Quaternary: Lectures 14-19

Question 1

Outline key characteristics of the Quaternary.

Answer 1

Last 2.6 million years
Divided into Pleistocene and Holocene (11.5k - now)
Characterised by glacial-interglacial cycles (the cyclic growth & decay of huge continental ice sheets)
We are currently in the Holocene, an interglacial

Question 2

How has ppm changed over time? Why is it significant today?

Answer 2

280ppm before industrialisation
400pm passed in 2015
Projected 1200ppm by 2100AD; not seen in last 1000 or more yrs

Question 3

Define catastrophism and uniformitarianism/gradualism

Answer 3

Catastrophism = all land features a result of successive, individual catastrophic events

Uniformitarianism = land features a result of gradual, small-scale events

Question 4

Name key geological academics, what did they say?

Answer 4

1. Charles Lyell - “present is the key to past”
2. James Hutton - “past is key to future”
3. Luis Agassiz - first to theorise processes/cycles of cooling and warming (glacials and interglacials)
4. Milankovitch - cycles used to explain mechanism behind waxing and waning ice sheets

Question 5

What are Milankovitch Cycles?

Answer 5

Orbital forcing on the Earth that create solar variability, altering the Earth’s climate:

1. Eccentricity - roundness of orbit (100kyrs, and also 400kyrs!)
2. Obliquity - tilt of axis, currently at 23.44 (41kyrs)
3. Precession - axial wobble (25kyrs)

Perihelion = closest to Sun

Question 6

How were the first records for palaeoclimatology taken?

Answer 6

Marine records:

• 1947 seismology, shallower sediments
• 1950s paleomagnetism
• 1960s Deep Sea Drilling
• 1970s John Imbrie analysis of G. bulloides O-isotopic composition in shells

Ice Core records:

• 1820 1st continental ice shelf sighting
• Greenland ice cap not confirmed until late 1800s
• 1950s ice sheet drilling

Question 7

Describe ice cores - how far back do they take us and what can they tell us?

Answer 7

High resolution, up to 3km long, across both hemispheres…

Antarctic ice sheet - contains oldest ice cores (800,000 yrs, potentially further now to 2 Ma!); 4.5km thick
Greenland ice sheet - only 130,000 yrs; 2.4km thick

Isotopic composition indicates temperatures: 18O-enriched ice core suggests warmer temps
Can be correlated with marine cores: 18O-enriched core suggests cold because less evaporation

Question 8

What is radiocarbon dating and why can’t it be used all the time? What other proxies are used?

Answer 8

Radiocarbon dating (14C) - radioactive carbon indicate age but loses precision and accuracy after 50k/60k yrs

Speleothems = caves; bands, isotopes indicate climate
Trees (dendroclimatology) = high resolution bands, indicates moisture, climate, temp
Pollen/plants = in peat/lakes, indicator species of temp and climatic conditions
Chironomids = non-biting midges; specific temp, O, pH requirements
Beetles = warmer temp-specific species (Russell Coope)
Forams = O and C composition of shells, indicates water temp
Mammals = dating, marks…
Coral = SST
Testate amobea = peatland water table

Question 9

Name the 4 continental ice sheets of the Northern Hemisphere Quaternary that would have experienced cyclic growth and degrowth

Answer 9

N. America - Laurentide and Cordilleran
Europe - British and Scandinavian
Russia - Barents and Kara
Greenland

Question 10

What/when was the last glacial?

Answer 10

Last glacial period Devensian
- Interstadials identified within this period (smaller warm periods within a glacial)
(Not the LGM which was 22ka!)

Question 11

Describe the British Ice Sheet during the Devensian or LGM.

Answer 11

Covered all of Scotland and Wales (800,000 km2, 1.5km thick)
- Diagonal maximum extent (so didn’t cover places like Bristol, Oxford or Cambridge)

Evidence:

• Terminal moraines
• Contested e.g. small glaciers on Exmoor, Dartmoor, erratics in N. Devon

Question 12

Describe sea level change in the Quaternary and resulting landforms?

Answer 12

Eustatic (with global ice volume) and Isostatic (localised, ice loading like Britain)

125m lower during LGM = Doggerland, land bridges = plant, animal, human dispersal
- Rapid change, 16-25m rise in just 400-500 yrs

Evidence: wave-cut platforms, raised beach deposits, marine fossils

• Hope’s Nose Peninsula, S. Devon
• Huon Peninsula, Papua New Guinea

Question 13

What caused the end of the last ice age (last glacial Devensian)?

Answer 13

1. Increased summer insolation at higher N latitudes; maximum obliquity and perihelion
2. Increased atmospheric CO2 from 190-280ppm; ocean degassing, biomass feedbacks (increased CO2 respiration)

Question 14

What made the end of the Devensian complex? What evidence do we have of deglaciation?

