What are Marine Isotope Stages? How can MIS data be collected and what can we infer from them? Find out all about MIS in this presentation.

1. ARGHYA CHOWDHURY
5535

2.  Marine Isotope Stages (MIS) are alternating periods of
cool and warm climate on earth. These periodical data of
warm and cool climates are derived from Oxygen Isotope
Data collected from the sea at various time intervals.

3. The various marine isotope stages have been numbered
backwards from present ( MIS 1 – present ). Till date, over
100 stages have been identified.
To understand the concept of MIS, let’s first understand
Oxygen Isotopic Fractionation.

4.  In the various reservoirs of the earth, i.e. the hydrosphere,
atmosphere, the cryosphere and the lithosphere, there is presence of
Oxygen atoms.
 Now, there are two major oxygen isotopes that are present, 16O (8
neutrons) and 18O (10neutrons). 16O is the lighter isotope whereas
18O is the heavier isotope.

5.  The essential data is received from ratio of 18O and 16O, which is
also called Delta Notation.
∆ = 18O/16O
Let’s look at how the various earth processes can affect the delta value –
a) Evaporation : Evaporation of water vapour from the sea disturbs
the oxygen isotope ratio. Evaporation of the lighter isotope 16O is
much easier than heavy 18O.

6. Thus, 16O value gradually decreases in
the hydrosphere and increases
in atmosphere.
Therefore, during evaporation,
Hydrosphere  Delta increases
Atmosphere  Delta decreases

8.  b) Precipitation : Quite like evaporation, precipitation also favors an
O isotope. But, in this case, the heavier isotope 18O readily falls as
compared to the lighter isotope.

9. This eventually leads to an increase in 18O in the hydrosphere and
decrease in the atmosphere.
Thus, during precipitation,
Hydrosphere  Delta increases
Atmosphere  Delta decreases
c) Glaciation : The formation of ice-sheets and caps from freshwater is
called glaciations. During glaciations, a majority of 16O from the
water gets trapped in the ice sheets.
Thus, glaciation reduces the 16O further in the hydrosphere, leading
to further increase in delta value.

10. During Glacial
periods, seawater is
converted to ice
sheets. When this
happens, there is
reduction in 16O
in the
hydrosphere.
Thus, an increase
in delta value
indicates a
possible glacial
period.

11. Similarly, during non-glacial
periods, the surface ice sheets
melt and the water runs off back
into the sea and oceans
(hydrosphere). This 16O rich
water then again increases the
proportion of 16O in the
hydrosphere, thus reducing
the Delta value.
Thus, reduction in the ratio of
oxygen isotopes may indicate a
possible interglacial period.

12.  Scientists take sediment cores from the bottom of the ocean all over the
world and then measure the ratio of Oxygen 16 to Oxygen 18 in the
calcite shells of the foraminifera.
 Oxygen 16 is preferentially evaporated from the oceans, some of which
falls as snow on continents.
 Times when snow and glacial ice buildup occur therefore see a
corresponding enrichment of the oceans in Oxygen 18. Thus the
O18/O16 ratio changes over time, mostly as a function of the volume of
glacial ice on the planet.

15. a) Earth’s Climate by W F Rudiman
b) https://www.thoughtco.com/marine-isotope-stages-
climate-world-171568
c) https://www.sciencedirect.com/topics/earth-and-
planetary-sciences/marine-isotope-stage