Post on 13-Jan-2016
Oxygen isotopes and climate
Secrets of the Sediments
ClimateThe long term average of temperature and
precipitation (30 years)
TodayInstruments collect data about temperature
and precipitation
Is our changing climate any different than past climate changes?
Should we be concerned?If it will impact our welfare
What was the temperature like in this environment?
This is a proxy.
A proxy is a substitute.
Did nature leave proxies for temperatures and
precipitation from the past?YES!
Tree Rings
Width of growth rings indicate temperature and moisture conditions.
Lake Varves
Thickness of light layers indicate deposition due to spring melting.
18O
Two types of oxygen
isotopes
16O
Water molecules differ
H H16O
H H18O
shell composition:
CaCO3
O-
H HO
Ca+
Foraminifera (forams)
C+
18O/16O
CaCO3
The shell is analyzed to determine the 18O/16O ratio.
Non-glacial period
H18O
H
H16O
H
H16O
H
H16O
H
H16O
H
H18O
H
H18O
H
H16O
H
(warm atmosphere)
Seashells are enriched with 16O (18O/16O is small)
Period of glaciation
H18O
H
H16O
H
H16O
H
H16O
H
H16O
H
H18O
H
H18O
H
H16O
H
Seashells enriched with 18O (18O/16O is larger)
(cold atmosphere)
glacier
Secrets of the Sediments
Task:To analyze sediments collected off the coast ofSanta Barbara to determine whether this information can be used to study historicalclimate change.
Let’s look at the results
Your graph should look like this
today past
4a. Look at the graph and describe what you see.
The highest ratio of 18O : 16O fluctuates over time.
today past
4b. During what three ages or time periods can youfind the highest 18O:16O ratios?
The highest 18O : 16O ratios are approximately 20,000 years ago, 65,000 years ago and 135,000 years ago.
ice age ice ageice age
today past
4c. Identify and list the time periods with the lowest 18O ratios.
The lowest 18O : 16O ratios are approximately today, 42,000 years ago and 125,000 years ago.
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r-g
laci
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r-g
laci
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laci
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today past
4d. Why do you think this pattern occurred? What might have been happening geologically? Climatologically?
Glaciers were melting and growing larger; the atmosphere was warming and cooling.
today past
4e. Predict and explain what will happen to 18O : 16Oratios as global warming continues.
18O:16O ratios will move closer to 1 : 1 as morewater melts from the ice caps and enters the oceans.
today past
4f. Do you think the levels of 18O can also indicatethe amount of ice found on land? Explain.
Yes. If there are high 18O:16O ratios, we can assume that there are larger amounts of iceon land, as the 16O would be “locked up” inthe glacial ice.
today past
Conclusion:
The 18O/16O ratio within foraminifer shells can be used to learn about past environments.
School of Rock
Joidesresolution.org
Oxygen isotopes and climate
Secrets of the Sediments
NESTA workshop Deep Earth Academy activity