Stable isotopes as a proxy Flashcards
What are stable isotopes?
Isotopes that do not radioactively decay
Why and how do different isotopes behave differently?
Different weights make them behave differently. It takes more energy to move heavier atoms into a more distorted state e.g. from liquid to gas. It takes less energy to move a heavy atom into a less distorted state e.g. gas to liquid.
What is isotopic fractionation?
The favouring of the transfer of one isotope over another e.g. Oxygen 16 (16O) evaporates faster than Oxygen 18 (18O) because it is lighter. This changes the ratio between them.
What proxies do ice cores provide? What climatic interpretations can be made from them?
Thickness of annual layers and oxygen isotopes in ice. Thicker layers mean there was more precipitation that year, more 18O suggests a warmer climate.
What are oxygen’s two main isotopes? Which is the most common?
Oxygen 16 (16O) and Oxygen 18 (18O). Almost all of the oxygen on earth is 16O.
What is the fraction for oxygen isotopes?
18O/16O. Oxygen 18 is the numerator (positive), Oxygen 16 is the denominator (negative).
What can you measure the 18O of?
Anything containing oxygen e.g. ice cores, carbonate diatoms, foraminifera etc
How does having greater 18O stored in ice cores indicate a warmer/interglacial climate?
Warmer air can hold more moisture therefore in warmer periods more 18O is carried all the way to the Poles and precipitated there.
How does having greater 16O stored in ice cores indicate a colder/glacial climate?
Colder air cannot carry much moisture. Lots of 18O is lost though precipitation on the way to the Poles as it is the heavier isotope. The lighter 16O makes it to the Poles where it is precipitated and stored in ice.
Which carries more moisture, warm or cold air?
Warm air.
How does calcium carbonate shells having greater amounts of 16O identify interglacial periods?
Large amounts of 16O trapped in glaciers from colder periods will enter the sea when warmer periods melt the ice. Remains of organisms will reflect this 16O increase.
Why does calcium carbonate shells containing larger amounts of 18O indicate a glacial period?
Because more 18O will have been precipitated due to colder air and more 16O will be locked away in glaciers.
Name some advantages and disadvantages of using ocean cores as an archive.
They go back far back in time (further than ice cores, millions of years) and cannot be lost unless they are subducted, however they have a low resolution.
What are foraminifera?
Creatures that lived in oceans. They made shells out of calcium carbonate that contain oxygen which can be used to identify climates.
What proxies are found in ocean core archives?
Mg/Ca ratio (Magnesium to carbon ration), oxygen isotopes from foraminifera that lived in oceans.
