Abstracts of GRIP papers on chemistry and electrical studies

This file contains abstracts of GRIP papers whose primary content concerns chemistry (including volcanics, but excluding cosmogenic species) or electrical studies (including radar profiles). Papers are listed alphabetically by first author. You can go straight to the abstract you want.

Clausen, H.B., Hammer, C.U., Christensen, J., Schott Hvidberg, C., Dahl-Jensen, D., Legrand, M. & Steffensen, J.P. 1995. 1250 years of global volcanism as revealed by central Greenland ice cores. In Delmas, R.J., ed. Ice core studies of global biogeochemical cycles. Berlin etc.: Springer, 175-194.

Corresponding author: Henrik Clausen, Department of Geophysics, The Niels Bohr Institute of Astronomy, Physics and Geophysics, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen N, Denmark.

ECM profiles over the upper 297 m of the EUROCORE and GRIP ice cores, drilled at the Summit location in Central Greenland are presented. Special emphasis is given to the calibration of the ECM in terms of acidity and the chemical composition of the acids in the ice. The records reveal several acid signals caused by past volcanic eruptions over the period 740-1989 AD. The use of the ECM profiles as an indicator of volcanic acid deposition is discussed and the Summit record is compared to the record from Crete, 150 km south of the Summit region. Finally the ECM profile is discussed as an indicator of past upper atmospheric volcanic H2S04 load which is believed to be a key parameter for modelling the impact of past volcanism on past climate.

Clausen, H.B., Hammer, C.U., Hvidberg, C.S., DahlJensen, D., Steffensen, J.P., Kipfstuhl, J. & Legrand, M. 1997. A comparison of the volcanic records over the past 4000 years from the Greenland Ice Core Project and Dye 3 Greenland Ice Cores. Journal of Geophysical Research, 102, 26707-26723.

Corresponding author: Henrik Clausen, Department of Geophysics, The Niels Bohr Institute of Astronomy, Physics and Geophysics, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen N, Denmark.

Since 1980 the electrical conductivity method (ECM) has been used to infer volcanic acid signals in Greenland ice cores. The method reveals the great majority of major volcanic eruptions, including several known from historic records. Subsequent ion chromatographic analyses of the acid volcanic layers show the chemical composition, i.e., the concentration of the volcanic acids H2SO4, HCI, and HF plus, e.g., the nonvolcanically derived HNO3. While ECM data are available from a large number of shallow depth Greenland ice cores, covering the past 500-1500 years, only the Greenland Ice Core Project (GRIP), Greenland Ice Sheet Project 2 (GISP2), and Dye 3 deep ice cores exist for a detailed comparative study of volcanic signals in Greenland ice cores representing several thousand years. Comparison of the volcanic signals registered in the GRIP and GISP2 cores will be presented elsewhere. The latter cores were augered 30 km apart and essentially represent the same atmospheric conditions such as temperature, snow accumulation, and chemical composition of the air. Here we present a comparison between the major volcanic signals over the past 4000 years in the GRIP core from central Greenland and the Dye 3 core from SE Greenland in order to investigate the depositional differences. Many of the major signals are detected in both cores, but some of the differences in the records can be used to infer the latitudinal band of some eruption sites. Furthermore, the influence of the amount of annual precipitation and glaciological postdepositional processes on the volcanic signals is discussed.

Corazza, E. & Tesi, G. 1995. Tropospheric hydrogen and carbon oxides in Antarctica and Greenland. The Science of the Total Environment, 160/161, 803-809.

Corresponding author: Egizio Corazza, CNR, Istituto Geocronologia & Geochim isotop, Via Maffi 36, I-56100 Pisa, Italy.

Tropospheric trace gases (H2, CO, and CO2) were measured in polar areas for two seasons in Antarctica (Italian base Terra Nova Bay) and two in Greenland (European base Summit, Greenland Icecore Program [GRIP]), yielding the following average concentrations: Antarctica (1989-1990): H2, 528 ppbv; CO, 51 ppbv; CO2, 354 ppmv; Antarctica (1990-1991): H2, 522; CO, 51; Greenland (1991): H2, 548; CO, 114; Greenland (1992): CO, 107 (hydrogen discarded). Computer automated gas chromatographic analyses were done in situ using a reduction gas detector (RGD) and a complete set of standards each day, for periods of 2 h in Greenland and 3 h in Antarctica. Approximately 200 analyses were conducted during each campaign. Peak areas and standard calibrations in the laboratory were obtained using programs written especially for the purpose. For both Antarctica and Greenland, some differences were found between the two subsequent seasons; the greatest differences, however, were found in Antarctica within the same season (different origins of air masses). The inter-hemispheric asymmetry is clear and significant. It most likely occurs because pollution from the northern hemisphere reaches the northernmost regions through the polar vortex, whereas Antarctica is more isolatedby the Southern Ocean.

de Angelis, M. & Legrand, M. 1994. Origins and variations of fluoride in Greenland precipitation. Journal of Geophysical Research, 99, 1157-1172.

Corresponding author: Martine de Angelis, Laboratoire de Glaciologie et Geophysique de l'Environnement, B.P. 96, 38402 St. Martin d'Heres Cedex, France.

Summit-Greenland firn and ice core sections have been analyzed to determine the fluoride background level of high northern latitude precipitation and to investigate its temporal variations over various time periods. A continuous profile covering the last century and a discontinuous study of the last 27,000 years spanning the entire Holocene time period (0 to 11,500 years B.P.) and the late part of the last glaciation have been achieved. This first detailed study of the fluoride content of polar ice helps us obtain a better understanding of the atmospheric cycle of inorganic fluoride in remote atmospheres. First, our data suggest that blown dust is among the nonvolcanic sources that contributed to the natural fluoride background level of this high-latitude precipitation. Primary sea-salt emissions represent an insignificant contribution. Our study also indicates that high-latitude biomass burning debris which sometimes reaches the Greenland ice cap represents an additional weak source of fluoride for Greenland precipitation. Second, this work provides useful information for evaluating the impact of the volcanic activity on the fluoride budget of these high northern latitude regions. Indeed, our data demonstrate that although the natural background fluoride content of Greenland snow is very often sporadically disturbed by volcanic emissions from Iceland (numerous Hekla eruptions and the 1783 Laki eruption, for instance), located relatively close to the Greenland ice cap, large explosive eruptions (Tambora in 1815, for instance) only weakly disturb this background level. Our data suggest that even in the case of significant input within the stratosphere, fluoride is rapidly scavenged probably along with ash particles. Finally, our study of recent snow layers suggests that man-made sources (mainly coal burning) represent an important contribution which has dominated this high northern hemisphere fluoride budget for the three last decades. Furthermore, over the last 10 years, a possible influence of the stratospheric reservoir builded up from the chlorofluorocarbons' degradation cannot be ruled out and in the future this growing contribution may represent a significant part of the anthropogenic fluoride input compared to the input derived from coal burning.

