Quaternary Period Flashcards

Question

Dating techniques: absolute, radiometric incremental, relative

Answer 1

•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)

Answer 2

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

Answer 3

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

Answer 4

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

Answer 5

• Oxygen Isotope Chronostratigraphy • Tephrochronology • Palaeomagnetism • Palaeosols

Answer 6

• 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?

Answer 7

• 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

Answer 8

- 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

Answer 9

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

Answer 10

• 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)

Answer 11

• 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.

Answer 12

• 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).

Answer 13

• 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

Answer 14

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

Answer 15

• 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.

Answer 16

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

Answer 17

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.

Quaternary Period Flashcards

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