Quaternary glaciations and landscapes

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What is the Quaternary period and how long does it span?

The last 2.6 million years (Pleistocene and Holocene), dominated by glacial-interglacial cycles with at least 104 climate stages

What characterises the pattern of glacial-interglacial cycles in the Quaternary?

Periods of rapid warming into interglacials followed by long, slow cooling into glacials. Early Quaternary cycles were high frequency/low magnitude; post-800ka cycles shifted to lower frequency/higher magnitude

What is the Mid-Pleistocene Transition?

A shift around 800,000 years ago when the dominant periodicity of glacial-interglacial cycles changed from 41,000 years (obliquity-driven) to 100,000 years (eccentricity-driven), with intensification of glaciation

What is a forcing function in climate science?

A mechanism that causes a climate system to change from its equilibrium state, driven by perturbations in the Earth-atmosphere system. Can be external (extra-terrestrial) or internal (Earth processes)

What are the three Milankovitch orbital parameters and their periodicities?

Eccentricity (~100,000 and 400,000 years) — change in orbit shape; Obliquity (~41,000 years) — change in axial tilt (21.8°–24.4°); Precession (~23,000 and 19,000 years) — wobble of Earth on its axis

What is the core premise of the Milankovitch/Croll astronomical theory?

Changes in the intensity of seasons in the Northern Hemisphere control ice sheet inception and decay. Cool NH summers are key — if summer is cold enough, winter snow does not fully melt and glaciers grow

What triggered the long-term Cenozoic cooling that set up our current glacial climate (~60 million years ago)?

Large-scale tectonic uplift (changing topography and atmospheric circulation), increased weathering rates removing CO₂ from the atmosphere, and modified atmospheric circulation patterns

What role did the Himalaya/Tibetan Plateau play in Quaternary glaciation?

Tectonic uplift changed the wave structure of airstreams in the upper atmosphere, cooling the Northern Hemisphere and contributing to glacial inception around 2.6 Ma BP

What is the oxygen isotope ratio (δ¹⁸O) and what does it record?

The ratio of heavy ¹⁸O to light ¹⁶O in ocean water or ice. It records ice volume changes — during glacials, ¹⁶O is locked in ice sheets making ocean water isotopically heavier (enriched in ¹⁸O); during interglacials, meltwater returns ¹⁶O to the ocean

What are Marine Isotope Stages (MIS)?

A Quaternary climate stratigraphy based on δ¹⁸O records from ocean sediment cores. Even numbers = cold (glacial) stages; odd numbers = warm (interglacial) stages

Why is the deep sea record considered the best palaeoclimate archive?

It has a low, regular sediment accumulation rate and negligible erosion, providing the longest and best-preserved continuous palaeoclimate record

What proxy data are found in deep sea sediment cores?

Biogenic sediments from calcareous planktonic organisms (recording isotopic balance, water temperature and salinity), relative abundance and morphology of species, and ice-rafted debris (IRD) recording ice sheet fluctuations

What can ice cores tell us about past climate?

Palaeotemperature (δ¹⁸O), atmospheric greenhouse gas concentrations (CO₂, CH₄ in trapped bubbles), past dust and aeolian activity, volcanic eruptions (sulphur, tephra), and annual layers for dating

Name four famous ice cores used in palaeoclimate research.

Vostok (1985), EPICA (2000), Dye 3 (1981), Camp Century (1966)

What is the relationship between CO₂, CH₄ and temperature shown in ice cores?

Strong correspondence — as greenhouse gas concentrations increase, temperature increases. This confirms the role of internal feedbacks in amplifying orbital forcing

What are sub-Milankovitch events?

High-frequency climate oscillations occurring within glacial-interglacial cycles at timescales of 10²–10³ years — shorter than Milankovitch periodicities. Includes Dansgaard-Oeschger cycles, Bond cycles and Heinrich events

What are Dansgaard-Oeschger (D-O) events?

~20 rapid climate oscillations during the last cold stage (80–20 ka BP) with a periodicity of 1,000–2,000 years. Characterised by abrupt warming of ~7°C followed by gradual cooling (sawtooth pattern). First discovered by Willi Dansgaard in the 1970s

What are Bond cycles?

Longer-term cooling cycles of 1,000–15,000 years during the last cold stage, comprising a long gradual cooling phase followed by abrupt warming. Heinrich events tend to coincide with the cold phase of Bond cycles

What are Heinrich events and what causes them?

Layers of ice-rafted debris (IRD) in North Atlantic marine sediment cores, recording massive iceberg discharge events. Linked to ice sheet binge/purge cycles (MacAyeal, 1992) and/or ocean warming triggering ice sheet instability (Bassis et al., 2017; Max et al., 2022)

What is the thermohaline circulation (THC) and why is it sensitive to freshwater input?

