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.

inte

r-g

laci

al

inte

r-g

laci

al

inte

r-g

laci

al

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