Passage IV

The study of oxygen isotopes present in water can give us clues to the climate of a certain location. The ratio of the isotopes ¹⁸O and ¹⁶O in a sample of rain, snow, or ice is compared to the ¹⁸O/¹⁶O ratio in a standard sample. A standard sample has a known value for the parameter being measured. The comparison of a sample’s ratio to that of the standard is called the O-18 index (δ¹⁸O) . The δ¹⁸O is calculated using the following formula:

Scientists conducted 3 studies to examine the δ¹⁸O of glacial ice in Arctic and Antarctic locations and learn about the past climates there.

Study 1

Containers were placed on glaciers at 25 locations in the Arctic to collect snowfall. The containers, contents were collected every 2 weeks during a 1-year period and analyzed for ¹⁶O and ¹⁸O. Figure 1 shows the calculated monthly δ¹⁸O and air temperature averages.

Study 2

At the 25 Arctic locations from Study 1, a 500 m deep vertical ice core was drilled. Each core represented the past 100,000 years of glacial ice accumulation at the site. Starting at the surface, samples were taken every 10 m along the length of the cores. These samples were analyzed for ¹⁸O and ¹⁶O. Larger δ¹⁸O values indicate that a relatively warmer climate existed at the time the ice was formed than do smaller δ¹⁸O values. The calculated average δ¹⁸O values for the samples are shown in Figure 2.

Study 3

The procedure of Study 2 were repeated at 25 Antarctic locations. The past 100,000 years of glacial ice accumulation at the site was represented by a 300 m ice core. The calculated average δ¹⁸O values for the samples are shown in Figure 3.