DeAngelis, M., Steffensen, J.P., Legrand, M., Clausen, H. & Hammer, C. 1997. Primary aerosol (sea salt and soil dust) deposited in Greenland ice during the last climatic cycle: Comparison with east Antarctic records. Journal of Geophysical Research, 102, 26681-26698.

Corresponding author: Martine de Angelis, Laboratoire de Glaciologie et Geophysique de l'Environnement, B.P. 96, 38402 St. Martin d'Heres Cedex, France.

Ion chromatography data of Ca, Mg, Cl and Ca and Coulter(R) counter particle measurements are used to study the cycle of marine and continental primary aerosol reaching Greenland in relation to climatic changes over the last 150 kyr. A detailed comparison between Greenland (Dome Summit) and Antarctic (Vostok) records provides new insight on a potential link between northern and southern patterns. Ca is a good indicator of continental input and is mainly emitted as CaCO3. An attempt is made to estimate the contribution of aluminosilicates using the concentration of insoluble particles greater than 0.5 mu m in diameter. The relative abundance of non-sea-salt Mg and Ca and of aluminosilicate shows that the calcium content of continental background aerosol over Greenland was much higher during the glacial age. The neutralization capacity of carbonaceous aerosol is estimated. The inverse relationship between delta(18)O and continental input as well as the response of this input to the rapid climatic variations that have occurred during the second part of the glacial age are discussed in terms of source and transport modification in relation to the presence and the extent of the great Laurentide ice cap. The corresponding Vostok profiles strongly suggest that some of the phenomena observed at high northern latitudes are of global concern. The marine component of Na (Na-m) is a good tracer of sea-salt aerosol. Similarly to continental input, it shows an inverse but more linear relationship with delta(18)O. The sensitivity of Greenland and Antarctic marine input to climate variations of small and large amplitude is compared, and a corresponding estimation is made for the aeolian contribution. The respective influence of atmospheric circulation and the water vapor cycle is discussed. The chlorine to marine sodium weight ratio increases with temperature from values very close to the bulk seawater ratio during the last glacial maximum (18-20 kyr B.P.) to values significantly higher during the Holocene and warm Eemian. The corresponding excess of chloride (HCl) is discussed in terms of atmospheric transport, taking into account the role of atmospheric acidity on sea-salt fractionation processes. Owing to postdepositional phenomena, similar Vostok data must be considered cautiously. Nevertheless, aerosol fractionation seems to have been much more important over the Vostok site, except during glacial extrema.

Dibb, J.E. & Jaffrezo, J.L. 1997. Air-snow exchange investigations at Summit, Greenland: An overview. Journal of Geophysical Research, 102, 26795-26807.

Corresponding author: Jack Dibb, Glacier Research Group, Climate Change Research Center, Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Morse Hall, 39 College Road, Durham, NH 03824, USA.

The Greenland Ice Sheet Project 2 (GISP2) and Greenland Ice Core Project (GRIP) deep drilling programs at Summit, Greenland included support (both logistical and scientific) of extensive investigation of atmospheric transport and air-snow exchange processes of gases and particles relevant to the interpretation of the ice-core records. Much of the sampling for the air-snow exchange investigations was conducted at a unique solar-powered camp 30 km southwest of the GISP2 drill camp (even further from the GRIP camp) and was characterized by a high degree of international collaboration and cooperation. The wide range of expertise and analytical capabilities of the 20-plus investigators participating in these studies has provided important insight into the meteorological, physical, and chemical processes which interact to determine the composition of snow and firn at Summit. Evolving understanding of this system will allow improved reconstruction of the composition of the atmosphere over Greenland in the past from the detailed Summit ice-core records. This Paper provides an overview of air-snow exchange investigations at Summit, including their development through the course of the drilling programs (1989-1993), significant findings related to both air-snow exchange issues and the present state of the Arctic free troposphere, as well as the major outstanding questions which are being addressed in ongoing experiments at Summit.

Fuhrer, K., Neftel, A., Anklin, M. & Maggi, V. 1993. Continuous measurements of hydrogen peroxide, formaldehyde, calcium and ammonium concentrations along the new GRIP core from Summit, central Greenland. Atmospheric Environment, 27A, 1873-1880.

Corresponding author: Katrin Fuhrer, Physikalisches Institut, Universitat Bern, Sidlerstrasse 5, CH3012 Bern, Switzerland.

A new deep core drilling operation started in 1990 in central Greenland and in 1992 reached the bottom at a depth of 3028 m.b. surface. Taking advantage of recent developments in the analytical technique of chemical trace species, continuous high resolution measurements of H2O2, HCHO, NH4+ and Ca2+ concentrations were performed directly on the ice core in the field. During the 1991 season all four components were measured simultaneously between 1300 m.b. surface and 2300 m.b. surface, corresponding to the time interval between 8000 and 38,000 years B.P. In this paper an overview of the results and our first interpretations in terms of climatic changes are given.

Fuhrer, K., Neftel, A., Anklin, M., Staffelbach, T. & Legrand, M. 1996. High-resolution ammonium ice core record covering a complete glacial-interglacial cycle. Journal of Geophysical Research, 101, 4147-4164.

Corresponding author: Katrin Fuhrer, Physikalisches Institut, Universitat Bern, Sidlerstrasse 5, CH3012 Bern, Switzerland.

