Paleo Slide Set: Polar Ice Cores
ECM variations based on data from a 2.4 m section of ice from approximately 100 m below the surface.

This figure shows how ECM varies annually and how this signal can be used to date the core. Remember 
that ECM is a way of gauging ice acidity. Dust from Arctic Canada and Greenland is alkaline, so 
precipitation deposited on the ice sheet during dusty periods is less acidic than precipitation deposited 
at other times. Dusty Arctic summers show up as lower readings in the ECM record. Scientists correlate large 
ECM peaks with historical records of volcanic eruptions. The 1660 eruption of Katla in Iceland and the 1667 
eruption of Japan's Tarumani appear in this core segment. The volcanic signal in the ECM record greatly improves 
dating accuracy by providing absolute dates, unambiguous benchmarks upon which a reliable core chronology depends. 
ECM and other parameters that vary seasonally such as dust concentration, d18O, and visual stratigraphy have been 
used to date the core to 40,000 yr B.P. with an estimated age error of 10%; currently, age models are being used 
to provisionally date the deepest core, and work is continuing to extend this dating to even greater depths. 

Photo Credits:
Kendrick Taylor 
DRI, University of Nevada-Reno