Page 348 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

312 part II The Water, Weather, and Climate Systems
▲Figure 11.6 Changing concentrations of 16O (light oxygen) and 18O (heavy oxygen) in water vapour between equator and North Pole. [Modified from illustration by robert Simmon, naSa gSFC.]
35 000 samples for research- ers (see www.oceandrilling.org/ ). The international program in- cludes two drilling ships: The U.S. JOIDES Resolution, in oper- ation since 1985 (Figure 11.8b), and Japan’s Chikyu, operating since 2007. Chikyu set a new record in 2012 for the deep- est hole drilled into the ocean floor—2466 m—and is capable of drilling 10000 m below sea level and yielding undisturbed core samples. Recent improve- ments in both isotope analysis techniques and the quality of ocean core samples have led to improved resolution of climate records for the past 70 million years (see Figure 11.10).
Ice Cores In the cold regions of the world, snow accumu- lates seasonally in layers, and in regions where snow is per- manent on the landscape, these layers of snow eventually form glacial ice (Figure 11.9a). Sci- entists have extracted cores of such glacial ice to reconstruct
Specialized drilling ships have powerful rotary drills able to bore into ocean-bottom rock and sediment, ex- tracting a cylinder of material—a core sample—within a hollow metal pipe. Such a core may contain dust, miner- als, and fossils that have accumulated in layers over long periods of time on the ocean floor (Figure 11.8a).
The Integrated Ocean Drilling Program completed about 2000 cores in the ocean floor, yielding more than
climate. The world’s largest accumulations of glacial ice occur in Greenland and Antarctica. Scientists have ex- tracted cores drilled thousands of metres deep into the thickest part of these ice sheets to provide a shorter but more detailed record of climate than ocean sediment cores, presently pushing the record back 800000 years.
Extracted from areas where the ice is undisturbed, ice cores are about 13 cm (5 in.) in diameter and are
“Light” oxygen in water vapour moves poleward
18O
“Light” oxygen reservoir forms in glaciers and ice sheets
16O Glacier
“Light” oxygen in
water vapour moves
poleward 16O
16O, 18O
“Light” and “heavy” oxygen isotope ratio is in balance
(b)
Interglacial
▲Figure 11.7 relative oceanic concentrations of 16O and 18O during colder (glacial) and warmer (interglacial) periods. [Based on Analysis of Vostok Ice Core Data, global Change, available at www.globalchange.umich.edu/globalchange1/current/labs/lab10_Vostok/Vostok.htm.]
“Heavy” oxygen remains in ocean water
(a)
Glacial
Near the poles, atmospheric water vapour is increasingly enriched in 16O
Heavy, 18O-rich water vapour condenses over mid-latitudes
Water, slightly enriched in 16O, evaporates from warm subtropical waters