Lithium in Greenland ice cores measured by ion chromatography 

Annals of Glaciology, 35, p. 243-249, 2002 

M.-L. Siggaard-Andersen and H. Fischer
Alfred Wegener Institute for Polar and Marine Research, Columbusstrasse, P.O. Box 120161, D-27515 Bremerhaven, Germany.
J.P. Steffensen
Geofysisk Afdeling, Niels Bohr Instituttet for Astronomi, Fysik og Geofysik, Københavns Universitet

ABSTRACT.
Ion chromatography (IC) is a widely used technique for analyzing ice cores for ions like Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺, F^-, MSA^-, Cl^-, NO₂^- and SO₄^2- that are present in polar ice cores at ppb level. By using sample preconcentration and an optimized separation technique, we have been able to detect Li⁺ in ice-core samples in concentrations as low as 0.0001 μeq kg^-1 or 0.7 ppt by IC. During routine analysis of ions in ice cores, the lithium content has been evaluated and recorded. The IC technique used in these measurements and some exemplary IC data from the Greenland Icecore Project (GRIP) and the North Greenland Icecore Project (NorthGRIP) ice cores are presented. By these data we introduce Li⁺ concentration as a new parameter in the analysis of ice cores. Like other ions, Li⁺ reflects climatic changes and shows seasonal cycles. On the basis of the geochemistry of lithium, we suggest that Li⁺ measured in the Greenland ice ores is derived from mineral dust. However, data from the NorthGRIP ice core representing the 8.2 kyr BP Holocene cold event show a strong Li⁺ signal that does not correlate with any other ionic component measured. This means that the lithium content in ice cores is a signal with its own pattern, which is not yet understood.