ENV100Y5 Lecture Notes - Lecture 48: Paleoclimatology, Atomic Number, Isotope Fractionation

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13 Feb 2016
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Lecture 48 – Stable Isotopes
Stable isotopes are used to study past climates
-Proxies tell us about past climates
-A proxy is a stand-in or a replacement; thus, it’s something that was present back then and that
mimicked some aspect of climate and recorded those changes naturally
-Glacial ice is the most powerful one
-Proxies has to record some aspect of climate; temperature, precipitation, etc; this is often
recorded in the composition of the material
-Anything that accumulates in seasonal layers, can potentially be used as a climate proxy, as long
as we have a way of attaching a date to those layers
-Glacial ice is a good candidate, because it’s controlled by climate and by how warm/cool it is or
how much snow is accumulating.
The composition of the ice is controlled by the temperature of the water from the ocean
Glacial ice accumulates in layers and we can attach dates to those layers
Snowfalls and snowflakes fall lightly to the ground and accumulate with lots of space in
between and that’s air; as the snow turns into glacial ice, it becomes more and more
compacted; even then, it can still have gaps and spaces, which are trapped air
Trapped bubbles are trapped ambient air and if we can tap into those bubbles, without
contaminating it with today’s bubbles air, then we can see the GHG concentration in that
air
-The isotopic analysis of ice corse is the most important source of paleoclimate data
Hydrogen has two different isotopes variants; one has extra neutron (deuterium) and the
one with two extra neutrons (tritium)
Oxygen has eight protons (that its atomic number)
O18 is the heavy isotope of Oxygen and the light one is O16
-H20 is water and can have light hydrogen or heavy hydrogen and light or heavy oxygen
-O18/O16 refers to the ratio of the heavy to the light oxygen in ocean water
-The masses of these are so big and it’s difficult to measure the difference between them
-It’s easier to distinguish between the heavy and the light, rather than the light and middle, or
middle and heavy
-If the 018 to 016 ratio goes up, it means heavier, but if it goes down, it means lighter (means it
has more of the light isotopes)
-The heavier water becomes more concentrated in the ocean water and the lighter water comes
together to form clouds
-We use all kinds of isotopes; some are better at distinguishing one process vs. another
-There are also natural isotopes as well
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