Fig. 1.

Scattering on the higher dust concentrations that accompany cold periods increases the dust-logger signal in a profile of the clear ice at GISP2 (Upper), whereas absorption on dust decreases signal in the bubbly ice at Siple Dome (Lower). The GISP2 data have been smoothed for clarity; a few interstadials and the Younger Dryas (YD) are labeled. Volcanic signatures at Siple Dome are indicated with hashing; when magnified, each signal (here distorted in age space) is a distinctive asymmetric double spike (see, for example, the cusp near 71 ka).