A global ocean conveyor belt driven by temperature and salinity density differences. Freshwater input (e.g. from melting icebergs) reduces salinity and density, preventing deep water formation and slowing/stopping the circulation — disrupting northward heat transport

How did Heinrich events influence the thermohaline circulation?

Massive iceberg discharge freshened the North Atlantic, reducing salinity and density, slowing NADW formation and THC — causing rapid cooling across the North Atlantic region

What caused the Younger Dryas cold episode (~13–11.5 ka BP)?

Freshwater outburst from Glacial Lake Agassiz into the North Atlantic via the St Lawrence River Valley, shutting down NADW formation and THC, triggering ice sheet regrowth and severe cooling. Ended abruptly with ~7°C warming

What caused the 8.2 ka cooling event?

Final drainage of Glacial Lake Agassiz via Hudson Bay into the Labrador Sea, causing rapid North Atlantic sea surface cooling — a clear signal of freshwater-forced THC slowdown during the early Holocene

What is the bolide impact hypothesis for the Younger Dryas (Firestone et al., 2007)?

A meteor/bolide impact in North America at 12.9 ka was proposed as the trigger, evidenced by a thin layer with magnetic grains, microspherules, charcoal, nanodiamonds and extraterrestrial helium at Clovis-age sites. Widely disputed due to lack of convincing evidence

What are the four main methods used to date glacial landforms and sediments?

Optically stimulated luminescence (OSL) — dates sediment burial; cosmogenic surface exposure dating — dates ice retreat; radiocarbon dating — dates organic material; varve counting — annually laminated lake sediments

What is the Last Glacial Maximum (LGM) and when did it occur?

The peak of the last glaciation, approximately 26,000–19,000 years ago, when ice sheets reached their greatest extent across North America, northwest Europe and other mid-to-high latitude regions

What is palaeo-glaciology and what evidence is used to reconstruct former ice sheets?

The reconstruction of former ice cover using: subglacial landforms (ice flow direction), moraines and meltwater features (ice margins), trimlines (ice thickness), and dating techniques

What are trimlines in glacial geomorphology?

Erosional tidemarks marking the upper limit of former glacier occupancy, identified by the contrast between ice-moulded bedrock below and weathered/shattered bedrock above

What is permafrost and how widespread is it?

Perennially frozen soil or bedrock forming where mean annual air temperature is below 0°C. Covers ~26% of Earth's surface. Continuous permafrost: MAAT −6 to −8°C; Discontinuous: MAAT −1 to −8°C

Name four periglacial landforms and their formation processes.

Patterned ground (sorted circles/stripes) — freeze-thaw convection

Pingos — growth of ice lens in former pond (MAAT −2 to −8°C)

Ice wedges — vertical ice growth in contraction cracks (MAAT −3 to −6°C)

Blockfields/felsenmeer — frost shattering

What are pluvial lakes and what do they indicate?

Lakes that formed during wetter climatic periods at low latitudes (e.g. Lake Bonneville, Mega-Chad). They indicate changes in moisture balance during the Quaternary — old shorelines mark periods of higher lake levels, often at the LGM due to lower temperatures and evaporation

What is the Holocene and what key climate events occurred within it?

The present interglacial (last ~11,500 years). Key events: Early Holocene Thermal Maximum (9–5 ka, 1–2°C warmer than present); 8.2 ka cooling event; Neoglacial cooling (4.5–2.5 ka); Medieval Warm Period (~750–1200 AD); Little Ice Age (~1500–1900 AD)

What was the Medieval Warm Period and what evidence supports it?

A warm period (~750–1200 AD) with temperatures 1–2°C above average. Evidence: Viking settlement of Greenland (~800–1000 AD), vineyards in southern Britain recorded in the Domesday Book (1086 AD). Spatial variability means it may not have been globally synchronous

What was the Little Ice Age (LIA) and when did it occur?

A cold period (~1500–1900 AD) with temperatures ~1–2°C below average, peaking around 1700 AD. Evidence: glacier expansion, southward migration of Arctic sea ice, Thames Frost Fairs. Matthews and Briffa (2005) define the core LIA as AD 1570–1900

What is the current state of anthropogenic climate change?

Since 1850: ~1.5°C warming, ~20cm sea level rise, CO₂ risen from 280ppm to ~430ppm. Anthropogenic emissions ~40 GtCO₂/yr. Last decade (2010–2020) was the warmest on record. Greenhouse gas concentrations are unprecedented in 800,000 years

When will the next glaciation occur according to Ganopolski (2016) and Talento and Ganopolski (2021)?

Under natural forcing, the current interglacial would last another ~50,000 years. Moderate anthropogenic CO₂ emissions (1,000–1,500 Gt) will delay the next glacial inception by at least 100,000 years; high cumulative CO₂ could postpone it by up to 600,000 years

What are the projected long-term consequences of current warming according to Clark et al. (2016)?

Near-total loss of the Antarctic and Greenland ice sheets over the next 10,000 years, resulting in 20–50 metres of global mean sea level rise across four emission scenarios