Lab: Vostok Ice Core

Map showing Antarctica and location of Vostok Ice Core. Colors indicate elevation.

I. Introduction

Snow falling in the polar regions of the earth (e.g. Greenland and Antarctica) sometimes is preserved as annual layers within the ice sheets, provided that they are not destroyed by flow of the ice. These annual layers provide a record of the earth's climate that reaches back as much as 200,000 years.

Several different climate indicators can be measured from samples of the ice:

The Vostok core was drilled in East Antarctica, at the Soviet station Vostok from an altitude of 3488 m, and has a total length of 2083 m. Ice samples have been analyzed with respect to isotopic content in 2H, dust, and methane and carbon dioxide trapped in air bubbles. The profiles of 2H, methane, and carbon dioxide concentrations behave in a similar way with respect to depth in the core, showing a short interglacial stage, the Holocene, at the top, a long glacial stage below, and the last interglacial stage near the bottom of the core. The record goes back in time about 160,000 years.

For more information on these topics, read the through this lab on the University of Michigan website: http://www.globalchange.umich.edu/gctext/Inquiries/Inquiries_by_Unit/Unit_8a.htm.

Remember that this is just another resource- the questions asked there are not the same as what we are asking you!

II. Lab Instructions

A. Gas Age vs. Ice Age

Age is calculated in two different ways within an ice core. The ice age is calculated from an analysis of annual layers in the top part of the core, and using an ice flow model for the bottom part. The gas age data accounts for the fact that gas is only trapped in the ice at a depth well below the surface where the pores close up.

Task 1: Transfer the Vostok ice core data to Excel, and save it as an Excel workbook. Plot both the ice age and the gas age as a function of depth on the same graph. Describe the graph and answer the following questions:What are the units of both age scales?

B. δD as a proxy for temperature

Task 2: Next you will calculate the temperature based on the isotopic composition of the ice. Insert a blank column into the table to the right of the delta-deuterium column (δD). Isotopic ratios are used to model temperature. Calculate the temperature at Vostok based on the following formula describing the empirical relationship between temperature and deuterium concentration:

Temperature (deg-C) = -55.5 + (δD + 440) / 6

*Be sure to save your work!*

Now plot your calculated temperature vs. ice age. How reliable do you consider this paleoclimate record to be? (Hint: think about some of the uncertainties in the age models and compare the age of the Last Glacial Maximum (LGM) to what scientists consider the age to be today.) How long ago did the maximum temperature occur? How long ago did the minimum temperature occur? How do these temperature compare to the current temperature at current average Vostok temperature?

C. CO2, CH4, and Dust

Task 3: Plot CO2 as a function of gas age. How closely does the plot of CO2 resemble that of temperature? Now plot CO2 against temperature. Add a trendline and record the R2 value. Based on your work in previous labs, do you think this correlation is significant?

Task 4: Make the same plots for CH4. Is CO2 or CH4 more closely correlated with temperature? Why do you think that is?

Now make a plot of dust as a function of ice age. Compare this to the temperature plot; how well do the changes in dust concentration correlate with the temperature changes?

Task 5: The present atmospheric CO2 and CH4 concentrations are 375 ppmv and 1,700 ppbv, respectively, according to IPCC (2001). Calculate the changes in CO2 and CH4 concentrations between the last glacial maximum and the 18th century, and between the 18th century and today. Why were CO2, CH4, and dust concentrations different during the glacial time as compared to the 18th century?

Task 6: Insert today's CO2 concentration (use the IPCC value given above) into the linear regression equation from question #4 to determine what the past relationship between CO2 and temperature predicts that today's temperature should be at Vostok. How does your calculation compare with the known value?

D. Trends

You can calculate the rate of change of temperature (degrees/ka) by subtracting one temperature from the next oldest and dividing by the ice-age difference. That is:

(younger temp - older temp)/(older ice age - younger ice age) = rate of change (positive for warming, negative for cooling)

Recall that younger means shallower here.

Task 7: Calculate the warming rate for the entire time series and plot warming rate vs. ice age. What is the most rapid warming that occurred during the deglaciation that began around 15,000-20,000 years ago? How do the rates of warming that you've calculated compare with the current temperature data?

Task 8: Now calculate the rate of change in greenhouse gas concentrations (CO2 and CH4) versus gas age for this time period. How do these rates of change compare with the change in carbon dioxide and methane concentrations that has occurred over the past 100 years?

Task 9: Note that there were two major warming events representing two deglaciations in the Vostok calculated temperature data. Then look at how CO2 and CH4 change during those deglaciation periods. From the data provided in this lab, can you tell which changes first, temperature or greenhouse gas (CO2, CH4) concentrations? Why is this important?

III. Lab Report Instructions

Write a lab report (as per the Lab Report Format) summarizing the major findings of your investigation. In addition, address the following questions:

  1. How did conditions during the last glacial maximum (around 20,000 years ago) differ from today's conditions?
  2. How do the glacial/interglacial changes in temperature, carbon dioxide, and methane compare to the changes since the 18th century?
  3. Why are these ice core paleoclimate records so important to our understanding and prediction of climate change?

IV. Contributor

J. Chapellaz, Laboratoire de Glaciologie et Geophysique de l'Environment, Grenoble

V. Optional Reading List

Excel Help - If you are unfamiliar with Excel, work through these Excel help pages.

Created by Stephanie Pfirman, Barnard College and the Columbia/Barnard Earth’s Environmental Systems: Climate team.

Updated October 2, 2007
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