GEOL 1330 Lab #6 Global Warming

GEOL 1330 

Global Warming

Lab #6  

1. (10 points) Explain what isotope fractionation means, using the example of evaporation. As a result of this process, how is the isotopic composition of water frozen in ice sheets different from ocean water?

2. (40 points) One way to study El Niño in past centuries is to measure the oxygen isotopic values in corals. The chart below shows a δ18O coral record from Urvina Bay, Galapagos Islands, 00° 24.52' S, 91° 14.04' W, for the years 1854-1981.

Find this location on a map of the Pacific. Why is it well suited to study past El Niño events?

For review, what is the relationship between sea temperature and δ18O values?

With this in mind, note 3 years of especially warm temperatures (possible El Niños) and 3 years of especially cold temperatures (possible La Niñas) recorded in the coral.

Warm years:

Cold years:

Based on previous studies, a 1 ‰ change in δ18O values corresponds to 4°C change in temperature. For the Urvina Bay record, during what years does the largest change in temperature (over a 2 year period or less) take place? And how much did the sea water temperature change over this period?

There also appears to be a significant change in Urvina Bay temperatures during the most recent part of the record (1961-1981). Explain the character of this change.

3. (50 points) The ODP (Ocean Drilling Program) core 677 was retrieved from the eastern tropical Pacific from a water depth of 3450 m.

The chart below shows a marine δ18O record from benthic (bottom-living) foraminifera from ODP core 677. The horizontal axis is shown in kyr before present.

What is the approximate range through which δ18O values fluctuate between 2 million and 1 million years ago? And between 500 kyr ago and the present?

What does your previous answer indicate about the relative magnitude of the change in global ice volume during these two intervals?

Based on this δ18O record, intervals of greatest ice volume and least ice volume have been identified. Intervals of greatest ice volume are termed glaciations, whereas intervals of least ice volume are termed interglaciations. Because the marine δ18O is so useful for understanding ice volume changes, climate scientists have designated isotope stages, with odd-number stages representing interglaciations and even-number stages representing glaciations. The duration of stages is given in the table below. According to this table, when was the last glaciation? How long did it last?

The graph below shows the δ18O record of the past 500 kyr from ODP 677. Draw vertical lines on this graph to represent the boundaries between the isotope stages.

Which four isotope stages shown above/on your graph display the greatest ice volume?

During what stages do the four lowest δ18O values on the curve over the past 500 kyr occur?

Teamwork in the lab is encouraged. However, each student must provide his/her own answer. Copying of answers results in a grade of zero for all students involved.