High-resolution ammonium measurements were performed along the Greenland Ice Core Program (GRIP) deep ice core, covering a complete climatic cycle. No overall anthropogenic increase is observed over the last 300 years; however, springtime concentrations have roughly doubled since 1950. Biomass burning is estimated to be a major source for ammonia emissions for preindustrial times. It contributes between 10% to 40% to the total ammonium deposited on the central Greenland ice sheet during the Holocene. No correlation is found between the ammonium summer concentrations recorded over the last 100 years and the area burned in northern North America, which is considered to be t main source axea for ammonium deposited on the central Greenland ice sheet. This suggests that the meteorological factor is predominant for the pattern of ammonium spikes observed in the ice core. If unchanged meteorological conditions are assumed for the Holocene, as indicated by the delta180 ice record, a decreasing biomass burning activity toward present time can be derived from the ammonium ice record. Soil and vegetation emissions axe responsible for the ammonium background concentrations in the ice. The record therefore may be used to trace back the biomass history of the North American continent. A pronounced decreasing trend in background ammonium is found during the Holocene, reflecting decreasing temperature and therefore lower NH3 emissions in the source region. Variations in the ammonium concentration during the glacial age are discussed in terms of changes in transport and deposition mechanisms and changes in source strength, which can be related to the extent of the Laurentide ice sheet. The data suggest that the Laurentide ice sheet was built up immediately after the last interglacial and went through several large fluctuations during the last ice age.

Fuhrer, K. & Legrand, M. 1997. Continental biogenic species in the Greenland Ice Core Project ice core: Tracing back the biomass history of the North American continent. Journal of Geophysical Research, 102, 26735-26745.

Corresponding author: Katrin Fuhrer, now at : II. Physikalisches Institut, University of Giessen, Heinrich-Buff-Ring 14, 35392 Giessen, Germany.

Ammonium, nitrate, and organic acid records from the Greenland Ice Core Project deep ice core are discussed. All species have a continental biogenic source that is situated predominantly on the North American continent for species deposited in Summit, central Greenland. The record therefore can be used to trace back the biomass history of the North American continent. Difficulty in the interpretation of these records arises from their unknown transfer behavior in a more alkaline atmosphere, which characterizes glacial time periods compared to interglacial stadials. This may have implications not only for weak acids such as formate and acetate, but also possibly for the transport and incorporation of HNO3 into aerosols, whereas ammonium is probably not affected by the alkalinity change of the atmosphere. Our approach is to compare samples with similar H+ concentrations throughout the record. From the records we infer several significant fluctuations in the extent of the Laurentide Ice Sheet during the last glaciation. We find evidence against the occurrence of an extensive Younger Dryas event in North America.

Gronvold, K., Oskarsson, N., Johnsen, S.J., Clausen, H.B., Hammer, C.U., Bond, G. & Bard, E. 1995. Ash layers from Iceland in the Greenland GRIP ice core correlated with oceanic and land sediments. Earth and Planetary Science Letters, 135, 149-155.

Corresponding author: Karl Gronvold, Nordic Volcanological Institute, Geoscience Building, University of Iceland, 101 Reykjavik, Iceland.

Four previously known ash layers (Ash Zones I and II, Saksunarvatn and the Settlement layer) all originating in Iceland, have been identified in the Central Greenland ice core GRIP. This correlation of the ash between the different environments is achieved by comparison of the chemical composition of glass shards from the ash. This establishes and confirms detailed correlations between the different types of depositional records and the absolute dating of the younger part of the ice core by counting annual layers dates the eruptions accurately. A precise connection with dates obtained by 14C beyond the range of dendrochronology is established which provides an excellent confirmation of 230Th-234U dates from corals. Four additional Icelandic ash layers have also been identified in the core but not yet correlated with known ash deposits.

Hempel, L. & Thyssen, F. 1992. Deep radio echo soundings in the vicinity of GRIP and GISP2 drill sites, Greenland. Polarforschung, 62, 11-16.

Corresponding author: Ludwig Hempel, (now at) Alfred-Wegener-Institut fur Polar- und Meeresforschung, Columbusstrasse, D-27568 Bremerhaven, Germany.

Surface based radio echo soundings with a specially designed burst system in the areas around the ice core drill sites GRIP and GISP2 in the central part of the Greenland ice sheet are presented. Digitally recorded and processed data sets show reflections from bedrock at ice thicknesses of more than 3 km and internal layerings in the ice sheet. The bedrock topography appears to be smoother in the close vicinity of the drill holes compared to more undulating bedrock in the south. The internal layerings show different behaviour above a bedrock trough between GRIP and GISP2 compared to most of the recorded data. The maximum ice thickness of 3400 m +/- 26 m is found 80 km south of GRIP.

Hong, S., Candelone, J.P. & Boutron, C.F. 1994. Greenland ice history of the pollution of the atmosphere of the northern hemisphere for lead during the last three millenia. Analusis, 22, M38-40.

Corresponding author: Sungmin Hong, Laboratoire de Glaciologie et Geophysique de l'Environnement, B.P. 96, 38402 St. Martin d'Heres Cedex, France.

The frozen atmospheric archives that are stored in the Greenland ice sheet have allowed us to reconstruct the history of the large-scale pollution of the atmosphere of the northern hemisphere for Pb since the Copper Age, when Pb was first produced as a by-product of Ag. Recently obtained data show that this pollution is the oldest ever reported; it was already significant during the Greek and Roman times more than two millenia before the Industrial Revolution.

Hong, S., Candelone, J.-P., Patterson, C.C. & Boutron, C.F. 1994. Greenland ice evidence of hemispheric lead pollution two millenia ago by Greek and Roman civilizations. Science, 265, 1841-1843.

Corresponding author: Sungmin Hong, Laboratoire de Glaciologie et Geophysique de l'Environnement, B.P. 96, 38402 St. Martin d'Heres Cedex, France.

