Ice core data (IMAGE) University of Washington Caption Ice core data show concentrations of nitrate (top line), hydrogen ions (middle line) and nitrogen-15 (bottom line) from 1772 through 2006. Credit Lei Geng/University of Washington Usage Restrictions News use only License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.