Calibrating the Younger Dryas

Contributed by: Thom Davis, Greg Wiles, Roger Brown, David Bary

Key words: Radiocarbon dating, abrupt climate change, Younger Dryas, geochronology

Course Type: This exercise is designed for an upper level undergraduate course in Quaternary Studies.

Approximate time: Two hours

Description

This activity is a hands-on investigation involving the need for evaluating radiocarbon ages, the actual act of calibrating radiocarbon ages, and the application of these calibrated radiocarbon ages to the Younger Dryas (YD), an Abrupt Climate Change. The YD is a time of abrupt climate change with a number of controversial hypotheses for its origin.

Following brief lectures on the Younger Dryas and radiocarbon dating, students will do the following:

1. Research radiocarbon dating at the Beta Analytic website
   
2. Research the need for calibrating radiocarbon ages at the Wiki site for why calibration is needed
3. Calibrate a number of radiocarbon ages using CALIB Radiocarbon Calibration
   

Procedure

• Students generate 10 random radiocarbon ages from random.org within the time period of the Younger Dryas (between 10,000 and 11,000 C14 yr BP). For each radiocarbon age, generate the laboratory error using random.org (between 30 - 180 years; representing a mix of conventional and AMS ages). Enter data into a spreadsheet. An example of the generated ages can be found in this Carbon calibration worksheet (Excel 26kB Aug11 10).
• Work with CALIB 6.0 setting using 1 and 2 sigma and ages in years BP
• Calibrate each radiocarbon age and paste data into the spreadsheet

Questions about output:

• Make observations of the data generated from CALIB 6.0, such as:
  

1. How many of the radiocarbon ages yield multiple calibrated age ranges;
   
2. How does the calibrated age range vary for each radiocarbon age;
   
3. Are there any median probability ages that fall outside of the calibrated age ranges;
   
4. Pick one calibration image and describe the character of the curve through this interval.

• Overarching question: Based on your calibration of these ages comment on the challenges of dating changes during the Younger Dryas.

Goals

• Apply the basics of radiocarbon dating to the Younger Dryas
• Reinforce why radiocarbon calibration is done.
• Reinforce that radiocarbon ages are not dates and that ages are not exact points or one year in time, but rather ranges with probabilities
• Critically evaluate the difficulty of using radiocarbon ages through the Younger Dryas.

Assessment

• Successful generation of calibrated radiocarbon ages
• Informed discussion of the intricacies of applying calibrated radiocarbon ages to a specific time internal such as the Younger Dryas
  

References

GISP/GRIP ice core papers in Science on the YD as a rapid climate change event (RCCE)

Firestone, Kennett, et al. papers on the comet hypothesis for the YD

WGBH Nova film "The Last Extinction" (2009)