What this lesson teaches
I can use ice and ocean cores to explain how climate varied during the Quaternary.
Syllabus 8834, Topic 1.2, 1. The Science of Climate Change. Is climate variability a new phenomenon in Earth's history?
Make a guess
Tiny air bubbles trapped in ancient ice are analysed. What do the bubbles themselves record?
- The air temperature on the day they formed.
- Samples of old air, with its carbon dioxide.
- Nothing useful, because the air has escaped.
- The exact year the ice fell as snow above it.
Show the answer
Samples of old air, with its carbon dioxide.
Bubbles trap old air, so they show past gas levels. Temperature comes from isotope ratios in the ice, which act as a proxy.
Ice and ocean cores hold indirect clues to past climate, and comparing dated records shows repeated warming and cooling.
The Quaternary is the period from about 2.6 million years ago to today. The Pleistocene had repeated glacial periods, with more land ice, and warmer interglacials. The Holocene began about 11,700 years ago. These labels do not mean the whole planet was frozen or ice-free.
A proxy is indirect evidence of something that was not measured directly. In ice cores, the ratios of oxygen and hydrogen isotopes in the ice help show past temperatures. Tiny air bubbles trap samples of old air, including carbon dioxide. Dust and other particles add more evidence about past environments.
Ocean cores hold layers of mud and tiny fossil shells. The mix of species shows past conditions. Oxygen isotopes in foraminifera, small shelled organisms, reflect both water temperature and how much water was locked in ice. So the signal needs calibrating against other evidence.
Layers must be dated before records can be compared. Air is sealed in later than the snow fell, so ages can differ. When independent records agree, the conclusion is stronger. Mixed sediment, dating errors and changing build-up rates blur the timing, so one core is not a complete record of global temperature.
Climate variability means changes in average climate and extremes over time, not single weather events. It can come from internal processes or from natural and human influences. Cores show climate varied long before industry, but cannot alone explain today's warming. To explain today's warming, compare the timing, size and physical effects of present natural and human influences.
- Quaternary
- About 2.6 million years ago to today.
- Holocene
- Began about 11,700 years ago.
- Proxy
- Indirect evidence, like isotopes or trapped air.
Step by step
Date the record
Find the layers and estimate their age.
Read the proxy
Link isotopes, fossils or gases to what they show.
Compare evidence
Check other sites and proxies before a global conclusion.
Worked example: Two measurements from one ice core
Temperature comes from isotopes in the ice, and carbon dioxide from trapped air. When both move together, it supports a climate-carbon link. Dating shows which changed first.
Watch out for this
Air bubbles in ice directly record past air temperature.
Bubbles preserve old gases. Temperature is inferred from the ice's isotopes.
Check your understanding
Why should an ocean-core oxygen isotope record be checked against other evidence?
- Each layer is exactly one year, so the dates need checking.
- Its signal reflects both water temperature and ice volume.
- It contains little climate information on its own.
Show the answer
Its signal reflects both water temperature and ice volume.
Yes. Two influences are mixed, so other evidence helps separate them.