemisphere were covered by large ice sheets e.g. North America, UK, Switzerland
56
Describe palaeoclimatology or the reconstruction of former ice cores
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
Describe ice flow directional landforms
- 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
Describe subglacial landform Drumlins
- Elongated in direction of glacial flow
| - Blunt upstream and with a tapered end or tail
59
Name some former glacier margins
1) Moraines
| 2) Trimlines
60
Describe moraines
- 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
Describe ice thickness and trimlines
- Erosional tide mark that marks the upper limit of glacier occupancy.
- Ice mounded bedrock below is weathered while shattered bedroc is above.
62
How can we date the geomorphology of glaciation?
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
Describe multiple glaciation
- How do you tell multiple glaciers apart form each other?
- Freshness of geomorphology
- Superimposition of tills (oldest sediment at the bottom
- Dating
64
What are some of the problems with multiple glaciation?
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
What is a perglacial?
- conditions, processes and landforms associated with cold, non-glacial environments regardless of their proximity to glaciers. Freeze-thaw processes
66
What is a permafrost?
- Perennially frozen soil or bedrock. Develops where mean annual air temps are less than 0 degrees.
67
What are protalus ramparts?
- Fossil snow patches that formed under colder conditions than today
68
Name some perglacials formations or conditions
1) Perglacial conditions
2) Permafrost
3) Protalus ramparts (relics)
69
What are some low latitude geomorphic features?
- Pluvial lakes
- Pluvials
- Interpluvials
70
What are pluvial lakes?
- Lakes related to wetter climates
71
What are pluvials?
- Lengthy periods of rainfall
72
What are interpluvials?
- Low water or desiccation which indicates changes in moisture balance during the late Quaternary
73
What are sand dunes?
- 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
Give an example of a pluvial lake with sand dunes?
- Mega-chad
75
What can the past tell us?
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
What is quaternary environmental change?
- Quaternary (last 2.6 million) were dominated by ice ages
| - Repeated growth and decline
77
What is stratigraphy?
- Study of sediments and the sequence of events they record
78
What is lithostratigraphy?
- Variations in lithology
- Physical characteristics of rocks
- Ordering of sediments
79
What is biostratigraphy?
- Fossils
80
What is chronostratigraphy?
- Radiocarbon dating etc
81
What is morphostratigraphy?
- Landforms
82
How might we describe or sort sediment?
- Grains size
- Internal structures
- Lateral variability
83
What does sediment tell us about environmental change?
- 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
What does changing flora tell us about environmental change?
- 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
What does pollen overtime tell us about environmental change?
- 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
What does soil development tell us about environmental change?
- Soils are a product of interaction between environmental conditions near the Earth's surface
87
What are the factors controlling soil development?
- parent soil- unconsolidated rock/bed rock
- Temperature and precipitation
- Thickness of soil- time
- Organisms irate the soil e.g. Fungi, earthworms
88
What is palaeosoil?
- Alternating sequence of lighter and darker soils
89
What dating techniques are available to us?
- 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
What is radiometric dating?
- 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
What is absolute dating?
- 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
What is absolute dating (noncarbon)
- Darker rock surface exposure to cosmic radiation
| - The longer the roc has been exposed, the more cosmogenic isotopes.
93
What is linchenometry?
- Based on the principle that older lichen is bigger in size.
- Involves a lot of assumptions
94
What is a multi proxy approach?
- 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
What is the Holocene?
- Holocene period is the name for the period we are currently in and covers the last 11,500 years
96
What is the quaternary period?
- Pleistocene + Holocene periods
- Period of high precision palaeoclimate reconstruction
- Human population expansion
- Glacial/interglacial transition
- Human impact on climate change
97
What characterised the end of the Pleistocene?
- 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
What is historical data like for the climate?
- World's longest temp record is in central England and has been going since 1659.
99
Describe the early Holocene thermal maximum- 9000 years ago .
- 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
Describe the medieval warm period- 750-1200 AD
- 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
Describe the little ice age?
- 1500-1900 AD
- Glacier expansion
- Temperatures cooler 1-2 degrees
- Peaked AD 1700 but persisted to 1900
- Thames frost fair- river froze ones
102
Describe current global warming
- 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
What are some other possible causes for short term climate change?
Earth's cyclical climate changes are driven by
- Orbital parameters (Milankovitch cycles)
- Internal system feedbacks (e.g. Ice sheet albedo)
- Solar output
104
When will be the dawn of the next glaciation?
- Proxy records of palaeoclimate = abrupt cooling always terminates interglacials
- We are approximately half way through the interglacial period.
105
What are the predictions fro future climate?
- 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
What are the Milankovitch glacial- interglacial cycles?
- 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
Describe rapid climate change
- 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
Describe ice ranted debris in deep sea cores- Heinrich layers
- Six conspicuous layers of ice rafter debris detected in North Atlantic sediment cores
109
What is a Heinrich events?
- Rapid advance of the last North American ice sheet during which an 'iceberg armada' was delivered into the North Atlantic
110
What are Heinrich layers?
- Layers of iceberg ranted debris resulting from melting of Heinrich event icebergs and deposition onto the sea floor.
111
What are bond cycles?
- 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
What are the causes of the Milankovitch events?
- 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
What are the potential causes of ice sheet growth and decay?
- Denton model- says external factors
| - 'Binge-purge model'- says internal factors
114
What is the bipolar seesaw?
- 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
