Glacial - Interglacial Cycles

early explanations to earths features

catastrophism

• James Ussher (17th century): Biblical chronology; world created 4004 BC.

• Diluvial theory: Geological features explained by Noah’s Flood

• John Woodward: Essay “Towards a Natural History of the Earth” – reinforced diluvial interpretation.

Diluvial Theory

earths surface features(eg. valleys, erratic boulders) were formed by. a single, massive flood often linked to the biblical flood

who introduced idea of sudden catastrophes shaping earth

George cuvier

• proposed that earth experienced abrupt revolutions (sudden, multiple local catastophes) which caused extinctions

how was cuviers theory linked to the flood

Robert Jameson translated his work and suggested the last “revolution” was the biblical Flood, promoting catastrophism.

(cuvier did not clear support single global flood)

what is catastrophism

A geological theory that Earth’s features were shaped by sudden, short-lived, violent events (catastrophes), such as floods or volcanic eruptions, rather than slow, gradual processes.

who turned the idea of catastophism into a global flood theory

william buckland who argued for a universal deluge(one massive flood covering whole earth) shaping earth

what problems did erratics pose for the diluvial theory

Because although floods were suggested as the cause, they could not convincingly explain how such large boulders were transported and deposited, making the theory weak

• ice rafts+ floods were the proposed transport mechanisms

what led to the decline of the diluvial theory

Evidence from glaciers (e.g., in Switzerland and Scandinavia) showed that ice movement—not floods—explained erratics, leading to glacial theory and the concept of the Ice Age.

What led to the development of glacial theory?

Evidence from Switzerland and Scandinavia showed that glaciers were once much more extensive, explaining erratics and moraines.

What did Ignaz Venetz propose in 1833?

That glaciers were much more extensive in the past, helping explain the presence of erratics and other glacial features.

• initial idea which contributed to formal development in 1837

who first presented evidence for widespread glaciation + when wastheory introduced

Louis Agassiz (1837): glaciers shaped landscapes

Evidence:

• Erratics (boulders transported by ice)

• Moraines (piles of glacial debris)

• Striations (scratches on rocks) → not formed by rivers.

• Studied Alpine landscapes and found similar evidence in NW Europe and N America.

• Publications: Étude sur les glaciers (1840), Système glaciaire (1847).

who introduced the term ‘ice age’

Karl Friedrich Schimper in 1837.

how did william buckland respond to the glacial theory

Initially unconvinced (1838), but after a field trip in 1840, he accepted glacial theory.

who supports glacial theory

Jean de Charpentier

What did Archibald Geikie discover in 1863?

He identified interglacial periods (warmer phases between Ice Ages), showing that multiple glaciations occurred rather than just one.

what did thomas chamberlin identify in 1882

4 major glaciations in North America

What did Albrecht Penck and Eduard Brückner establish?

4 major alpine glaciations (Gunz, mindel, riss, wurm)

why did scientists need new theories after discovering mutiple glaciations(multiple ice ages)

To explain large climate changes and repeated glacials/interglacials.

Why is land evidence for early ice ages limited?

Ice sheets discontinuous, dating hard, erosion removes older features, different materials complicate interpretation.

How did marine sediment cores change understanding of past ice ages?

They provide continuous, datable records of past climate, ice volume, and CO₂.

what was charles lyells explanation for climate change

Changes in land–sea distribution and uplift caused long-term cooling.

what did john tyndall propose

Small changes in water vapour and CO₂ could significantly affect climate.

what did Svante Arrhenius show?

changes in co2 levels could explain ice age temp changes

what did thomas chamberlin later propose about climate

A model where CO₂ changes (from oceans, weathering, etc.) drive glacial cycles.

what is the astronomical theory of ice ages

The idea that changes in Earth’s orbit and axis drive climate cycles.

What are the three main orbital components affecting climate?

• Eccentricity (shape of orbit)

• Obliquity (axial tilt)

• Precession (wobble of axis)

Which oxygen isotopes are used in paleoclimate studies and why?

¹⁶O and ¹⁸O; ¹⁸O is heavier and its ratio to ¹⁶O in shells varies with temperature and ice volume.

How do foraminifera record past climate?

They take oxygen from seawater to build CaCO₃ shells; the ¹⁸O/¹⁶O ratio reflects water temperature and ice volume.

• Colder water → more ¹⁸O in shells.(during ice ages large amounts o16 trapped in glacial ice)

• Warmer water → more ¹⁶O in shells.

How is δ¹⁸O calculated and what does it indicate?

mass spectrometry

δ18O=Rsample−Rstandardδ18O=Rsample​−Rstandard​; indicates past temperature and ice volume.

