1. EARTH AND CLIMATE
MARINE ISOTOPE STAGES
Time scale showing paleoclimate of past 300,000 years, derived from foraminifera
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2. EARTH AND CLIMATE
CONTENTS
Introduction
Principle
Sampling Method & Analysis technique
Formula used
Classification scheme of MIS
Discussion
Bibliography
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3. EARTH AND CLIMATE
INTRODUCTION
Palaeoclimatologists use stratigraphic records of stable isotopes of to interpret
palaeoclimates.
Marine isotope stages (MIS) were developed by successive & collaborative work of
Harold Urey, Cesare Emiliani, John Imbrie, Nicholas J. Shackleton, N. D. Opdyke,
J. Van Donk & many others.
Climatic signals are recognizable due to slight differences in geochemical behavior of
isotopes of Nitrogen, Oxygen, & Sulfur at the interfaces of cryosphere, hydrosphere
& atmosphere
Oxygen isotope stages (OIS) are used as a proxy for polar ice mass, as polar ice
sheets wax & wane, changes happen in the ocean’s isotopic composition, which is
ultimately etched into the CaCO3 shells of diatoms, foraminifera, & conodonts.
Oxygen & Sulfur isotopes, have a residence time of ~ 3200 yrs & ~ 10 million yrs in
the open ocean, respectively.
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4. EARTH AND CLIMATE
Some applications of sulfur isotopes 34
S & 32
S :
1) Understanding sulphur cycle from the late Miocene onwards using gypsum
2) To establish links between anthropogenic activities & climatic change.
3) In future it will allow us to confirm/dispute the presence of alien life in
extraterrestrial samples.
PRINCIPLE
When seawater evaporates, lighter isotope of oxygen, 16
O, is preferred over heavier
isotope of oxygen, 18
O. This process is termed fractionation.
Over time, evaporation & condensation (precipitation) can amplify this by
distillation, making oceans rich in 18
O & polar ice caps rich in 16
O.
18
O :16
O Ration is 1:500 under normal condtions
e.g. During Devensian glaciation, deep-ocean waters were enriched in 18
O by 1.6%.
This is equivalent to a ~ 165 m drop in sea levels.
SAMPLING METHOD & ANALYSIS TECHNIQUES
MIS are obtained by drilling & coring onboard ocean research vessels, e.g. ORV Sagar
Nidhi, JOIDES Resolution.
These core samples are transported to labs on land where they are analysed by
gaseous mass spectrometry.
Mass spectrometry requires the sample to be converted into a gas (e.g., CO2, O2).
Inside the spectrometer, the sample is vaporised in a vacuum, ionised into atoms, &
then passed first through a strongly accelerating electric field & then through a
powerful magnetic field, which gives a measure of the atomic & molecular masses.
FORMULA USED
δ18
Ois calculated using the following formula
Note - The isotope ratios are expressed as deviations from a standard, in permil
(permil are equal to ten times the value of percent).
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5. EARTH AND CLIMATE
CLASSIFICATION SCHEME OF MIS
The classification scheme of MIS begins with the Holocene Epoch;
Interglacials stages are given odd numbers & glacial episodes are giver even
numbers. The list continues up to MIS 104, beginning 2.614 million years ago.
MIS Began (years
ago)
Climate Major events
1 11,600 Warmer Younger Dryas ended & Holocene epoch began;
Humans arrived in North America; Agriculture allowed Civilizations to
settle; Domestication of Horses;
2 24,600 Colder Last Glacial Maximum (sea levels were ~ 120 m below present levels) ;
The Sahara desert formed; Neanderthals disappeared ; Great lakes
formed from glacial meltwater ;
3 60,000 Warmer Humans reach South Asia; Laschamp excursion - geomagnetic event
occurred; A meteorite crater formed in Arizona;
4 74,000 Colder Toba Supervolcano eruption;
Pleistocene megafaunal extinction began;
5 1,30,000 Warmer Mitochondrial Eve lived; Humans left Africa;
6 1,90,000 Colder Humans appear in East & South Africa; Neanderthals built underground
edifices out of broken Stalagmites ;
7 2,44,000 Warmer Rise of Homo sapiens;
8 3,01,000 Colder UK became an island ;
9 3,34,000 Warmer Obsidian used in stone tools;
10 3,64,000 Colder Homo erectus in Siberia;
11 4,27,000 Warmer This stage is the most similar to MIS 1;
Oldest Human DNA ; Rise of Neanderthals;
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6. EARTH AND CLIMATE
Summary of major monsoon-controlled events during the past 500 ka.
(Dark and white shades represent higher than & lower than normal monsoon resp.)
DISCUSSION
Climate proxies like, OIS from lake sediments can give elevation data through time.
Note - isotope ratios from lakes are biased toward higher elevation areas within a
watershed. Palaeosols are found to be much better elevation proxies.
Ice cores from polar ice caps reveal composition of the atmosphere in the past.
" Beyond EPICA" is the latest ongoing project, it’s expected to reveal greenhouse gas
records as old as 1.5 million years, surpassing the 0.74 million yr record of the
previous EPICA expedition.
EPICA stands for (European Project for Ice Coring in Antarctica)
It will let the present generation of palaeoclimatologists to enhance & verify the
work of their predecessors.
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7. EARTH AND CLIMATE
(Horizontal bars denote average conditions; vertical ones are climate boundaries)
The changes in dominant cycles are not explained by Milankovitch Theory
Glacial periods are colder, dustier, and generally drier than interglacial periods
BIBLIOGRAPHY
1. http://dx.doi.org/10.1016/j.quascirev.2015.01.012
2. https://www.iaea.org/sites/default/files/publications/magazines/bulletin/
bull32-4/32406880915.pdf
3. https://earthobservatory.nasa.gov/features/Paleoclimatology_OxygenBalance
4. https://www.geologybites.com/carmie-garzione
5. The Sea Floor - An Introduction to Marine Geology 4th
Edition.
6. A Dictionary of Geology and Earth Sciences 4th
Edition.
7. Landscapes & Landforms of India, Part I - Past and the Present Climate of India
8. The Geologic Time Scale 2012, Chapter 9 & 10.
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