Comparison between Greenland ice-margin and ice-core oxygen-18 records

Old ice for paleoenvironmental studies retrieved by deep core drilling in the central regions of the big ice sheets can also be retrieved from the ice-sheet margins. The d18O-content of the surface ice was studied at 15 different Greenland ice-margin locations. At some locations, two or more records were obtained along closely spaced parallel sampling profiles, showing good reproducibility of the records. We present ice-margin d18O- records reaching back into the Pleistocene. Many of the characteristic d18O-variations known from Greenland deep ice-cores can be recognized, allowing an approximate time scale to be established along the ice-margin records. A flow line model is used to determine the location on the ice sheet where the margin-ice was originally deposited as snow. The Pleistocene-Holocene d18O-change at the deposition sites is determined by comparing the d18O-values in the ice-margin record to the present _18O-values of the surface snow at the deposition sites. On the northern slope of the Greenland ice sheet, the Pleistocene-Holocene d18O-change is c. 10 per mil in contrast to a change of 6-7 per mil at locations near the central ice divide. This is in accordance with deep ice-core results.We conclude that d18O-records measured on ice from the Greenland ice-sheet margin provide useful information about past climate and dynamics of the ice sheet, and thus are important (and cheap) supplements to deep ice core records