Quaternary Period

Question 1

How does quaternary period relate to climate change

Answer 1

• The Quaternary period (the last 2.6 million yrs) has been dominated by long cold, glacial cycles separated by short, warm interglacials.

Question 2

Major timescales

Answer 2

• Cenozoic climate change – long term geological context
• Quaternary Period (2.6 Ma to present day). show regular & frequent climate fluctuations
• The Holocene (c. 11.5 ka to present day)

Question 3

Drivers of climate change: How does climate work on Quaternary timescales

Answer 3

• ‘Forcing function’
- Is a mechanism that causes a system to change from its equilibrium state.
- driven by perturbations in the earth-atmosphere system
• External forcing: extra-terrestrial/non-earth processes e.g. solar output & orbital patterns
• Internal forcing: driven by earth processes e.g. albedo, ocean currents, GHG’s
 positive feedbacks (amplifies changes in the climate system)
negative feedbacks (counter changes within a system)

Question 4

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

Answer 4

• Increased global volcanism
• First evidence of widespread glaciation (esp. in N. Hemisphere) = deep ocean cores reveal larger & more persistent volumes of ice-rafted debris at c.2.6Ma BP
• Cores also show increase in volcanic ash from 2.6Ma = increased global volcanism
 SO2 aerosols (increase in earth’s albedo?)

Question 5

The pattern and nature of Quaternary climate change

Answer 5

• There are very distinctive patterns/cycles in Quaternary climate records
• Climate cycle periodicity (rhythm)
• - 41,000yrs prior to ~800ka BP
- 100,000yrs after 800ka BP
• Intensification of glaciation since 800ka BP = Mid-Pleistocene Transition
• Why the change in rhythm at 800ka BP?
• The cycles are driven by orbital forcing (external forcing) which is controlled by our relationship to the sun

Question 6

How does Orbital forcing cause climate change - Milankovitch theory

Answer 6

• Main premise = changes in intensity of seasons in Northern Hemisphere (NH) control ice sheet inception & decay
• NH high latitude summer temps key to the onset of glaciation. If cold enough winter snows would not completely melt & would grow into glaciers.
• Earth’s distance from the sun varies seasonally
- perihelion (nearest in NH winter)
- aphelion (furthest away in NH summer)

Question 7

Milankovitch cycle

Answer 7

Eccentricity: (100ka & 400ka) Change in shape of Earth’s orbit from circular to elliptical
= 0.03% max change in annual insolation receipt. Dominant post 800ka.
-Obliquity: (41ka) - Change in tilt of Earth’s axis of rotation from 21.8o-24.4o
 Larger differences between seasons as tilt increases. Dominant pre 800ka.
-Precession: (23ka & 19ka) - Wobble of Earth on its axis due to gravitational attraction of sun & moon. Alters timing & variability of seasons.

Question 8

Oxygen isotopes - principles

Answer 8

• Every element has a number of protons which give it a unique atomic number (e.g. oxygen = 8)
• Every element also has a number of neutrons, which give it an atomic weight, BUT, this number can vary
• Oxygen can have 7, 8, 9 or 10 neutrons, which (added to the number of protons) gives isotopes of mass 15O, 16O, 17O, 18O
• These isotopes are heavier (e.g. 18O) or lighter (15O) than each other

Question 9

Oxygen isotope analysis - principles

Answer 9

• Variations in the ratio of 16O & 18O indicate changing isotopic composition of ocean waters between glacials & interglacials
• 16O/18O ratio in seawater is largely controlled by fluctuations in land-ice volume. Down-core variations record glacial/interglacial climatic oscillations
• Glacial: 16O is evaporated from water more easily. Hence ocean waters are relatively enriched in 18O while ice sheet relatively enriched in 16O.
• Interglacial: melting ice sheets returned more 16O to the ocean

Question 10

Oxygen isotope records

Answer 10

• Our record of glacier ice volume through time comes from analysis of marine microfossils in ocean floor sediments & ice cores
• Glacial = 16O depletion in ocean & enrichment in ice
• Interglacial = 16O enrichment in ocean & depletion in ice
• Analysis of marine sediment cores from the worlds ocean basins provides us with a coherent record of long term climate change

Question 11

‘Proxy’ data sources:Biogenic sediments

Answer 11

Biogenic sediments form from the skeletal remains of calcareous organisms (e.g., planktonic & benthic foraminifera –microfossils)
 i) record isotopic balance of the water they inhabited(related to water temp & salinity)
ii) relative abundance
iii) morphology/species
iv) preservation

Question 12

Proxy data sources: ) inorganic/terrigenous sediment and ice rafted debris (IRD)

Answer 12

• Increases during glaciations & provides a deep-sea record of ice sheet fluctuations

Question 13

Ice cores – what can they tell us?

