The study of past climates is important to gain an understanding of the range of natural climatic variability prior to human influences. This knowledge can help to develop more accurate computer models to predict future climate changes. Most instrumental climate records, however, only go back about 150 years, so scientists look to nature to find additional information about past climates.
One way researchers do this is to recover and analyze ice cores, which represent accumulations of snowfall over time. Ice core researchers examine different chemical compositions in layers in the ice. Deeper ice core layers represent times farther in the past. A chemical composition that has not changed over time due to compression or other variables can indicate certain past atmospheric conditions. The concentrations of particular chemicals in ice cores over time can help scientists infer what past climates might have been like.
Graphing Ice Core Data*
*dates are plus or minus one year
Scientists were able to date this ice core with the help of some outside knowledge: They knew that the Tambora volcano erupted in 1815. Estimating that it took the volcanic sulfate about one to two years to reach Antarctica, scientists could then identify 1816-1817 from the first elevated (above normal) sulfate levels in the ice core. From that point, and using information about how certain chemical concentrations are connected to spring and fall, the dates for the rest of the core can be estimated. The volcanic sulfate from the unknown 1808-1809 eruption arrived in 1810-1811, as evidenced by the second set of elevated sulfate levels.
Sodium and chloride concentrations correspond closely because they come from the same source—seawater. Elevated chloride concentrations during the volcanic events are likely a result of hydrogen chloride released during a volcanic eruption. Slightly elevated chloride concentrations in the non-volcanic years (1812 to 1816 and again in 1820) may be due to higher atmospheric hydrogen chloride that is present during summer months.
Peaks for winter and spring can be seen each year with peaks in sulfate (spring/summer) and sodium chloride (winter/spring); sometimes the seasons appear concurrently in the ice core because there is not a high enough sampling resolution. Southern Hemisphere winter occurs from June to August; spring occurs from December to February. Core dating is not an exact science; the estimates given are plus or minus one year. The total range for this data set is 1811-1821.
Mayewski, Paul, and Frank White.
The Ice Chronicles.
NOVA's Web Site—Mountain of Ice
What Is Paleoclimatology?
Stories in the Ice
The "Secrets in the Ice" activity aligns with the following National Science Education Standards and Principles and Standards for School Mathematics.
Structure of the Earth system
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