Marine isotope stages

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 MARINE ISOTOPE STAGES

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 . What are Marine Isotope Stages?

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. What's MIS (contd.)

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. What is Oxygen Isotope Fractionation?

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 – 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. Oxygen Isotope Fractionation

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

7. OIF : Various Processes 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 .

8. 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. OIF : Various Processes

9. What are Glacial and Non-Glacial Periods ? 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.

10. Glacial and Non Glacial Periods (contd.) 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.

11. 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. Understanding and Measuring Isotope Stages

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