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October 9, 2007
We talked about proxies, evidence that has been mounted to support the claim that there have
been major changes. The strongest evidence comes from looking at the small changes in ratios
of oxygen. There are various isotopes that we looked at. Scientists looked at small changes of
temperatures and the amount of ice in the Antarctic and Greenland.
One key organism for about the last 65 years looks like this. They are called Foraminifera or
Forams. They have little strands that form and complete a dynamic web. There are 275,000 of
these species but each of them forms a ‘test’ which is the shell of the Foram. You find them in
the world’s oceans and other places and when they die they rain down to the floor of the ocean.
You have large concentrations of these and each can be identified as species. They are used as
bio-indicators. What the environment was and also temperature indicators. They incorporate
into their shell calcium carbonate CaCO3 and the critical bit is the oxygen. WE have known
about these tests up to 540 million years ago. So from the start of visible life on the planet we
have these guys sitting on the floors of the oceans telling us things. Scientists have isolated the
ones that are indicators. In the 1960’s you have research vessels that were deep sea drill units
that drilled into the floor of the oceans and brought up cores. Then they would bisect the cores to
try to understand the pattern and what they told us about the past. They got this information as a
by-product as they were originally interested in oil.
Going back to the oxygen 18 story, if you look at the ratio incorporated in things like Forams, the
ratio between 18 and 16 will tell you certain signatures. The ratio that is incorporated changes
depending on temperature of the water that they grow in. So a change of only about .2
parts/thousand tells them there is a 1C decline in the surrounding water. This is sufficient to
estimate the temperature of the water that the Forams grew in. The colder the water, if you think
that the oxygen 18 have 2 more neutrons, the colder the less the vibrational advantages oxygen
18 has. Under cold conditions oxygen 16 and 18 are taken up in a similar ratio. Less 16 is
incorporated in warm conditions than under cold conditions. So this is a signature of
temperature. They look at oxygen 18 in the calcite in the tests. There is a bit of a hook in that
this ratio is good only when there isn’t a lot of ice on the planet. Where there are not huge ice
sheets it is a good signature of temperature. AS the ice sheet increase oxygen 16 evaporates
more than 18 so there is a concentration of oxygen 18 in the world’s oceans. Now it tells you
that you are getting a more concentrated/enriched ocean environment. So it tells you how much
ice volume there is. How much total water on the planet is stored in ice sheets? You can get a
good signature of what the planet looks like and that is what they used.
BGYC58H3F.October,9, 2007 LECTURE 5 1
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Uses of Forams
Here shows the last 600 thousand years from the deep sea sediments (from the drill rigs). You
can see the changes of the isotopes in 16 and 18. We have been in an ice age. There is an
alternating growth and decline but there is no period without ice. These fluctuations indicate a
period where there is maximum ice (about every 100,000 years). We know that now we are
inter-glacial (warm) but no more than 18,000 years ago it was maximum and there were probably
about 2 – 3 kms of ice above this room. You get repeated ice sheets and then an inter-glacial and
they are nicely mapped. I will show a 65 million year period as well. This is referred to as the
pleistocene age. You can see about the last 4 to 5 hundred thousand years. At the start of the
pleistocene it was only about 41,000 so the cycle is very rapid. Having that much ice sitting in
the north and south poles and coming down to crush most of Canada has a huge effect on bio-
diversity. Who saw Ice Age? The movie was very good. Everyone had to migrate or they died.
This shows a longer window. Remember the dinosaurs are taken out at the boundary of 70 -> 65
and then the next point is called the tertiary. We have really no major ice sheets in this time. We
have a lot of water and then the oxygen 18 signal tells you what the temperature was like. So in
this case it is relative to right now. It shows things in respect to that in terms of global
temperature. When we had the dinosaurs it was 10C warmer than today. It was very warm and
it had to be because they were very large reptiles. I will show you later that carbon dioxide
levels change as well as other major forces in the earth. When the two plates collide you get the
Tibetan plateau and you get Mount Everest and all that. You can see the main uplift almost 30
million years later. The mountains stop weather and the Asian monsoons are a result of the
Tibetan uplift. They also cause major amounts of ice and snow. This is reflected in the
temperature profile. The C4 plants are also affected; they are a much more efficient way of
carrying up photosynthesis. They take up carbon dioxide and also concentrations of carbon
dioxide are higher. The spread of C4 and the uplift plateau helped to drive this down. It is just
one of the factors that are driving down temperature. So we went from a warm humid world to a
cold world and the Forams tell us that. Remember for the last 1.8 billion years the pleistocene is
made of the pleistocene and the Holocene.
How do we know that climate has changed?
We are talking about Biotic Palaeoclimatic proxies. They are not the only indicates about past
climate there are also Abiotic Palaeoclimatic proxies. The main are using oxygen 18 and bore
holes. When water condenses the heavier water molecules holding oxygen 18 condense and
precipitate first. In zones like the tropics that have high evaporation they have high amounts of
oxygen 18 and then as you move towards the north and south it becomes more and more
depleted of oxygen 18. If you look at Canada, winter is coming; the amount of oxygen 18 that
precipitates out of snow will be less than the rain that falls in Florida. Changes in the global
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climate alter the patterns of evaporation and precipitation. It will change the ratio between
oxygen 18 and 16. The same thing happens to the heavy isotope of hydrogen. It is also
evaporation and precipitation dependent. If you look at things like the heavy hydrogen, the
terrestrial ice sheets (Antarctica and Greenland) the concentration of heavier elements will reflect
the temperature difference of the water from which it evaporated and the air from which is froze.
You can look at the ice cores they have taken in Greenland and Antarctica and directly measure
the ratios as a signature of temperature.
Vostok Station (1957)
You can see pictures of the station. The critical station from the perspective of climate is the
Vostok Station in Russia. They divided up Antarctica. Underneath this portion 3 ½ metres
below is Lake Vostola which is a problem. They have drilled down through this over time and
they went very deep. The first one they got within about 500 metres of the lake and then they
decided not to go further. The last one went about 3300 metres down and that is the longest core
we have. The cores look like this when they come out (on overhead) and this one is a core from
Greenland (about 16,000 years old). You can see dust and holes that have carbon dioxide and
methane etc. My notes say the last drill went 3623 metres so you have about 600,000 years of
temperature profiles. This gives us a good idea of what happened. It is really important where
you drill because if you are at the height of land, the further you go down you will get
compression and distortion so you want to be where no flow occurs. Here on Mount Logan you
get major distortion because the water is moving. It has to be stable.
This shows the core for about the last 400,000 years. I want to emphasize the 2nd abiotic proxy
and it is using carbon dioxide and methane from these bore holes. These holes have bubbles of
air that are trapped as I mentioned so they should reflect atmospheric climate change. If you
think about it things like methane, when those concentrations go up in the world, they are
produced in wetlands (bogs) and that is where you get methane formation. So if there is methane
in the cores it must be relatively warm. As methane drops it goes to a cooler environment.
You can see the carbon dioxide profile, the methane profile, the temperature deduced from those
and the bottom one is oxygen 18 changes and the very bottom one is the changes in sunlight
intensity. You can see the signature is shown in the 4 major glacier cycles. 1 per 100,000 years
is the one at the bottom.
S:What happens every 100,000 years?
T:Glacier cycle – full glaciations to inter-glacial which is what we are at now. It is very
warm. Maximum glaciation is 18,000 that started about 100,000 years ago.
BGYC58H3F.October,9, 2007 LECTURE 5 3
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