You have been given a series of samples containing planktonic foraminifera representing time from the present to 150,000 years ago. You are processing the samples to look at the climatic signal they reveal in Earth’s recent history. You are aware that two particular species of foraminifera, Ammonia beccarii and Elphidium excavatum, are excellent recorders of water temperature through geologic time. Both species live in the shallow water, near-shore environment. When the Earth experiences periods of relatively cold temperatures, ocean waters are cooler and can retain more dissolved oxygen. These conditions favor the species Elphidium excavatum. Alternatively, during periods of relatively warm climatic periods, ocean waters heat up and are unable to retain as much dissolved oxygen. These conditions favor the species Ammonia beccarii. Therefore, you have separated each species from your samples to determine their A/E Index (Ammonia beccarii/Elphidium excavatum Index). Comparing the number of the two species found in each sample will provide the A/E Index by using the following formula:

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A/E Index = [#A/(#A+#E)] x 100

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where # = number of each species in the sample

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As ocean waters heat up, the A/E Index goes up; alternately, as ocean temperatures go down, so does the A/E Index.

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Procedure:

n1) You will need graph paper or use online graphing software to construct the graph for this exercise.nn2) For each time period sample you have counted the number of each species. Your data is recorded in Table 1. Your next step is to calculate the A/E Index for each sample. Complete the worksheet in Table 1 by using the equation provided. The first sample has been done for you.nn3) Use graph paper to plot your results. On the vertical axis you should plot the age of the samples with “0” at the top and “-150,000” at the bottom. On the horizontal axis, plot the A/E Index. You should now have a graph representing the climatic signal derived from the comparison of Ammonia beccarii to Elphidium excavatum populations.nn4) After completing your calculations and plotting your results, answer questions #4 and #5 found on the next several pages.nn