Answer 14

Not smooth into Holocene e.g. 15ka warming and other interstadials/stadials

• ‘Late glacial’
• Younger Dryas

Biome shifts - expansion of oak woodland, contraction of tundra
Doggerland flooded, submerged 8,200 yrs ago (freshwater pulses)
Animals indicate fertility of the land e.g. mammoth teeth, lions, human tools

Question 15

What were the two ice sheets either side of Rocky Mountains called?

Answer 15

Laurentide (3km thick, 33 M km3)

Cordilleran (merged with Laurentide in LGM)

Question 16

What is significant about research on the North Atlantic and Northern Hemisphere?

Answer 16

Dominated research in past - historical bias
Teleconnections - is the NA a driver of global change?
Significant processes within this region - NAO and AMOC

Question 17

Outline NAO and AMOC in the context of ice ages.

Answer 17

North Atlantic Oscillation:

• Air pressure gradient between subpolar low and subtropical high
• N. Atlantic jet stream strength/position influenced
• Affects temp & precipitation
• Positive (strong gradient, jet stream N) / Neg (weak)

Atlantic Meridional Oceanic Circulation

• N flow of warm, saline surface water keeps Europe warm
• S. flow of colder deep water, transports heat energy from tropics and SH to N. Atlantic
• Causes disruption during deglaciation (freshwater, less deep water formation etc)

Question 18

What are Dansgaard-Oeschger events and Heinrich events? How many in late Quaternary and what are the potential drivers?

Answer 18

D-O events:

• Abrupt/rapid warming (interstadials)
• Last 500-2000 yrs
• 25 in last glacial
• 5-8C temp rise in just 40 yrs!!??
• More muted in SH

Heinrich:

• Cooling before D-O in some cases
• Cooling every 10k yrs with southward dloating ice discharges
• 6 in late Quaternary
• Transportation of ice-rafted debris into N. Atlantic

Links between them possible…
Internal forcing - NAO changes from freshwater pulse, ice sheet dynamics/changes
External forcing - solar, orbital, periodicity

Question 19

Outline deglaciation in N. America. What have such discoveries meant for studies into human dispersal and megafauna in N. America?

Answer 19

• Proglacial lakes formed (terminal moraine dams)
• Rapid Cordilleran melt = megafloods (17M m3/sec) in Missoula and Columbia
• Staged catastrophic collapse of Lake Agassiz = 20-40cm global sea-level rise
• Freshwater pulse = NAO disruption?

Movement of humans into N. America?

• N. America 15ka
• 125m lower sea-levels, Alaksa-Russia land bridge
• Somehow ppl moved to N. America; before Cordilleran/Laurentide fusion? - ice-free corridor route vs. pacific coast route hypotheses

Megafauna mass extinction 11ka

• Sabre tooth tiger, Smilodon, Mastadon, Mammathus, Megatherium
• Caused by human hunters or climate changes?

Question 20

Why is it important to study Asia and the tropcis?

Answer 20

Population: >3 bn ppl
Climate: NAO, SAM, SWWB, ACC, ENSO, Monsoons, ITCZ
No continental ice sheets - elsewhere e.g. NZ, Patagonia, E. Africa, Papua New Guinea
New archives/proxies
Hemispheric differences
Hominid evolution, agriculture
Hurricanes
Biggest portion of world’s wetlands (GHGs)

Question 21

Importance of the Himalayas?

Answer 21

Indian-Eurasian collision - mountain building
- Si weathering increase –> C sequestration in deep ocean –> reduced atmospheric CO2 –> cooling climate = Quaternary ice age 2.6 Ma

Question 22

Describe the Asian monsoon and its 3 main components.

Answer 22

Seasonal reversal of wind direction - dramatic precipitation changes

• Driven by strong presure gradients = heating in Asian summer, L to H, bring moist SW Pacific air
• Pressure gradients reverse = H to L pressures, cooling Asia

1. East Asian Summer Monsoon (EASM)
2. Indian Summer Monsoon (ISM)
3. Western North Pacific Summer Monsoon (WNPSM)

Question 23

What are Loess deposits - what do they show us?

Answer 23

Fine-grained, wind-blown material

• Largest in N. China, Lanzhou
• 10-50m thick deposits; thickest in cold periods, breaks down in warmth so analysis can indicate glacial-interglacials
• Size of grains indicate wind strength = monsoon winds
• Loess and GROP 18-O records over shorter (sub-Milankovitch) timescales; connected to N. Atlantic?

Quaternary loess in discontinuous belt in S. Asia, small amounts in Kent and Cornwall

Question 24

What new proxies are available from Asia?

