Paleo Slide Set: Low Latitude Ice Cores: High Resolution Records of Climatic Change and Variability 
in the Tropics and Subtropics
Visual Annual Layers of Core

Three deep core sections (from 122m, 130m, and 139m) show distinct annual bands produced by the 
deposition of dust during the dry season (dry season dust layers are represented by triangles). 
While annual bands provide accurate relative dating (the age of each ice band is known to be a year apart 
from directly adjacent bands), paleoclimatologists also search for absolute dates within a core chronology. 
The surface of the ice cap provides one absolute date. For example, the top layer of a core drilled in 1983 
is known to date from 1983; scientists can then date deeper layers relative to the surface. Scientists also 
attempt to locate absolute dates deeper in the core to improve the accuracy of the chronology. At Quelccaya, 
for instance, a thick layer of volcanic ash was found in a layer initially dated at 1598. Looking into historical 
records of colonial Peru, paleoclimatologists found that a massive eruption of the volcano Huaynaputina had 
occurred in 1600. Using the absolute date of 1600 for this layer, they were able to revise their chronology 
and improve its accuracy. Electrical conductivity measurements (ECM), particle concentrations, and the ratio 
of heavy to light oxygen molecules are other seasonally-variable core parameters that can be used along with 
visual stratigraphy in dating ice cores.

As the average thickness (l) of the annual layers in the slide demonstrates, annual layers thin significantly 
at depth due to increased pressure. While annual layers in the ice cliff shown earlier average 75 cm, annual 
layers at a depth of 139 m are just 4 cm thick and those at the core's base just 1 cm thick. 

Photo Credits:
Lonnie Thompson 
Byrd Polar Research Center, The Ohio State University