Answer 13

• Temp:. ( 18O)(basis for correlation with marine record)
• Gas content of atmosphere :(CO2, CH4 in bubbles in the ice)
• Dust (particles): Past aeolian activity & marker horizons.
• Volcanic eruptions :(sulphur; tephra)
• Annual layers: (dating technique)

Question 14

interstadials/stadials within glacial/interglacial cycles
• What drives them?

Answer 14

• Some appear to have a cyclity during the last cold stage (80–20ka BP).
• Temperature changes of 7˚C between warm & cold stages. Abrupt start; more gradual decline (saw-tooth pattern)
• Particularly prevalent in the Greenland ice core records

Question 15

Sub-Milankovitch Climate Change

Answer 15

• Dansgaard–Oeschger cycles / D–O events – rapid climate fluctuations during the last cold stage; ~20 in number, with a periodicity between 1000-2000 yrs. First discovered by Willi Dansgaard in the 1970s and written off as ‘noise’
• Bond cycles – longer term cooling cycles 1,000-15,000 years long during the last cold stage - long cooling cycles & abrupt warming (Bond cycles)
• Heinrich events – marked by layers rich in ice-rafted debris (IRD) in marine sediment cores, which record massive iceberg discharges (binge/purge cycles of ice sheets; MacAyeal, 1992) with a ~cyclic occurrence. H’ Events tend to coincide with the end (cold phase) of Bond Cycles. Sediment is brought into teh ocean via ice sheets that cause a cooling and less salinity.

Question 16

Sub-milankovitch forcing

Answer 16

• There are multiple factors that drive/influence these sub-milankovitch changes. The include ocean circulation, atmospheric circulation, ice/fresh water flux to the ocean; ice sheet growth and collapse
-hypothesized the long-term, collective effects of changes in Earth’s position relative to the Sun are a strong driver of Earth’s long-term climate
-high frequency climate changes

Question 17

Sub-milankovitch forcing: Thermohaline circulation

Answer 17

Thermohaline circulation = temperature & salinity-driven currents initiated by:
a) cooling of surface water & increasing of its density
b) addition or removal of freshwater (e.g. iceberg armadas; lake bursts)
• The strength of the Thermohaline circulation is sensitive to freshwater input (reduces density so harder to sink ; it can slow down/stop – hence patterns of cooling/warming in N Atlantic region are very sensitive to ice sheet growth and decay as freshwater flux can effect North Atlantic Deep Water (NADW) overturn

Question 18

Sub-milankovitch forcing: Ice-Rafted Debris (Heinrich Layers) and ice sheet binge/purge cycles

Answer 18

• Six layers of Ice Rafted Debris (IRD) detected in North Atlantic sediment cores –’Heinrich Layers’ from the Laurentide ice sheet
• Heinrich Layers (H1-H6) deposited ~70-14 ka BP. Frequency 7-10 ka yrs
• We now know that the British and Fennoscandian ice sheets also delivered IRD to the N Atlantic.
• Ice sheet binge/purge cycles
• MacAyeal (1993) suggested ice sheet cyclical growth and decay was important for iceberg and freshwater flux to the ocean ……which subsequently influences thermohaline circulation
• Can one ice sheet collapse trigger another?

Question 19

What are the different types of Sediments ordering & Stratigraphy

Answer 19

• Stratigraphy = study of sediments & the sequence of events they record
• Lithostratigraphy - ordering of sediment successions through observable variations in lithology – e.g. sedimentary structures, clast lithology.
• Biostratigraphy - ordering of sediment successions through the use of fossils - e.g. pollen. Usually used for interglacials due to richer fauna & flora.
• Morphostratigraphy – based on landforms (erosional or depositional). The chronological subdivision of landforms in terms of their relative age based on their surface form
• Chronostratigraphy - ordering of sediment successions through dated levels - e.g. use of radiocarbon dating

Question 20

Sediments and Stratigraphy: Lithostratigraphy

Answer 20

Ø Ordering of sediment successions by variations in lithology
Ø Principle of stratigraphic superimposition
Ø Sediment found in cores or outcrops
Ø Sediments: clastic & biogenic
Ø : If we study and understand modern sedimentray processes we can use sedimentary evidence to infer past processes

Question 21

Sediments and Stratigraphy: Biostratigraphy

Answer 21

• Ordering of sediment successions through the use of fossils e.g. pollen. Usually used for interglacials due to richer fauna & flora
• Mainly based on faunal/floral fossil assemblages but also includes evidence of human presence.

