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

Journal of Geophysical Research, Vol. 102, No. C12, p. 26,747-26,754, 1997

J.P. Steffensen, H. B. Clausen, C.U. Hammer
Departement of Geophysics, The Niels Bohr Institute of Astronomy, Physics and Geophysics, University of Copenhagen.
M. Legrand, M. De Angelis
Laboratoire de Glaciologie et de Geophysique de l'Environnement, Centre National de la Recherche Scientifique St. Martin d'Héres, France.
R. Alley
Earth system Science Center and Department of Geosciences, Pennsylvania State University University Park.
H. Shoji
Kitami Institute of Technology, Kitama, Japan.

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 stratigraphy is still a matter of debate [Chapellaz 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, event 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 profiiles. 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 explannation.