Answer 24

Ice cores from Tibetan plateau (3rd pole) = 4 ice caps, 600,000 yrs old

Speleothems from Dongee & Hulu caves = high resolution

• Uranium-Thorium dating
• O isotope proxy for monsoon changes
• Weakening of Asian monsoon 8ka-2ka

Question 25

What are the ITCZ and ENSO in context of glacial-interglacials?

Answer 25

Inter-tropical Convergence Zone:

• Maximum insolation; rising air; high rainfall; low pressure where N/S trade winds meet = doldrums
• Evidence of such climate in records, changes could be identified

El Nino Southern Oscillation:

• La Nina normal cooling phase with cold water upwelling by S. America, warmth in W. Pacific
• El Nino = westerlies weaken, warm lid on upwelling, pressure gradient switches
• Changes have global impact - storms, crop failure, drought

Question 26

How have climatic changes been reconstructed?

Answer 26

Coral reefs e.g. porites

• Annual bands, 200 yrs if alive, 1000yrs from fossils
• O isotopes reflect Sea Surface Temp
• Huge gaps in record currently; differences between NH and SH identified

African lake levels:

• Ancient shorelines, sediments, isotopes, fossils
• Lake level change indicates atmospheric circulation/rainfall changes
• Some correlation with N Atlantic events

Question 27

What significant change/period has been identified within N. Africa?

Answer 27

African humid period where Sahara Desert was green!

• Abundant flora & fauna (hippos, giraffes, primates)
• Palaeolithic cave art animals (6ka)
• Evidenced by a lack of terrestrial dust in western coast cores
• Material in core dramatically shifted, suggests humidity shifted southwards rapidly - but cause is uncertain

Question 28

Describe Southern Ocean - why ocean so important?

Answer 28

The ocean south of 60S latitude
Hosts Antarctic Convergence - Antarctic meets warmer Atlantic, Paciifc and Indian waters
High biodiversity and productivity
Contains longest, strongest Antarctic Circumpolar Current - means of exchange between ocean basins

Largest carbon reservoir (espec deep)
80% deep water upwelling in SO driven by strong westerlies - chance to release CO2

Question 29

What are the 2 major climatic systems in this region? Proxies for these?

Answer 29

Southern Westerly Wind Belt:
(Northern westerlies = stronger in winter, interrupted by land masses, gyres and differential heating)
- Southern westerlies = strongest, uninterrupted winds in world; roaring 40s, furious 50s, screaming 60s
- SWWB strength/position determines whether SO is source or sink of CO2

Southern Annular Mode:

• Antarctic and mid-SH latitude pressure gradient
• Positive SAM = strong lows over Antarctica, highs further N; forcing SWWB further S = greater deep Antarctic upwelling = more CO2 released?

Precipitation often used to indicate wind-speeds of past (a proxy for SAM?)

Limited land mass for proxies - Patagonia, New Zealand, Antarctic Peninsula

Question 30

Outline recent research in Patagonia.

Answer 30

SWWB reconstructions using testate amoebae numbers in peat cores

• Identified by morphology, can indicate water table depth and annual water balance
• Rise in particular testate species = dryer conditions or simply just bcos more resistant to UVB in light of 70s ozone depletion?

Question 31

Outline recent research in New Zealand. Why such a good location?

Answer 31

Peat cores with different restiad (rush) species - research into O isotope composition related to atmospheric moisture/temp

An excellent location:

• Low/high pressure boundary
• Tropical and polar influences
• Strength and position of SWWB reflected by its climate
• Understanding of SAM and SO changes

Question 32

Outline recent research on Antarctic Peninsula

Answer 32

5000 yr old moss banks
3C warming since 1950s
Since 1957 in records, sudden and dramatic response to anthropogenic warming - productivity, growth rate, accumulation rate = “the great acceleration” is clear

Question 33

Using Antarctic and Souhern Hemisphere records together, what can be inferred?

Answer 33

Ice cores:
- CO2 and CH4 changes and isotopic comp indicating temp

Other events causing changes in ice cores:

• Volcanic ash: tephra chronology, bcos of SWWB, ash from Patagonia found in Antarctic
• Dust and sea spray: changing concentration suggests changing source, distributed by SWWB - indicating atmospheric circulation and glaciation changes
• Saltiness; a proxy for storminess, sea-ice extent?

Question 34

How can climate reconstructions help our understanding of the first people of S. America and the Pacific?

Answer 34

S. America:

• Oldest arhcaeology 14.5 ka in Monte Verde, S. Chile
• Oldest remains before the Cordilleran ice sheet retreat - Pacific coast route hypothesis

Pacific:

• Lower LGM sea level
• Australia 40-80ka
• Early arrival?
• Megafauna extinction 46ka could have been anthropogenic?