Question 22

Sediments and Stratigraphy: Morphostratigraphy

Answer 22

• Based on landforms (erosional or depositional). The chronological subdivision of landforms in terms of their relative age based on their surface form.
• New frameworks for Quaternary morphostratigraphy (e.g.Candy et al., 2010; Lee et al. 2018)

Question 23

What are proxies

Answer 23

• There a many different proxies that can be used to reconstruct palaeo-environmental change:
• Flora & fauna (e.g. pollen, coleopteran, chironomids, diatoms; molluscs; ostracods)
• Physical properties, organic proxies, geochemical proxies (e.g. grain size; Magnetic susceptibility, bulk density, TOC, LOI, pigments, XRF, XRD)
•isotopes
•ice caps
• soil
•tree stumps/rings

Question 24

Proxies: Coleoptera and chironomids

Answer 24

• Insects = abundant & temperature sensitive – coleoptera (beetles) & chironomids (midges)
• Exoskeletons are robust & preserve detail (chitin) & can thus be identified to species level.
• Beetles (coleoptera) are highly sensitive to their environment & thus can be used to reconstruct palaeoclimate.
• Palaeoclimatic reconstructions are based upon modern distributions

Question 25

Dating techniques: absolute, radiometric incremental, relative

Answer 25

•Absolute dating – when an age estimate is assigned. Obtained using radiometric dating or Incremental dating
• Radiometric dating calculates an age by measuring the presence of a short-life radioactive element (e.g., carbon-14) or a long-life radioactive element plus its decay product (e.g., potassium-14/argon-40)
• Incremental dating allows the construction of year-by-year annual chronologies, which can be temporally fixed or floating (e.g. ice cores; varves)
• Relative age dating – can establish the relative order of antiquity of fossils or stratigraphic units. Often based on stratigraphy (principle of stratigraphic superposition - oldest unit at base, youngest at top) or comparison of a measurable parameter (e.g. Rock Surface Weathering; Amino Acid Geochronology)

Question 26

Radiometric dating

Answer 26

• Argon-Isotope
• Uranium-Series
• Cosmogenic Nuclide
• Radiocarbon

Question 27

Radiation Exposure Dating

Answer 27

• Optically stimulated Luminescence
• Electron Spin Resonance
• Fission Track
• incremental Dating Using Annually Banded Records.
• Dendrochronology
• Varves
• Annual Layers in Glacier Ice

Question 28

Relative Dating Methods.

Answer 28

• Rock Surface Weathering
• Obsidian Hydration dating
• Pedogenesis
• Relative Dating of Fossil Bone
• Amino Acid Geochronology

Question 29

Techniques for Establishing Age Equivalence

Answer 29

• Oxygen Isotope Chronostratigraphy
• Tephrochronology
• Palaeomagnetism
• Palaeosols

Question 30

Sub-Milankovitch scale changes

Answer 30

• Dansgaard–Oeschger cycles / D–O events – rapid climate fluctuations during the last cold stage; ~20 in number, with a periodicity between 1000-2000 yrs. First discovered by Dansgaard in the 1970s and written off as ‘noise’. Temperature changes of 7˚C between warm & cold stages.
• Bond cycles – longer term cooling cycles 10,000-15,000 years long during the last cold stage - long cooling cycles & abrupt warming (Bond cycles)
• Heinrich events – marked by layers rich in ice-rafted debris (IRD) in marine sediment cores, which record massive iceberg discharges (binge/purge cycles of ice sheets; MacAyeal, 1992) with a ~cyclic occurrence. H’ Events partially coincide/or occur just after the end (cold phase) of Bond Cycles?

Question 31

External forcing 1: what events were caused by Solar Irradiance

Answer 31

• Variation in solar output is a major factor in short-term climate change.
• Alternating active & quiescent phases of solar activity as reflected in growth & disappearance of sunspots in a cyclical fashion.
• Sunspot numbers vary on 11, 22, 80, 200 & 2000 yr cycles (R number)
• Maunder Minimum (1645-1715 AD)  Little Ice Age cooling – decrease in sunspot activity.
• Medieval warm period (1000-1200 AD) - peak in sunspot activity (+ decrease in volcanic activity).
• Recent work suggests the link between sunspots and climate events such as the LIA and Med warm period is tenuous (Owens et al,. 2017 )
• LIA spans 1440–1920, although not all of this period was notably cold.
• While the MM occurred within the much longer LIA period, the timing of the features are not suggestive of causation and should not, in isolation, be used as evidence of significant solar forcing of climate.
• Climate model simulations suggest multiple factors, particularly volcanic activity, were crucial for causing the cooler temperatures

Question 32

Internal forcing: 1. Ice sheet growth & collapse & ocean Thermohaline Circulation (THC)

Answer 32

• Principle: formation of NADW & operation of THC is v. sensitive to freshwater.
  A) Heinrich Events - reduction of SSTs & freshening of North Atlantic by icebergs.
   Rapid shutdown of THC & cessation of northward heat transport = cold temps.
  B) Cessation of iceberg calving as ice sheet retreats from deepwater
   increase in salinity
   rapid strengthening of THC
   rapid rise in North Atlantic temps
   ‘salt oscillator’ model