Analysis of the Greenland ice core covering the period from 3000 to 500 years ago - the Greek, Roman, Medieval and Renaissance times - shows that lead is present at concentrations four times as great as natural values from about 2500 to 1700 years ago (500 B.C. to 300 A.D.). These results show that Greek and Roman lead and silver mining and smwlting activities polluted the middle troposphere of the Northern Hemisphere on a hemispheric scale two millenia ago, long before the Industrial Revolution. Cumulative lead fallout to the Greenland Ice Sheet during these eight centuries was as high as 15 percent of that caused by the massive use of lead alkyl additives in gasoline since the 1930s. Pronounce lead pollution is also observed during Medieval and Renaissance times.

Hong, S., Candelone, J.-P., Patterson, C.C. & Boutron, C.F. 1996. History of ancient copper smelting pollution during Roman and medieval times recorded in Greenland ice. Science, 272, 246-249.

Corresponding author: Sungmin Hong, Laboratoire de Glaciologie et Geophysique de l'Environnement, B.P. 96, 38402 St. Martin d'Heres Cedex, France.

Determination of copper concentrations in Greenland ice dated from seven millenia ago to the present showed values exceeding natural levels, beginning about 2500 years ago. This early large-scale pollution of the atmosphere of the Northern Hemisphere is attributed to emissions from the crude, highly-polluting smelting technologies used for copper production during Roman and medieval times, especially in Europe and China. This study opens the way to a quantitative assessment of the history of early metal production, which was instrumental in the development of human cultures during ancient eras.

Hong, S., Candelone, J.-P., Turetta, C. & Boutron, C.F. 1996. Changes in natural lead, copper, zinc and cadmium concentrations in central Greenland ice from 8250 to 149,100 years ago: their association with climatic changes and resultant variations of dominant source contributions. Earth and Planetary Science Letters, 143, 233-244.

Corresponding author: Sungmin Hong, Laboratoire de Glaciologie et Geophysique de l'Environnement, B.P. 96, 38402 St. Martin d'Heres Cedex, France.

We present here the first reliable time series of Pb, Cu, Zn and Cd in greenland ice for the last climatic cycle. They were obtained by analysing various sections of the 3028.8 m GRIP deep ice core drilled at Summit, central Greenland. Our results show that climatic changes have led to large variations in the concentrations of natural Pb, Cu, Zn and Cd in the high-latitude troposphere of the Northern Hemisphere. Between the interglacial and glacial periods, concentrations have varied by factors of 320 for Pb, 100 for Cu, 36 for Zn and 13 for Cd. Based on a good correlation between each heavy metal and Al, Pb and Cu are found to have mainly originated from soil and rock dust for both glacial and interglacial periods. On the other hand, continental biogenic emissions were the main source of Cd and to a lesser extent Zn in the Arctic troposphere during the warm Eemian and the Pre-Boreal to Holocene transition, whereas wind-blown dust was the predominant source for these two metals during the cold glacial climatic stages. This characteristic change of relative Cd and Zn contributions from different sources in contrast to that for Pb and Cu is well documented in the ice from the last deglaciation period (15,000 to 8250 yrs ago). After the Younger dryas event ended, a remarkable increase of Cd/Al and Zn/Al ratios occurred from 13,000 to 9300 yrs ago, which is consistent with the progressive expansion of vegetation following the retreat of the North American and North Eurasian ice sheets. The subsequent decrease of these ratios to Holocene values can be explained by the stabilization of atmospheric circulation in the northern high-latitude regions, which became similar to that for the Holocene due to further reduction of the Laurentide ice sheet. Finally, the observed variations of the metal/Al ratios suggest changes in the soil and rock dust source regions in parallel with climatic changes which have altered the mean composition of the crustal particles transported to the Arctic.

Laj, P., Ghermandi, G., Cecchi, R., Maggi, V., Riontino, C., Hong, S.M., Candelone, J.P. & Boutron, C. 1997. Distribution of Ca, Fe, K, and S between soluble and insoluble material in the Greenland Ice Core Project ice core. Journal of Geophysical Research, 102, 26615-26623.

Corresponding author: Paolo Laj, Institute for Physics and Chemistry of the Atmosphere, CNR, Via Gobetti 101, 40129 Bologna, Italy.

We have developed an original method coupling particle induced X ray emission and scanning electron microscope/X ray dispersive analysis in order to characterize the partitioning of Fe, Ca, K, and S between the soluble and the insoluble phases in wind-blown deposits in the Greenland ice. We applied this technique to several sections of the Greenland Ice Core Project ice core. We found that the dominant fraction (from 25 to 100%) of Ca and S deposited in Greenland is soluble, while the proportion of soluble material is lower for K and Fe (between 10 and 80%). For all elements the distribution between soluble and insoluble material varies according to the ice-core depth. The distribution appears to be linked to either meteorological factors, such as temperature or pH of the precipitation (in the case of Ca or S), or the alterability of the mineral assemblages found in the ice (in the case of Fe and K). The fraction of soluble material is therefore linked to the characteristics of source origin (S is predominantly emitted in very soluble forms) and to the dissolution of certain minerals (such as calcium carbonate or Fe-oxides) during transport in the atmosphere. The dynamics of alteration processes is, however, still uncertain, especially for K-containing minerals.

Legrand, M., de Angelis, M., Staffelbach, T., Neftel, A. & Stauffer, B. 1992. Large perturbations of ammonium and organic acids content in the Summit-Greenland ice core. Fingerprint from forest fires? Geophysical Research Letters, 19, 473-475.

Corresponding author: Michel Legrand, Laboratoire de Glaciologie et Geophysique de l'Environnement, B.P. 96, 38402 St. Martin d'Heres Cedex, France.

Biomass burning is influencing the atmospheric chemistry by emitting large amounts of reactive species such as hydrocarbons, organic acids and nitrogen compounds [Andreae et al., 1988]. Polar ice cores provide a unique record of precipitation whose chemistry reflects the atmospheric composition at the time of deposition. The analysis of such ice samples therefore allows an estimate to be made of the concentration of atmospheric impurities in the past. During the first season of the deep drill operation (GRIP) at Summit, Central Greenland (72 34' N, 37 38'W) continuous ammonium (NH4+) measurements were performed between 100 and 600 m depth covering the time period from 330 to 2500 years B.P. The NH4+ concentrations show seasonal variations between 1-20 ng.g-1 with some sporadic high values up to 600 ng.g-1 in narrow layers. Tne chemical fingerprint points to biomass burning causing the high ammonium peaks.

