Oxygen isotopes and climate. The long term average of temperature and precipitation (30 years)
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Transcript of Oxygen isotopes and climate. The long term average of temperature and precipitation (30 years)
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Oxygen isotopes and climate
Secrets of the Sediments
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ClimateThe long term average of temperature and
precipitation (30 years)
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TodayInstruments collect data about temperature
and precipitation
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Is our changing climate any different than past climate changes?
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Should we be concerned?If it will impact our welfare
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What was the temperature like in this environment?
This is a proxy.
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A proxy is a substitute.
Did nature leave proxies for temperatures and
precipitation from the past?YES!
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Tree Rings
Width of growth rings indicate temperature and moisture conditions.
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Lake Varves
Thickness of light layers indicate deposition due to spring melting.
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18O
Two types of oxygen
isotopes
16O
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Water molecules differ
H H16O
H H18O
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shell composition:
CaCO3
O-
H HO
Ca+
Foraminifera (forams)
C+
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18O/16O
CaCO3
The shell is analyzed to determine the 18O/16O ratio.
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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)
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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
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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.
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Let’s look at the results
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Your graph should look like this
today past
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4a. Look at the graph and describe what you see.
The highest ratio of 18O : 16O fluctuates over time.
today past
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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
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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.
inte
r-g
laci
al
inte
r-g
laci
al
inte
r-g
laci
al
today past
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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
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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
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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
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Conclusion:
The 18O/16O ratio within foraminifer shells can be used to learn about past environments.
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School of Rock
Joidesresolution.org
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Oxygen isotopes and climate
Secrets of the Sediments
NESTA workshop Deep Earth Academy activity