Long-term changes in the acid and salt concentrations of the Greenland Ice Core Project ice core from electrical stratigraphy

Continuous electrical records covering a climatic cycle are presented for the Greenland Ice Core Project deep ice core from Greenland. Electrical conductivity measurement (ECM) measures the acid content of the ice, and the dielectric profile (DEP) responds to acid, ammonium, and chloride. All features seen can be explained by chemical changes in the ice, and there is no evidence so far for any major change in electrical response with depth or age of the ice. Both records are dominated by the acidity of the ice which varies strongly from acidic in warm periods to alkaline in cold periods, controlled by neutralization by alkaline dust (calcareous and other mineral dust). When Ca is low, the acidity (mainly nitric acid) has a fairly constant background level throughout the cycle, with slightly lower values in ice believed to be from the last interglacial. Ca has to rise only slightly to neutralize the available acidity, so that acidity is a highly nonlinear reflection of climate changes. If neutralization occurred in the aerosol (rather than in the ice), then the number of cloud condensation nuclei over parts of the northern hemisphere could have been reduced, leading to reduced cloud albedo. This nonlinear feedback may have some importance for modeling of climate change. When both acid and ammonium levels are low, the DEP signal can be used to give a rapid indication of chloride trends

Microscopic observations of air hydrate inclusions in deep ice core samples

International Symposium on Physics of Ice Core Records. Shikotsukohan, Hokkaido, Japan, September 14-17, 1998

Impact of Local Insolation on Snow Metamorphism and Ice Core Records

Local insolation is a major component of the energy balance at the surface of an ice sheet and causes temperature gradient metamorphism (TGM) of snow and firn. TGM is one of the dominant processes changing the structure of dry snow. We present a physically based model that calculates insolation-induced relative changes in TGM in the past. The results indicate that TGM at Dome Fuji varied by up to a factor of 2 over the past 350ka, and is driven predominately by the precession-band variability in local summer solstice insolation. At Dome Fuji, the impact of glacial-interglacial temperature changes on TGM is almost fully compensated by synchronous, opposite changes in accumulation rate, which determines the exposure time of a snow layer to TGM. Even small remaining temperature signals in TGM can cause phase shifts between TGM and local summer solstice insolation of several ka. This directly affects the accuracy of orbitally tuned ice core time scales using O2/N2 or total air content records, as this dating method is based on the assumption of synchronicity between TGM and insolation. It must be assumed that the strong variability in TGM will also be reflected in physical and chemical ice core records by e.g. modulating the volatilization of reversibly deposited species including the stable isotopes of water. Sublimation and thus accumulation rates are also closely linked to TGM, affecting the concentrations also of irreversibly deposited non-volatile impurities. Thus, the effect of a local, post-depositional contribution of TGM on ice core records must be quantified prior to their interpretation in terms of larger scale climate variability in the orbital frequency bands.III. Firn densification, close-off and chronolog