Page 350 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

314 part II The Water, Weather, and Climate Systems
(a) A scientist stands in a snowpit at the West Antarctic Ice Sheet, where layers of snow and ice revealing individual snowfall events are backlit by a neighbouring snowpit.
(b) Scientists inspect an ice-core segment at Dome C. A quarter-section of each ice core is kept on site in case an accident occurs during transport to labs in Europe.
▲Figure 11.9 Ice-core analysis. [(a) NASA LIMA. (b) and (c) British Antarctic Survey. (d) Bobbé Christopherson.]
chapter, includes a discussion of methane hydrates and their potential impacts on present-day warming.)
During the PETM, the rise in atmo- spheric carbon probably happened over a period of about 20000 years or less— a “sudden” increase in terms of the vast scale of geologic time. Today’s accelerating
Warmer (less ice)
Cooler (more ice)
(c) Light shines through a thin section from the ice core, revealing air bubbles trapped within the ice.
–1.0 0.0 1.0 2.0 3.0 4.0 5.0
(d) Air bubbles in the glacial ice indicate the composition of past atmospheres.
PETM
(a)
70 60 50 40 30 20 10 0 Millions of years ago
(b)
3.0 4.0 5.0
5.0 4.5
Warmer (less ice)
Cooler (more ice)
4.0 3.5
3.0 2.5 2.0 Millions of years ago
15 1.0
0.5 0.0
▲Figure 11.10 Climate reconstructions using oxygen isotopes (18O) over two time scales. The vertical axis (y-axis) shows the change in 18O parts per thousand, indicating warmer and colder periods over the past 70 million years (top graph) and the past 5 million years (bottom graph). (a) Note the brief, distinct rise in temperature about 56 million years ago during the Paleocene-Eocene Thermal Maximum (PETM).
(b) The bottom graph shows alternating periods of warmer and colder temperatures within the 5 million year time span. [After Edward Aguado and James Burt, Understanding Weather and Climate, 6th edition, © 2013 by Pearson Education, Inc. Reprinted and electronically reproduced by permission of Pearson Education, Inc., Upper Saddle River, New Jersey.]
Change in 18O (parts per thousand)
Change in 18O (parts per thousand)