The chemical composition of cold events within the Eemian section of the Greenland Ice Core Project ice core from Summit, Greenland

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Abstract
Selected segments from the Eemian period of the Greenland Ice Core Project (GRIP) core from Summit, Greenland, have been analyzed by ion chromatography and Coulter Multisizer. The results will be discussed with special emphasis on the sudden cooling events, event 1 and event 2, in the record as observed in the δ18O profile [GRIP members, 1993; Dansgaard et al., 1993]. Whether the sudden cooling events of the Eemian represent a real climatic signal or they are a consequence of disturbed ice core st ratigraphy is still a matter of debate [Chappellaz et al., this issue]. However, several features of the chemical profiles across these cooling events are difficult to explain if they were a result of disturbed stratigraphy. We will focus our discussion on the unique profiles of nitrate, methane sulfonic acid (MSA), and ammonium across event 1 and argue that even if we allow for movement of ions by diffusion or displacement of ions by physical or chemical interactions, events 1 and 2 are not likely to consist of ice from other climatic periods which have been inserted in the Eemian strata by folding processes. Furthermore, our records do not show any layers in the vicinity of the Eemian strata which can be a possible source of the ice in event 1. We believe that the events represent a climate signal, and we will discuss other possible explanations of the profiles. Our conclusion that the cold events in the Eemian represent a real climatic signal runs counter to other evidence from gas measurements. However, whatever their cause, the unusual chemical signals require further discussion and explanation.