analyses that can provide information on changes in past temperature, the water cycle, and the carbon cycle. You will work with speleothem data from South America in Chapter 3.
1 The best speleothems for paleoclimate reconstruction form when cave conditions are just right – like Goldilocks needed her porridge just right. Think about how stalagmites form on the floor of a cave:If conditions were too wet (e.g. if the cave was flooded with groundwater), how would that affect the ability of a stalagmite to form?If conditions were too dry, where no groundwater is dripping into the cave through fractures in the ceiling, how would that affect the ability of a stalagmite to form?How would evaporation conditions differ near the entrance to a cave compared to farther back in a cave? Which of these two settings would provide a more ideal location to obtain a speleothem for paleoclimate reconstruction?
2 What would a layer of hardened mud in a stalagmite imply about the environmental history of the cave? (In other words, how could the mud have gotten there?)
3 Go to the supplemental resources to watch videos and read a short article on selecting and collecting a speleothem for paleoclimate research. Make a list of the challenges of obtaining speleothems for paleoclimate research and the strategies scientists use to overcome these challenges.ChallengesSolutions
4 Like tree‐rings, radiometric dating (in this case, U‐Th isotopic dating, which you can explore more in Chapter 3) can be used to determine the age of the speleothem layers. However, unlike tree‐rings, the layers in speleothems are not necessarily annual layers. Their accumulation rate depends on the rate of water dripping into the cave.What could you infer about regional precipitation if you see that the younger layers in a stalagmite increase in thickness?Would you expect all caves globally to show the same changes in layer thickness through time? Why or why not?
Glacial Ice
1 Where does glacial ice (i.e. glaciers or ice sheets) exist today?
2 Go to the supplemental resources to watch videos and read a short article on the ice core drilling process. Make a list of the challenges of obtaining ice cores for paleoclimate research and the strategies scientists use to overcome these challenges.ChallengesSolutions
FIGURE 1.6. Piece of an Antarctic ice core showing trapped air bubbles.
(Source: Photo credit: Oregon State University, media release 9‐11‐08, http://oregonstate.edu/dept/ncs/newsarch/2008/Sep08/icecore.html).
Bubbles of ancient air (Figure 1.6) found in glacial ice are unique and valuable indicators of past climate. Unlike most other climate indicators, which indirectly record climate parameters, the trapped air in glacial ice is a direct measure of atmospheric gases (e.g. CO2 and CH4) of the past. As snow recrystallizes into ice below the surface of a glacier, air is trapped in the pore spaces between ice crystals. The pore spaces are eventually closed off from the atmosphere by continued accumulation of new snow, and by the recrystallization and fusing of individual ice crystals from layers of snow to firn (compacted snow) to ice. Because the pore spaces are open to the atmosphere until the ice forms, the age of the gases in the pore spaces is younger than the age of the surrounding ice. Trapped gas comprises 10–15% of the volume of glacial ice at the “bubble close‐off depth” (i.e., the depth of the firn–ice transition) (Bender et al., 1997).
1 Is the age of the trapped gas older than, younger than, or the same age as the ice that is trapping it?
2 Examine Figure 1.7, which shows a lab where ice cores samples are analyzed, and read the following brief description of the sample preparation and gas analysis process:Ice samples were cut with a bandsaw in a cold room (at about −15 °C) as close as possible to the center of the core in order to avoid surface contamination. Gas extraction and measurements were performed by crushing the ice sample (~40 g) under vacuum in a stainless‐steel container without melting it, expanding the gas released during the crushing in a pre‐evacuated sampling loop, and analyzing the CO2 concentrations by gas chromatography. The analytical system, except for the stainless‐steel container in which the ice was crushed, was calibrated for each ice sample measurement with a standard mixture of CO2 in nitrogen and oxygen. (text modified from: http://cdiac.ornl.gov/trends/co2/vostok.html)Identify some specific conditions and methods from the above description and propose why these are necessary to produce accurate and precise gas concentration data from the ice core:FIGURE 1.7. Class 100 Clean Room at Byrd Polar and Climate Research Center. Class 100 means there are less than 100 particles (diameter > 0.5 μm) per cubic foot of air.(Source: Photo from: http://bprc.osu.edu/Icecore/facilities.html#AnalyticalFacilities).
3 There are hundreds of analytical labs around the world that are capable of measuring CO2 and CH4 gas concentrations from ice core samples. How could investigators ensure that the results from different labs are comparable?
4 In 1992, the European Greenland Ice Core Project (GRIP) drilled down 3029 m to the base of the Greenland Ice Sheet at Summit, Greenland (72°N, 38°W). A year later, the U.S. Greenland Ice Sheet Project 2 (GISP2) completed drilling of a companion record through the ice sheet 30 km to the west. What value might there be in obtaining two parallel ice core records so close together?
5 The upper 2788 m of the GRIP ice core contains a Greenland paleoclimate record of the last 110 000 yr. The European Project for Ice Coring in Antarctica (EPICA) recovered the deepest and oldest ice record to date at Dome C, Antarctica. This 3270.2 m‐long ice core contains a paleoclimate record of the last 740 000 yr.Calculate the average ice accumulation rates (cm/yr) for the GRIP and EPICA ice cores. Show your work, including the conversion from meters to centimeters.Which has a higher average ice accumulation rate: GRIP or EPICA? Circle your answer.Which record spans a greater period of Earth history: GRIP or EPICA? Circle your answer.Which has a higher average resolution: GRIP or EPICA? Explain your reasoning.
Coring Marine Paleoclimate Archives
Corals
Corals are colonial animals that primarily live in clear, shallow, warm waters of the tropical ocean. The animals themselves are small polyps with flower‐like tentacles that move with the currents to catch plankton. Corals also receive nutrients from photosynthetic algae that live within their tissue. Individual coral polyps secrete crystals of aragonite, a form of calcium carbonate (CaCO3), which makes a hard external skeleton that is shared by the colony. This is like a shared apartment building for thousands of individual coral polyps. The skeletal structure grows as coral polyps build upon the existing structure that earlier generations secreted. Annual growth patterns can be recognized in climate‐related seasonal variations in the density of the skeletal material. These density differences show up easily on X‐ray images of corals (Figure 1.1d).
The skeletal structure of living and dead corals extends the record of climate change from modern