Question 33

Internal forcing 1: Ice-Rafted Debris (Heinrich Layers) and ice sheet binge/purge cycles

Answer 33

Ice sheet binge/purge cycles – ice sheet dynamics = main control mechanism
MacAyeal (1992) suggested ice sheet cyclical growth and decay was important for iceberg and freshwater flux to the ocean ……which subsequently influences thermohaline circulation

Question 34

Internal forcing 2: Freshwater Forcing of the Younger Dryas cold episode (12.8 - 11.7 ka) and the 8.2 ka event

Answer 34

• Deglaciation punctuated by the Younger Dryas. Severe cold. Ended v. abruptly with ~7 °C warming. Worldwide impact
• YD forced by freshwater outburst from Glacial Lake Agassiz – a proglacial lake of the Laurentide Ice Sheet
• But with ice sheet retreat northward drainage took place down St Lawrence River valley & into the Labrador Sea and possibly to the NW.
• Cooler temps across the North Atlantic triggered ice sheet regrowth (e.g. see Lecture 4 for Younger Dryas/Loch Lomond Stadial)
8.2 ka event - strong early Holocene cooling event (falls between Younger Dryas & LIA in amplitude).
Forced by final drainage of Glacial Lake Agassiz via Hudson Bay (Kleiven et al., 2008; Li et al., 2012)
Clear signal of freshwater into the Labrador Sea
Immediate North Atlantic cooling; Greenland Ice Sheet regrowth (Young et al., 2013); sea-level jump recorded along the Mississippi coast (Li et al., 2012)

Question 35

External forcing 2: A Bolide impact as the trigger for Younger Dryas cooling?

Answer 35

• In 2007 Firestone et al. suggested the YD event was the result of a bolide/meteor impact in North America.
• They cited convincing evidence for the termination of Clovis culture and megafaunal extinction based on:
• Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal,(iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with extra-terrestrial (ET) helium
• The bolide impact theory was widely refuted due to a lack of wider evidence (See Carlson et al. 2010).
• …….but the subject of meteorite impacts and climate change has recently reared its head again.

Question 36

Holocene climatic events: climate trends from proxy & historical data

Answer 36

• Early Holocene thermal maximum (thermal optimum, hypsithermal) 9-5ka.
– Warmer than present in many regions by 1-2oC.
– Most intense at the Poles (Renssen et al., 2012). Disappearance of polar ice shelves.
– Northward expansion of deciduous woodland reaching max range limits by 6 ka.
• The Neoglacial The HTM was followed by the late Holocene Neoglacial –climatic deterioration 4.5 – 2.5ka. Clear evidence across the N Hemisphere.
• The Neoglacial culiminated in the LIA.
• For example, evidence from Greenland for ice sheet re-growth, isostatic depression, sea-level rise, ice shelf regrowth (Smith et al. 2023).

Question 37

Little Ice Age (1500-1900 AD)

Answer 37

• Expansion of glaciers due to lack of radiation and sun spots
• Southward migration of Arctic sea ice
• Temperatures cooled 1-2°C
• Peaked c. AD 1700, but persisted to 1900
• Thames Frost Fairs

Question 38

What is driving GHG emissions?

Answer 38

Human-induced climate change indicators
i) Air pollution has increased atmospheric CO2 (~30%) since 1800’s
+ population growth, urbanization, agriculture
 increase in other greenhouse gases CH4 & N2O
ii) anthropogenic release of CO2
(fossil fuel burning & industry)
iii) reduction in forestry
 less efficient recycling of CO2 by photosynthesis
iv) CO2 increase mirrors global economic growth
• Greenhouse gas concentrations have increased to levels unprecedented in 800 kyr
•Human-induced runaway greenhouse effect
 The Anthropocene

Question 39

Future climate change

Answer 39

• GCM’s (global circulation models)  prediction of future climate.
• Many model scenarios suggest a 2-3oC increase in global temp over the next 100 yrs. x10 faster than the warming of last 10 ka.
• The beginning of the next glaciation is highly unlikely in the next 120 kyr.
• High cumulative anthropogenic CO2 will cause ice-free conditions in the N Hemisphere throughout the next half a million years, postponing glacial inception up to 600 kyr after present or later.

Question 40

What are sunspots

Answer 40

-spots on the suns surface that are darker than the surrounding area which reduce surface temperatures on land and causing cooling

Question 41

What are ice sheet binge/purge

Answer 41

ice sheets may exhibit short periods of enhanced ice flow (the purge phase) followed by longer spells of much slower flow (the binge phase). This behavior is thought to be controlled by internal ice sheet dynamics and, hence, may occur under stable environmental conditions.