Legrand, M., de Angelis, M. & Maupetit, F. 1993. Field investigation of major and minor ions along Summit (central Greenland) ice cores by ion chromatography. Journal of Chromatography, 640, 251-258.

Corresponding author: Michel Legrand, Laboratoire de Glaciologie et Geophysique de l'Environnement, B.P. 96, 38402 St. Martin d'Heres Cedex, France.

As a part of the European EUROCORE and GRIP (Greenland Ice Core Project) operations aimed at recovering deep ice cores at Summit (Central Greenland), we have for the first time successfully performed ion chromatography measurements in the field and investigated in detail the soluble impurities, including Na+, NH4+, K+, Mg2+, Ca2+, F-, CH3COO-, CH2OHCOO-, HCOO-,CH3SO3-, Cl-, NO2-, SO42- and C2O42-, trapped in ice deposited over some 200 000 years in Greenland.

Legrand, M. & de Angelis, M. 1995. Origins and variations of light carboxylic acids in polar precipitation. Journal of Geophysical Research, 100, 1445-1462.

Corresponding author: Michel Legrand, Laboratoire de Glaciologie et Geophysique de l'Environnement, B.P. 96, 38402 St. Martin d'Heres Cedex, France.

Central Greenland and East Antarctic ice cores have been studied to investigate the carboxylic acid (acetate, CH3COO-; formate, HCOO-; glycolate, C2H303-; and oxalate, C2O4--) content of high-latitude precipitation. The two records cover the end of the last glacial age, the last great climatic change having occurred between 10,000 and 15,000 years B.P., and the Holocene period which started some 10,000 years ago. Carboxylic acids were measured using ion chromatography. These measurements are more difficult and require more stringent precautions to prevent sample contamination than inorganic trace species measurements. Carboxylic acids account for up to 25% of the free acidity in Greenland and are one order of magnitude more abundant in Greenland than in Antarctic precipitation. In Greenland precipitation deposited under present climatic conditions, formic and acetic acids are both present at the 10 ng g-1 level and are the most abundant carboxylic acids, while glycolic and oxalic acids with concentrations close to 1 ng g-1 represent minor carboxylic acid species. The level of formic, and to a lesser extent acetic, acid is also found to be strongly pH dependent. There is less formic acid at depths corresponding to periods when the acidity of the atmosphere was enhanced by a volcanic activity. Over the last 12,700 years, the carboxylic acid level of Greenland precipitation has often been sporadically enhanced by several orders of magnitude. Such large perturbations, which are accompanied by large increases of NH4+ concentrations, are probably caused by biomass-burning events which occurred at high northern latitudes. A particular chemical feature appears in snow layers corresponding to biomass-buming events which occurred during the Younger Dryas (11,550 to 12,700 years B.P.). During this cold stage, the precipitation was alkaline and the events were accompanied by an input of nitrite suggesting that peroxyacetyl nitrate (PAN) was present in the atmosphere and was hydrolysed in alkaline cloud water. Formate and acetate profiles indicate that background levels of these carboxylic acids were 5 and 2 times lower, respectively, during the last glacial maximum (15,000 to 34,000 years B.P.) than during the Holocene stage in Greenland precipitation. The increases of the acetate and formate snow contents in response to the glacial-interglacial climatic transition exhibit a time lag of some 5000 years. In particular, the formic acid increase follows perfectly the timing of the retreat of the Laurentide ice sheet from 18,000 years B.P. to the mid-Holocene stage (6000 years B.P.). Our data suggest therefore that carboxylic acids in Greenland precipitation are mainly linked to emissions from the high-latitude continental biosphere. In contrast, the in-cloud oxidation of formaldehyde produced from methane oxidation under acidic conditions likely represents the main source of formic acid in East Antarctica. Finally, the study of recent Greenland snow deposits indicates that the expected trend of carboxylic acid concentrations due to man-made activities is counteracted by a simultaneous increase of the acidity related to growing fossil fuel combustion, which leads to a less efficient uptake of carboxylic acids into precipitation.

Legrand, M. & de Angelis, M. 1996. Light carboxylic acids in Greenland ice: A record of past forest fires and vegetation emissions from the boreal zone. Journal of Geophysical Research, 101, 4129-4145.

Corresponding author: Michel Legrand, Laboratoire de Glaciologie et Geophysique de l'Environnement, B.P. 96, 38402 St. Martin d'Heres Cedex, France.

Measurements of light carboxylic acids (formate, HCOO-; acetate, CH3COO-; glycolate, C2H303-; and oxalate, C204--) were performed along Summit (central Greenland) ice cores covering the last two centuries and a complete glacial-interglacial cycle. High-latitude biomass burning contributes between 20% and 30% to the formate, oxalate, glycolate, and ammonium deposited on central Greenland over the last 200 years. This biomass burning contribution is very weak for nitrate and acetate. A decreasing trend in formate, parallel to the increasing strong acidity (H2S04 and HNO3) is observed over the last decades. This lack of record of the growing anthropogenic emissions of formic acid and of their precursors (nonmethane hydrocarbons and CH4) likely results from a less efficient scavenging of this weak acid from the gas phase into precipitation due to the recent acidification of the atmosphere. In contrast, the acetate profile shows a well-marked increase over the last three decades. This difference in the formate and acetate trends remains difficult to explain in the light of our present knowledge of anthropogenic emissions. The role of peroxyacetyl nitrate (PAN) acting as a reservoir for acetic acid in polar regions is a possibility which needs to be investigated. Aside from high-latitude biomass burning events which frequently occurred in the past except during the ice age maximum (15,000 to 40,000 years B.P.), the background levels of HCOO- and CH3C00- are lower during the ice age with respect to values observed during warm stages. Changes in vegetation emissions from North America are suggested to be responsible for the variations of formate background level observed in Greenland ice over the last 100,000 years. Greenland ice therefore contains information on the history of the Laurentide ice sheet, suggesting a well-established Laurentide ice sheet between 15,000 and 78,000 years B.P. and large fluctuations of its extent before 70,000 years B.P. Although the interpretation of the acetate profile remains more speculative, our data suggest that marine emissions of hydrocarbons may be an additional significant source of acetate.

