Page 49 - Earth's Climate Past and Future

CHAPTER 2 • Climate Archives, Data, and Models 25

Youngest
layers Youngest
varves

Oldest Glacial Ice Oldest
varves
layers
Bedrock Rock

A Annual ice layers B Annual sediment varves

Youngest
bands

Youngest rings

Oldest
bands
Oldest rings
Coral reef

C Annual tree rings D Annual coral bands
FIGURE 2-9 Annual layering Four kinds of climate archives have annually deposited layers
that can be used to date the climate records they contain: (A) ice, (B) varved lake sediments, (C)
trees, and (D) corals.

protected regions. Determining the actual age of these rate at which the record is buried beneath additional
sequences by counting varves back in time from the sediments and protected from further disturbances.
present is impossible because varves were not con- Sediment Archives Most sedimentary archives used
tinuously deposited up until the present. However, the for climate studies form in low-energy marine environ-
varves supply an internal chronometer with which to ments undisturbed by turbulent waves and storms. The
count the years that elapsed during the interval when primary disturbance after particles settle out on the
they were deposited. This information can aid climatic seafloor is physical stirring by deep-dwelling organisms
interpretations. (Figure 2–10). Organisms living on the sediment surface
thoroughly mix the uppermost layers. A much smaller
number of animals burrow deep into the sediments, but
2-3 Climatic Resolution
they do so only infrequently, and subsurface sediments
The extent to which the details of climatic information are increasingly protected from most disturbances as
can be resolved depends mainly on the interplay between they are buried. Eventually the sediments pass beneath
two factors: (1) the processes that initially disturb the cli- the region of active mixing and become part of the
mate record during and soon after deposition and (2) the permanent sedimentary record.