From Isotopes to Temperature, & Influences of Orbital Forcing on Ice Core Records

created by Spruce Schoenemann, UW Earth and Space Sciences for the UW in the High School Climate Science Course.

Overview

This module provides a hands-on learning experience where students will review ice core isotope records to determine the isotope-temperature scaling and their relationship to orbital variations. The objective of this module is for students to learn how water isotopes are used to infer temperature changes back in time, and how orbital variations (Milankovitch forcing) control the multi-millennial scale climate variability. In addition, students will learn about how climate feedbacks (CO2, sea ice, iron-fertilization) can amplify/moderate temperature changes that cannot be explained solely by orbital forcing.

The module is divided into three independent parts, allowing teachers to pick and choose the sections they wish to cover when.

Overview of Entire Module, Labs 1,2, 3 and 4 (pdf)

Powerpoint Presentation (download) includes background information on stable isotope ratios, use of isotope analysis, and how to translate isotope values to temperature values.

Focus Questions

1. How do we infer temperatures from isotope data in an ice core?
2. What is the lapse rate and how does it work in the troposhere?
3. How does Rayleigh Distillation effect water isotopes in the hydrological cycle?
4. How do the three Orbital Parameters change the amount of incoming insolation?
5. What configuration of the Milankovitch Cycles is most likely to initiate a glaciation?
6. How does CO2 amplify or dampen the Earth’s temperature response?

Lab 1: From Isotopes to Temperature

The students will begin by finding ice core/snow pit locations in Antarctica and making predictions about how temperature might change with elevation and distance from the ocean. First they will determine the lapse rate (change in temperature with elevation) for the region. They will find the annual oxygen isotope data for the region and calculate the relationship between the isotopes and temperature. Next they will use the isotope-temperature scaling to determine the amount of temperature change at Vostok or Dome C. Each group/student can present their findings from their Antarctic ice core and the class can evaluate regional differences. In this lab, students practice calculating slopes and determining relationships between elevation, temperature, and isotopes.

Vostok (Lab Worksheet and Excel)

Dome C (Lab Worksheet and Excel)

Lab 3:Milankovitch Cycles as Primary Orbital Forcing for Temperature Variations

In this lab, students will use the Vostok ice core record, and online applet, to identify how orbital configurations (eccentricity, obliquity, and precession) initiate glaciations, as well as initiate deglaciations. The lab uses in interactive online website that allows students to select a number of time periods, and identify the insolation effects due to the exact orbital parameters during that same time period. The changes in insolation are then used to identify periods where the isotopes respond to reflect temperature increases or decreases.

Student Handout for Milankovitch Cycles

Lab 4: Orbital Driven Temperature Variations Amplified by CO2 Concentrations

In this lab students will investigate the contributions of insolation and CO2 radiative forcings responsible for the reconstructed temperature changes observed in the ice core records (Lab 2). The differences in orbital incoming radiation (i.e. insolation) between the glacial and interglacial periods can account for only about a fifth of the temperature changes recorded in the ice cores. This is because the orbital changes produce responses in other components of the climate system that amplify the changes. These include changes in the carbon cycle (CO2 feedback) and changes in the planetary albedo from more or less ice cover (ice-albedo feedback). Here, students will make basic calculations to determine the relative contribution of radiative forcing from orbital and CO2 differences between the glacial and present day.

Student Handout for CO2 Feedback

Student Excel for CO2 Feedback

 

Other Resources

Pre/Post Lab Survey

Answer keys are available upon request. Email uwpcc@uw.edu.

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