Legrand, M., Hammer, C., DeAngelis, M., Savarino, J., Delmas, R., Clausen, H. & Johnsen, S.J. 1997. Sulfur-containing species (methanesulfonate and SO4) over the last climatic cycle in the Greenland Ice Core Project (central Greenland) ice core. Journal of Geophysical Research, 102, 26663-26679.

Corresponding author: Michel Legrand, Laboratoire de Glaciologie et Geophysique de l'Environnement, B.P. 96, 38402 St. Martin d'Heres Cedex, France.

A high-resolution profile covering the last two centuries and a discontinuous study spanning the complete last glacial-interglacial cycle of methanesulfonate (MSA) (CH,SO,) and sulfate were obtained along Summit (central Greenland) ice cores. MSA concentrations were close to 4 +/- 1.4-ng g(-1) from 1770 to 1870 A.D. and 3 ng g(-1) in 1900, and exhibited a well-marked decreasing trend from 1945 to the present. These changes of Summit snow MSA concentrations between 1770 and 1945 are discussed in terms of possible modulation of dimethylsulfide (DMS) marine emissions influencing the Greenland Ice Sheet by past climatic fluctuations in these regions. The decrease of MSA levels in Summit snow layers deposited since 1945 suggests either a decline in marine biota at high northern latitudes or a changing yield of MSA from DMS oxidation driven by modification of the oxidative capacity of the atmosphere in response to increasing anthropogenic NO, and hydrocarbon emissions. While interglacial ice concentrations of MSA and sulfate are close to 2.9 +/- 1.9 ng g(-1) and 27 +/- 10 ng g(-1), respectively, reduced MSA (1.2 +/- 0.7 ng g(-1)) and enhanced sulfate (55 +/- 19 ng g(-1)) levels characterized the early Holocene stage (9000 to 11,000 years B.P.). MSA concentrations in glacial ice remain similar to the ones observed during interglacial stages. In contrast, sulfate levels are strongly enhanced (243 +/- 84 ng g(-1)) during the last glacial maximum (14,400 to 15,700 B.P.) compared with the interglacial ones. These variations of sulfur-containing species in response to past climatic conditions are similar to those found in other Greenland cores. In contrast, they are different from those revealed in the Antarctic Vostok ice core, where colder climates were associated with an increase by a factor of 5 and 2 in MSA and sulfate concentrations, respectively. These glacial-interglacial changes are discussed in terms of present and past contributions of marine DMS emissions versus other sulfate sources such as volcanic emissions and continental dust to the Greenland precipitation.

Maggi, V. 1997. Mineralogy of atmospheric microparticles deposited along the Greenland Ice Core Project ice core. Journal of Geophysical Research, 102, 26725-26734.

Corresponding author: Valter Maggi, Dipartimento di Scienze dell'Ambiente e del Territorio, Universita di Milano, Via Emanueli 15, 20126 Milan, Italy.

The mineralogical composition of atmospheric dust particles changes along the Greenland Ice Core Project (GRIP) ice core in phase with other paleoatmospheric records, showing that climatic changes affect the location, the relative extent, and the surface characteristics of the dust source areas. Fifty GRIP ice samples from the Eemian to the last glacial maximum were analyzed using a scanning electron microscope coupled with X ray energy dispersive system microprobe. More than 20 mineral types or groups were identified and their relative abundance was evaluated. A different mineralogical composition was systematically observed in cold and warm time periods. Quartz, illite, chlorite, micas, and feldspars prevail in the mineral assemblage associated with cold stages or phases (marine isotope stage (MIS) 4, MIS 2, cold part of MIS 3 fast variations), while kaolinite and Fe (hydr)oxides dominate in warm episodes (MIS 5e(5), warm parts of fast variations). The first dust mineral assemblage is related mainly to the mechanical weathering prevailing in arid and cold mid-high-latitude areas, while the second dust mineral assemblage is related mainly to deep chemical weathering in warm and humid low-latitude areas. K/C and O/Q ratios may be assumed as indicative of the relative importance of low-latitude versus arid and mid-high-latitude source areas. It is worthwhile to mention that the first warmer part of Eemian (5e(5)) differs in dust mineralogy from the second part (5e(4)-5e(1)) and that also the fast variations are accompanied by clear mineralogical changes of the dust microparticles. The changes of the atmospheric dust mineral background are possibly related to changes of the atmosphere dynamics (meridian pressure gradient, polar front shift, storm track changes, etc.) and or to changes in the relative extent of the deflation source areas.

Mayewski, P.A., Meeker, L.D., Morrison, M.C., Twickler, M.S., Whitlow, S.I., Ferland, K.K., Meese, D.A., Legrand, M.R. & Steffensen, J.P. 1993. Greenland ice core "signal" characteristics: An expanded view of climate change. Journal of Geophysical Research, 98, 12839-12847.

Corresponding author: Paul Mayewski, Glacier Research Group, EOS/SERB, University of New Hampshire, Durham, New Hampshire 03824, USA.

The last millenium of earth history is of particular interest because it documents the environmental complexities of both natural variability and anthropogenic activity. We have analysed the major ions contained in the Greenland Ice Sheet Project 2 (GISP 2) ice core from the present to ~674 A.D. to yield an environmental reconstruction for this period that includes a description of nitrogen and sulfur cycles, volcanic emissions, sea salt and terrestrial influences. We have adapted and extended mathematical procedures for extracting sporadic (e.g., volcanic) events, secular trends, and periodicities found in the data sets. Finally, by not assuming that periodic components (signals) were "stationary" and by utilizing evolutionary spectral analysis, we were able to reveal periodic processes in the climate system which change in frequency, "turn on," and "turn off" with other climate transitions such as that between the little ice age and the medieval warm period.

Moore, J.C. 1993. High resolution dielectric profiling of ice cores. Journal of Glaciology, 39, 245-248.

Corresponding author: John Moore, (now at) Arctic Centre, University of Lapland, Box 122, SF-96101 Rovaniemi, Finland.

