Environmental Engineering Reference
In-Depth Information
continents not in today
s positions, and the ocean circula-
tion very different from that of today) there is an important
lesson for us. When the temperature goes up it can take a
long time for natural processes to bring it down again,
something that will be discussed later.
'
.
The Past
Years
There are good data on climate from the ice cores col-
lected by an international team at the Russian Vostok
scienti
c base in Antarctica. These Vostok ice cores let
us look at ice laid down earlier than any of the cores from
Greenland, for example. They were collected by core
drills that brought up miles of core samples and carefully
kept them cold for analysis. The Antarctic ice is laid down
in well-de
. Even at the
poles, snowfall is seasonal and the bubbles trapped in the
ice clearly mark the years. The layers can be counted to
date them, and if you want to see what is in the ice
from
ned layers as shown in
Figure
.
years ago, you have to count back through
layers. Fortunately, there are machines that
can do the counting.
fig. 4.1
Ice-core sample that shows annual banding. This photograph
shows a section of the GISP
meters in which
annual layers are clearly visible. The layers result from differences in
the size of snow crystals deposited in winter versus summer, and
resulting variations in the abundance and size of air bubbles trapped in
the ice. (Photo from Eric Cravens, Assistant Curator, National Ice
Core Laboratory. Credits: NSF, NICL.
http://www.ncdc.noaa.gov/
ice core from
-
