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

Old ice for palacoenvironmental studies retrieved by deep core drilling in the central regions of the large ice sheets can also be retreived from the ice-sheet margins. The δ ¹⁸O 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 δ ¹⁸O records reaching back to the Pleistocene. Many of the characteristics δ ¹⁸O variations known from Greenland deep ice cores can be recognized, allowing an approximate time-scale to be established along the ice-margin records. A flowline model is used to determine the location on the ice sheet where the margin ice was originally deposited as snow. The Pleistocene-Holocene δ ¹⁸O change at the deposition sites is determined by comparing the δ ¹⁸O values in the ice-margin record to the present δ ¹⁸O values of the surface snow at the deposition sites. On the northern slope of the Greenland ice sheet, the Pleistocene-Holocene δ ¹⁸O change is about 10‰ in contrast to a change of 6-7‰ at locations near the central ice divide. This is in accordance with deep ice-core results. We conclude that δ ¹⁸O 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.