A new method for high-resolution (3 mm) dielectric profiling of ice cores is described. The method measures the capacitance and conductance of the ice at a single frequency (chosen to be 50 kHz in this case). The technique requires only a few minutes per metre of core, and no sophisticated data analysis. The system is designed to operate on ice cores that have been cut longitudinally, providing one flat and one curved surface. The 50 kHz conductance is dependent on the acid and neutral-salt concentrations in the ice. The new method was tested successfully on the GRIP core from Summit, Greenland, in 1991. It is useful for detecting seasonal variations in impurities in both acidic Holocene ice and in normally alkaline Wisconsin ice.

Moore, J.C., Wolff, E.W., Clausen, H.B., Hammer, C.U., Legrand, M.R. & Fuhrer, K. 1994. Electrical response of the Summit-Greenland ice core to ammonium, sulphuric acid, and hydrochloric acid. Geophysical Research Letters, 21, 565-568.

Corresponding author: John Moore, (now at) Arctic Centre, University of Lapland, Box 122, SF96101 Rovaniemi, Finland.
E-mail: jmoore@levi.urova.fi or
Eric Wolff, British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, United Kingdom.
E-mail: e.wolff@bas.ac.uk

Electrical and chemical analysis of the GRIP ice core from Summit in central Greenland confirms that the ECM current is controlled solely by acids in the ice, though there could be different responses for different acids. The dielectric conductivity is dependent on strong acid, on sea salt chloride, and also on ammonium concentrations in the ice. The response to NH4+ is similar to that of sea salt chloride, as they both conduct only at AC frequencies, but NH4+ is approximately twice as conductive per mole. The response to the strong acids shows results consistent with earlier work, with similar responses throughout the length of the core. It seems as if all the thousands of electrical peaks in the GRIP core may be explained by the response to just three chemical species: acidity, ammonium salts, and a third component which is probably chloride.

Neftel, A. & Fuhrer, K. 1993. A record of atmospheric oxidant from polar ice cores over the past 100,000 years: dream or real possibility? In Niki, H. & Becker, K.-H., eds. The tropospheric chemistry of ozone in the polar regions. Berlin Heidelberg: Springer Verlag.

Corresponding author: Albrecht Neftel, Eidgenossische Forschungsanstalt fur Agrikulturchemie und Umwelthygiene, CH-3097 Liebefeld-Bern, Switzerland.

No abstract, but summary follows. This paper discusses the use of polar ice cores as archive for atmospheric oxidants (ozone, OH radical and hydrogen peroxide are principle oxidants of interest; measurements are made of hydrogen peroxide and formaldehyde). The paper shows current knowledge about their concentration in ice cores. Difficulties with interpretation due to uncertainties over the air/snow transfer function require addressing urgently.

Sigg, A., Fuhrer, K., Anklin, M., Staffelbach, T. & Zurmuhle, D. 1994. A continuous analysis technique for trace species in ice cores. Environmental Science and Technology, 28, 204-210.

Corresponding author: Katrin Fuhrer, Physikalisches Institute, University of Bern, Sidlerstrasse 5, CH 3012 Bern, Switzerland.

A continuous melting technique, combined with continuous flow analysis, has been developed for in situ measurements of chemical trace species in ice cores. A cross-section of 1.8 x 1.8 cm2 of the core is needed for the simultaneous analysis of at least four species. The subcore is melted continuously from one side, and only the inner, uncontaminated part of the melted sample is used for the analysis. The main advantage of this method as compared to conventional sampling and analysis procedures is given by a very high spatial resolution, combined with a significant reduction of sample handling work. The method can be applied for any species for which a sensitive continuous flow analysis method exists. This technique has been applied successfully for the parallel measurement of H2O2, HCHO, NH4+, and Ca2+ during the Greenland Ice Core Project (GRIP) deep drilling project at Summit, central Greenland (72 34'N, 37 38'W, 3200 m above mean sea level).

Steffensen, J.P., Clausen, H.B., Hammer, C.U., Legrand, M. & DeAngelis, M. 1997. 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, 102, 26747-26754.

Corresponding author: Jorgen-Peder Steffensen, Department of Geophysics, The Niels Bohr Institute of Astronomy, Physics and Geophysics, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen N, Denmark.

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 delta(18)O 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 [Chappellaz 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, events 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 profiles. 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 explanation.

Steffensen, J.P. 1997. The size distribution of microparticles from selected segments of the Greenland Ice Core Project ice core representing different climatic periods. Journal of Geophysical Research, 102, 26755-26763.

Corresponding author: Jorgen-Peder Steffensen, Department of Geophysics, The Niels Bohr Institute of Astronomy, Physics and Geophysics, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen N, Denmark.

The size distribution of insoluble microparticles (dust) in the particle size interval 0.4-6.0 mu m radius has been measured in more than 1400 samples from the Greenland Ice Core Project (GRIP) deep ice core from Summit, Greenland. The samples were taken from ice core segments representing 32 climatic periods including ice from the Eem interglacial and ice from below the Eemian ice. The mean dust volume distributions from the climatic periods are compared, and the relationship of total dust mass to the concentration of Ca2+ and to the stable isotopic composition (delta(18)O) is investigated. The dust volume distributions are found to be lognormal in the size interval 0.4-2.0 mu m with nearly identical shapes. Changes of the lognormal part of the volume distributions are found to be connected to the total dust mass in a systematic way. The total dust mass is correlated to the Ca2+ concentration, and data do not show any enrichment in Ca2+ from exposed continental shelves due to lower sea levels during the last glacial maximum. The total dust mass is strongly connected to delta(18)O. The volume distribution of the particles in the size interval 2.0-6.0 mu m is found to be almost the same in most periods. The exceptions are the ''cold'' periods in the last part of the last glacial period, where the volume of these particles is higher than in most periods, and the periods from the Eemian and just above the Eemian where the volume of these particles is lower. The volume distributions of both the Eemian ''warm'' periods and the ''cold'' Eemian events are different from the distributions in ice from both below and above the Eemian ice. Climate changes appear to have modified the processes of production, transport, modification, and deposition of the dust aerosol in the same way over the last 120,000 years or more.