• Positive δ¹⁸O → colder water / more ice

• Negative δ¹⁸O → warmer water / less ice

who first recognized cycles in sea surface temperature using oxygen isotopes?

Cesare Emiliani (1987).

who refined the use of foraminifera oxygen isotopes

Nick Shackleton (1960s–1980s)

oxygen isotopes reflect both seawater temperature and global ice volume; higher δ¹⁸O indicates more ice and colder water.

oxygen isotope properties

• ¹⁶O – lightest, evaporates more easily.

• ¹⁸O – heavier, less likely to evaporate.

oxygen isotopes interglacial vs glacial conditions

interglacial: Ocean water evaporates → more ¹⁶O leaves the ocean.

• Most ¹⁶O returns as rain or river flow.

• Result: Ocean ¹⁸O/¹⁶O ratio stays roughly constant.

glacial: Large ice sheets form → ¹⁶O is trapped in snow and ice.

• Ocean water becomes relatively enriched in ¹⁸O.

• Organisms (e.g., foraminifera) incorporate this into their CaCO₃ shells → δ¹⁸O rises.

What period do the last 2.5 million years of glacial/interglacial cycles belong to?

Quaternary period (~2.58 Ma to present).

repeated glacial'/interglacial periods reflected in Marine sediment cores and δ¹⁸O ratios in foraminifera shells.

orbital forcing

the effect of small, regular changes in Earth’s orbit and tilt on the amount and distribution of solar energy (insolation) reaching the Earth. These changes alter climate over tens of thousands to hundreds of thousands of years.

milankovitch cycle

proposed theory describes the orbital parameters which cause the forcing

controls solar energy distribution, triggering glacial and interglacial periods.

orbital parameters (which make up the milankovitch cycle) affecting earths climate

eccentricity

obliquity

precession

precession of orbit

eccentricity

shape of earths orbit (ellipse <> circle)

• 100,000 year time scale(short term variation, dominant) + 400,000 year timescale (long term pattern)

• changes between 0 and 0.06

alters total solar radiation received

present day value of eccentricity

e = 0.01675

obliquity

changes in tilt of earths axis (22-24.5)

• 41,000 year timescale

changes seasonal contrast, affects intensity of summers/ winters especially at high latitudes

what is earths obliquity at present

23.5 degrees

high vs low obliquity

A high obliquity value reduces the difference in solar radiation received by high and low latitude regions of the Earth, while low obliquity results in more insolation at the equator, and less in the polar regions.

precession

wobble of earths axis

2 components: axial precession and apisdal precession

- determining at which point on the orbit the northern hemisphere winter (southern hemisphere summer) occurs

apsidal precession

The rotation of Earth’s elliptical orbit in its plane, moving the perihelion(point at which orbit closest to sun).

• Period ≈ 100,000 years

• alters timing of earths closest approach to the sun

present December closest to sun

5500 years ago September

axial precession

The wobble of Earth’s rotation axis caused by the Sun, Moon, and planets pulling on the Earth’s equatorial bulge.

• North Pole traces a clockwise circle in space

• Period ≈ 25,700 years

precessional parameter

describes the relationship between the seasons and Earth’s perihelion, determining when northern hemisphere winter or summer occurs

what is climatic precession of the equator of the equinoxes

The combination of axial and apsidal precession, producing cycles of ~23,000 and 19,000 years (mean ~21,000 years).

how does eccentricity affect precession

• When eccentricity = 0 → precession has no effect on solar radiation

• When eccentricity is high(stretched out) → precession amplifies climate effects

how does eccentricity affect insolation

Changes in eccentricity slightly alter the total annual insolation, but the effect is very small.

How do obliquity and precession affect insolation?

They redistribute solar energy seasonally and by latitude, but over a full year, the total insolation balances out to zero.

where is the effect of precession on insolation strongest

at the equator

who first suggested glaciation could occur when eath is further away from the sun

Hans Esmark (1827) — observed glacial evidence in Norway.

What did John Herschel propose about orbital changes?

1830 / 1832)

• Eccentricity alone too small to affect mean annual insolation

• Axial + apsidal precession could enhance seasonality, influencing climate

What was Joseph Adhémar’s idea in 1842?

• Ice ages alternate between hemispheres due to precession

• Southern winters longer by ~8 days at aphelion → more glaciation
  ❌ Incorrect: seasonal changes balance annually, so mean insolation doesn’t change

What were the key contributions of James Croll?

(1864–1875)

• Combined precession, eccentricity, obliquity in theory

• Winter = critical season for glaciation

• Ice age occurs when high eccentricity + winter at aphelion

• Emphasized positive feedbacks: ice albedo & ocean currents

• Predicted last Glacial Epoch 250–80 ka (later corrected)

What did Milutin Milankovitch contribute?

• Used eccentricity, obliquity, precession to calculate insolation at different latitudes

• Focused on summer insolation at 65°N for ice sheet changes

• Found: obliquity = high latitudes, precession = low latitudes

• Proposed synchronous global glaciations, amplified by northern ice sheets

• Became standard model for astronomical theory of Ice Ages

why does 65 degrees north latitude matter

Most of the large Northern Hemisphere ice sheets (e.g., Greenland, Canada) are located around 65°N latitude.

The amount of sunlight (insolation) they receive in summer determines whether snow accumulated in winter melts completely or survives to form ice.

Orbital changes (tilt + precession) affect summer sunlight at 65°N:

• Low summer insolation → less melting → ice sheets can grow over thousands of years → glacial period.

• High summer insolation → more melting → ice sheets shrink → interglacial period.

What are the periods of the three Milankovitch orbital cycles?

• Eccentricity: 100,000–400,000 years (small effect on annual insolation)

• Obliquity (tilt): 41,000 years (affects season strength at high latitudes)

• Precession (wobble): 19,000–23,000 years (timing of seasons, strongest at low latitudes)

INHG& Mid-Pliocene warm period

• INHG (Intensification of Northern Hemisphere Glaciation):

  • Transition from warm, stable mid-Pliocene (~3 Ma) → variable glacial/interglacial Pleistocene (~2.5 Ma–present).

• Mid-Pliocene is often considered a possible analog for future warming.

causes of great ice ages

3 requirements for northern hemisphere ice-sheet growth

1. Long-term cooling at high latitudes (>65°N) → ensures precipitation falls as snow.

2. Introduction of moisture → allows ice to accumulate.

3. Low summer insolation → prevents melting of winter snow.

• Orbital forcing triggers ice ages, internal climate feedbacks amplify the effect.

internal climate feedbacks

• Ice-albedo feedback

• Ocean circulation

• Atmospheric CO₂ levels

amplify small changes in insolation

seawater temp for ice growth

-1.8

what validate the milankovitch theory

1976 deep sea cores confirmed ice ages correlated w orbital parameters validating the theory

Why did James Croll suggest using deep-sea sediments to test the astronomical hypothesis?

Terrestrial records are fragmentary due to erosion and discontinuous deposition; deep-sea sediments could provide long, continuous records of glacial-interglacial changes.

Who first analysed continuous 1 m sediment cores and what did he find?

Wolfgang Schott (1935) — found variations in Globorotalia menardii indicating alternating cold and warm climates from the German Meteor expedition (1925–27).

What was the significance of the Kullenberg piston corer?

Allowed recovery of 10–15 m cores (longer, continuous records).

• Used in the Swedish Deep-Sea expedition of Albatross (1947–49)

• Gustaf Arrhenius analysed cores → cyclical CaCO3 variations linked to glacial-interglacial changes

• Introduced odd = warm, even = cold stage numbering (Holocene = 1)

Who expanded deep-sea core research in the 1950s?

Maurice Ewing at Lamont Geological Observatory

• Directed daily piston coring, reaching 200 cores/year

• Lamont collection became the largest in the world, critical for reconstructing past climate

• Ericson & Wollin (1956) used these cores to estimate SST variations from planktonic foraminifera

How did isotopes improve palaeoclimate reconstruction?

• Harold Urey (1946) proposed using Oxygen isotope fractionation (18O/16O) in CaCO3 to estimate temperature

• Cesare Emiliani (1955) applied it to planktonic foraminifera

  • SST varied ~6°C during glacial-interglacial cycles

  • Defined Marine Isotopic Stages (MIS) using Arrhenius notation

How did nicholas Shackleton refine isotope studies?

(1967)

• Analysed benthic foraminifera with improved mass spectrometer

• Showed d18O variations reflect ice volume, not just SST

• Confirmed oxygen isotope curves as global glacial-interglacial indicators

Why was equatorial Pacific core V28-238 important?

1973)

• Extended beyond Matuyama/Brunhes boundary (~700 ka)

• Shackleton & Opdyke: d18O record shows regular glacial-interglacial cycles to MIS 22

• Anchored chronology using MIS 19 = M/B boundary

How did Hays, Imbrie & Shackleton (1976) test the astronomical theory?

• Selected 2 high-accumulation sequences in southern Indian Ocean (last 450 ka)

• Measured d18O (ice volume) & seasurfacetemp from radiolarians

• Spectral analysis peaks:

  • 100 kyr → eccentricity

  • 42 kyr → obliquity

  • 23–19 kyr → precession

• Concluded: Earth’s orbital changes are fundamental cause of Quaternary ice ages