Taylor, K.C., Hammer, C.U., Alley, R.B., Clausen, H.B., Dahl-Jensen, D., Gow, A.J., Gundestrup, N.S., Kipfstuhl, J., Moore, J.C. & Waddington, E.D. 1993. Electrical conductivity measurements from the GISP2 and GRIP Greenland ice cores. Nature, 366, 549-552.

Corresponding author: Kendrick Taylor, Box 60220, Desert Research Institute, University of Nevada, Reno, Nevada 89506, USA.

The direct-current conductivity of glacial ice depends on its acidity, and can also indicate changes in climate, as ice formed in cold, dusty periods has a high concentration of alkaline dust, which significantly reduces the conductivity compared to warmer, less dusty periods. Here we present electrical conductivity records for the Greenland Ice Sheet Project 2 (GISP2) and Greenland Ice-core Project (GRIP) ice cores, drilled 28 km apart to enable direct comparison of the results. The upper parts of both records are consistent with previous evidence from other Greenland cores for a stable Greenland climate during the Holocene, and a series of warm events punctuating the last glacial period. However, there is a significant discrepancy between the two records in the bottom 10% of the cores, calling into question recent reports of climate variability in the last intergiacia1 and the penultimate glaciation. At this stage, it is too early to say what exactly is causing the discrepancy, although ice flow may have introduced some discontinuities into the records. Further work will be necessary to establish how much climatic information it will eventually be possible to extract from the lower parts of the two cores.

Wolff, E.W. & Reid, A.P. 1994. Capture and scanning electron microscopy of individual snow crystals. Journal of Glaciology, 40, 195-197.

Corresponding author: Eric Wolff, British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, United Kingdom.
E-mail: e.wolff@bas.ac.uk

A snow crystal has been successfully collected on to a scanning electron microscope (SEM) stub in central Greenland. It was preserved at liquid nitrogen temperature for 5 months, prior to examination in the SFM. This is believed to be the first time a snow crystal has been observed directly in the SEM and offers some new experimental methods for understanding crystals and their chemistry.

Wolff, E.W., Moore, J.C., Clausen, H.B., Hammer, C.U., Kipfstuhl, J. & Fuhrer, K. 1995. Long-term changes in the acid and salt concentrations of the GRIP Greenland ice core from electrical stratigraphy. Journal of Geophysical Research, 100, 16249-16264.

Corresponding author: Eric Wolff, British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK.
E-mail: e.wolff@bas.ac.uk

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.

Wolff, E.W., Moore, J.C., Clausen, H.B. & Hammer, C.U. 1997. Climatic implications of background acidity and other chemistry derived from electrical studies of the Greenland Ice Core Project ice core. Journal of Geophysical Research, 102, 26325-26332.

Corresponding author: Eric Wolff, British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK.
E-mail: e.wolff@bas.ac.uk

High-resolution continuous profiles were obtained on the Greenland Ice Core Project (GRIP) ice core using two different electrical methods. After correction for temperature and density, the electrical conductivity method (ECM) technique responds only to acidity, while dielectric profiling (DEP) responds to acid, ammonium, and chloride. Detailed chemistry on a section of glacial-age ice allows us to confirm the calibration factor for chloride in DEP. Acidity dominates the DEP variability in the Holocene, Allerod/Bolling, and larger interstadials; ammonium dominates in the Younger Dryas, while chloride is the major contributor in cold periods including smaller interstadials. From the electrical signals plotted on a linear timescale we can deduce the background (nonvolcanic) acidity of the ice, varying from always acidic in the Holocene to always alkaline in the cold periods. In the interstadials, the ice is close to neutral, with most of it acidic in larger interstadials, most of it alkaline in smaller ones, and rapid alternations within interstadials. It is not clear whether neutralization of individual acidic particles occurred in the atmosphere or whether acid and alkaline particles coexisted until deposition in the snowpack. The changes in acidity observed at GRIP apply at least to all of Greenland and probably to much of North America. There would have been ecological effects and important changes in the uptake of some chemicals onto ice. If acidic sulfate particles were neutralized and removed from the atmosphere, which remains uncertain, then there are atmospheric chemistry and radiative effects that require further investigation.

Zielinski, G.A., Mayewski, P.A., Meeker, L.D., Gronvold, K., Germani, M.S., Whitlow, S., Twickler, M.S. & Taylor, K. 1997. Volcanic aerosol records and tephrochronology of the Summit, Greenland, ice cores. Journal of Geophysical Research, 102, 26625-26640.

Corresponding author: Greg Zielinski, Climate Change Research Center, Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, NH 03824, USA.

The recently collected Greenland Ice Sheet Project 2 (GISP2) and Greenland Ice Core Project ice cores from Summit, Greenland, provide lengthy and highly resolved records of the deposition of both the aerosol (H2SO4) and silicate (tephra) components of past volcanism. Both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism-climate system. The continuous time series of volcanic SO42- for the last 110,000 years show a strong relationship between periods of increased volcanism and periods of climatic change. The greatest number of volcanic SO42- signals, many of very high magnitude, occur during and after the final stages of deglaciation (6000-17,000 years ago), possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins (sea level change). The increase in the number of volcanic SO42- signals at 27,000-36,000 and 79,000-85,000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation, respectively. A comparison of the electrical conductivity of the GISP2 core with that of the volcanic SO42- record for the Holocene indicates that only about half of the larger volcanic signals are coincident in the two records. Other volcanic acids besides H2SO4 and other SO42- sources can complicate the comparisons, although the threshold level picked to make such comparisons is especially critical. Tephra has been found in both cores with a composition similar to that originating from the Vatnaoldur eruption that produced the Settlement Layer in Iceland (mid-A.D. 870s), from the Icelandic eruption that produced the Saksunarvatn ash (similar to 10,300 years ago), and from the Icelandic eruption(s) that produced the Z2 ash zone in North Atlantic marine cores (similar to 52,700 years ago). The presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras. The presence of both rhyolitic and basaltic shards in the Z2 ash in the GISP2 core and the composition of the basaltic grains lend support to multiple Icelandic sources (Torfajokull area and Katla) for the Z2 layer. Deposition of the Z2 layer occurs at the beginning of a stadial event, further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions.