Volcanic tephra are independent age horizons and can synchronize strata of various paleoclimate records including ice and sediment cores. The Holocene section of the Greenland Ice Core Project (GRIP) ice core is dated by multi-parameter annual layer counting, and contains peaks in acidity, SO42− and microparticle concentrations at a depth of 429.1 to 429.3 m, which have not previously been definitively ascribed to a volcanic eruption. Here, we identify tephra particles and determine that volcanic shards extracted from a depth of 429.3 m in the GRIP ice core are likely due to the 79 AD Vesuvius eruption. The chemical composition of the tephra particles is consistent with the K-phonolitic composition of the Vesuvius juvenile ejecta and differs from the chemical composition of other major eruptions (≥ VEI 4) between 50–100 AD.

New and well‐dated evidence of sulphate deposits in Greenland and Antarctic ice cores indicate a substantial and extensive atmospheric acidic dust veil at A.D. 533–534 ± 2 years. This was likely produced by a large explosive, near equatorial volcanic eruption, causing widespread dimming and contributing to the abrupt cooling across much of the Northern Hemisphere known from historical records and tree‐ring data to have occurred in A.D. 536. Tree‐ring data suggest that this was the most severe and protracted short‐term cold episode across the Northern Hemisphere in the last two millennia, even surpassing the severity of the cold period following the Tambora eruption in 1815.

The S(O)-proflle along the Little America V ice core ranges from — 20°/00 near the surface to — 35%o at the bottom, i.e. lower than at any surface value hitherto measured in West Antarctica. Le profil des isotopes stables à travers le Ross Ice Shelf à Little America V, Antarctique Résumé. Les teneurs isotopiques 3(0) mesurées dans la carotte de Little America V varient de — 20%0 vers la surface à — 35°/o0 à la base; elles sont alors plus basses que les valeurs mesurées jusqu'alors en surface dans l'Antarctique de l'Ouest. A core drilling operation was conducted at Little America V (78°10'S, 168°13'W) on the Ross Ice Shelf, Antarctica, during the austral summer 1958 (Ragle et al, 1960). This was the first successful continuous core drilling through a floating ice shelf and resulted in the recovery of a 254.5-m long, 10-cm diameter ice core from the surface to near the ice/sea water interface. Crary et al.'s (1962) mass balance considerations suggested that the Ross Ice Shelf is in near equilibrium at present. Other opinions have been presented since then (Hughes, 1973), and recent gross /3-activity measurements (Clausen and Dansgaard, 1977) on samples from far inland show only half the accumulation hitherto assumed. However, the only new accumulation figure FIGURE 1. 'Snowshed' area (enclosed by the thin, dashed curve) of the northeastern part of the Ross Ice Shelf as estimated by Crary et al. (1962). Heavy, full curve: shoreline/ barrier of the Ross Ice Shelf. Heavy, dashed curve: Marie Byrd Land grounding line/ Roosevelt Island. Thin curves: ice flow lines. Heavy dashed-dotted curve: flow line through Little America V, estimated and used by Crary et al. (1962) for computation of vertical flow pattern shown in Fig. 2.

SESSION 1: LATE QUATERNARYCLIMATE FROM ICE CORES,1: GREENLAND CLIMATE OF THE LAST 150 000 YEARS Dorthe Dahl-Jensen, Niels S. Gundestrup, Heinz Miller, OkitsuguWatanabe, SigfüsJ. Johnsen, JÖrgen P. Steffensen, Henrik B. Clausen, Anders Svensson and Lars B. Larsen: The NorthGRIP deep drilling programme Sune Olander Rasmussen, Katrine Krogh Andersen, Marie-Louise Siggaard-Andersen and Henrik B. Clausen: Extracting the annual signal from Greenland ice-core chemistry and isotopic records ThorsteinnThorsteinsson,YunWang, Josef Kipfstuhl, Heinz Miller and Hitoshi Shoji: The normal grain-growth regime in the NGRIP deep ice core compared with other Greenland locations JÖrgen Peder Steffensen and Dorthe Dahl-Jensen: An attempt to understand some of the chemical profiles of the Eemian and deeper ice in the GRIP core Niels Reeh, Hans Oerter and Henrik HÖjmarkThomsen: Comparison between Greenland ice-margin and ice-core oxygen18 records Roy M. Koerner and David A. Fisher: Ice-core evidence for widespread Arctic glacier retreat in the Last Interglacial and the early Holocene

The 345 m long ice core retrieved from the Hans Tausen Ice Cap in 1995 (82,5°N, 38°W) in Western Peary Land was sampled in situ for later paleoclimatic δ18Omeasurements in Copenhagen. The upper 125 m covers a little more than 1000 years and indicates strong persistent warming from the late 1920-ties, a maximum warming in the early 1960-ties and a variable climate with no particular trend since the 1960-ties. The δ record over the past 100 years shows similarities with the temperature records from the Greenland west coast stations, Iceland, and the Faroe Islands. The 20th century is the warmest in the entire record, while the periode 1700-1900 A.D. is the coldest during the past 2000 years. A maximum of warm climate seems to be reached around 900-1100 A.D. which then declines to the colder conditions around 1700 A.D. The climatic interpretation of the deepest 105 m of the δ record is more complicated due to the non-steady state of the ice cap: The implication for the paleoclimatic interpretation will be discussed. No glacial ice is present in the bottom ice.

The paper presents studies of various chemical and isotopical parameters from ice cores drilled in the northernmost located ice cap, Hans Tausen Iskappe, Pearyland, Greenland (HT). The 346 m main ice core (MC95) was drilled to bedrock in 1995 as well as a 35 m shallow core (SC95). A 60 m shallow core (SC75) and a 51 m shallow core (SC76) was drilled at two different positions in1975 and 1976, respectively. A 60 m shallow core (SC94) was drilled in 1994. Continuous stable isotope records exist for all of these cores, total β-activity only from SC75 and SC76. Continuous ECM inferred acidity records exist along the 1995 cores (MC95 and SC95) and finally detailed records of dust and water soluble ion concentrations exist on selected parts of MC95. To determine a time scale for the ice core is an important prerequisite for the interpretation of other records. The age scale is based on acid layers, caused by known volcanic eruptions, and by comparison of the chemical composition of these layers to that found in ice cores from other arctic locations. The total β-activity data from SC75 and SC76 provide fixed points to the time scale because a pronounced increase in total β-activity is related to the thermo-nuclear tests in the atmosphere in the early 1960'ies. Many of the investigated parameters exhibit seasonal variations e.g. δ18O, acidity, Cl– and dust, therefore the study of the accumulation history of the ice cap improves our knowledge of the question if the mass balance of the Hans Tausen Iskappe is in equilibrium or not. In the upper half part of the ice core the MC95 ECM record reveals several events of high acidity which can be connected to volcanic events known from other Greenland ice core records. Among the identified volcanic events are AD 1912 (Katmai, Alaska), AD 1815 (Tambora, Indonesia), AD 1783 (Laki, Iceland), AD 934 (Eldgjà, Iceland) and e.g. the signals of AD 1259 and 49 BC. The two latter signals originate from major volcanic eruptions of unknown eruption sites with a probable location close to the Equator in the case of the AD 1259 event. Some of the volcanic events are selected for an analysis of dust and water soluble chemical components, including F–, CH3SO2–, Cl–, NO3–, SO42–, Na+,NH4+, K+, Mg2+ and Ca2+. Coulter counter technique was used for the dust measurements and the chemical analysis were carried out by ion chromatography.

The analysis of air bubbles trapped in polar ice has permitted the reconstruction of past atmospheric concentrations of CO 2 over various timescales, and revealed that large climate changes over tens of thousands of years are generally accompanied by changes in atmospheric CO 2 concentrations 1 . But the extent to which such covariations occur for fast, millennial-scale climate shifts, such as the Dansgaard–Oeschger events recorded in Greenland ice cores during the last glacial period 2 , is unresolved; CO 2 data from Greenland 3 and Antarctic 4 ice cores have been conflicting in this regard. More recent work suggests that Antarctic ice should provide a more reliable CO 2 record, as the higher dust 5 content of Greenland ice can give rise to artefacts 1 , 6 , 7 . To compare the rapid climate changes recorded in the Greenland ice with the global trends in atmospheric CO 2 concentrations as recorded in the Antarctic ice, an accurate common timescale is needed. Here we provide such a timescale for the last glacial period using the records of global atmospheric methane concentrations from both Greenland and Antarctic ice. We find that the atmospheric concentration of CO 2 generally varied little with Dansgaard–Oeschger events (<10 parts per million by volume, p.p.m.v.) but varied significantly with Heinrich iceberg-discharge events (∼20 p.p.m.v.), especially those starting with a long-lasting Dansgaard–Oeschger event.

A central issue in climate dynamics is to understand how the Northern and Southern hemispheres are coupled during climate events. The strongest of the fast temperature changes observed in Greenland (so-called Dansgaard–Oeschger events) during the last glaciation have an analogue in the temperature record from Antarctica. A comparison of the global atmospheric concentration of methane as recorded in ice cores from Antarctica and Greenland permits a determination of the phase relationship (in leads or lags) of these temperature variations. Greenland warming events around 36 and 45 kyr before present lag their Antarctic counterpart by more than 1 kyr. On average, Antarctic climate change leads that of Greenland by 1–2.5 kyr over the period 47–23 kyr before present.

The 2191 m long ice core recovered at Byrd Station Antarctica in 1968 (BS68) was measured continuously by an electrical conductivity method (ECM). The ECM curve inferes the acidity of seasonal ice layers and major peaks, which identify clearly intermediate and prominent past volcanic activity over the last 50,000 years. We here also present recent data for a suite of the most striking volcanic events that occurred around 17.5 ka ± 0.5 BP. These events emitted enormous amounts of HCl and HF into the atmosphere.

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 Crête, 150 km south of the Summit region.

In a companion paper, Zolensky discusses interplanetary dust particles (IDP's) collected in the stratosphere. Here, we describe the recovery of much larger unmelted to partially melted IDP's from the Greenland and Antarctica ice sheet, and discuss problems arising in their collection and curation, as well as future prospects for tackling these problems.

The aim of this paper is to evaluate and exemplify the potential of continuous and high-resolution ice-core analysis in atmospheric-climatic research. At present only a few ice-core components of current interest can be measured continuously with high resolution along the cores. In this paper, the techniques of in-situ or “in the laboratory” continuous high-resolution measurement of solid-liquid electrical conductivity, pH, dust and anions will be presented and discussed. In particular, results from individual precipitation samples, seasonal changes, rare events, and the comparison of results from various Antarctic and Greenland ice cores will be discussed.

A strong volcanic-acid signal is clearly registered, using an acidity-measuring technique, in the A.D. 1259 ice layer in four different Greenland ice cores (Camp Century, Milcent, Crête and Dye 3). This signal is similar in amplitude to the Laki (Iceland) A.D. 1783 volcanic event as recorded in the central and south Greenland ice cores. Measurement of ice layers from corresponding age levels in Antarctic ice cores (Byrd Station, South Pole and J–9 on the Ross Ice Shelf) provides similar strong acid signals. There is no historical record of a significant volcanic eruption for the period around A.D. 1260 in the Northern Hemisphere. Subsequent chemical analyses of all A.D. 1259 ice layers show similar compositions. We suggest that the A.D. 1259 signals registered in both Greenland and Antarctica were caused by the same volcanic disturbance and that its epicenter was located at the Earth’s equatorial zone, which enabled global distribution of the acid gases. These results indicate that inter-hemispheric dating of ice sheets is possible by the chemical identification of major eruptive volcanic events in the equatorial zone.

Major volcanic eruptions deposit large amounts of strong acids in polar ice. Two such volcanic eruptions are Laki, A.D. 1783, at high latitude (64 °N), and Tambora, A.D. 1815, close to the Equator (8°S). The acid ice layers from these eruptions are easily reached by shallow drilling, and the acidity of the ice cores obtained has been determined by a solid electrical conductivity method (ECM), and in some cases by liquid pH measurements. The strong acid is identified by chemical anion analysis. Sulfate is the dominant anion in both of these volcanic events.Atmospheric thermonuclear-bomb tests ejected radioactive debris into the atmosphere. Two major groups of such tests are those carried out by the Americans in 1952-54 at low latitude (11°N) and by the Russians in 1961-62 at high latitude (75°N). Radioactive debris from these events was deposited in polar snow, and can be detected by specific total β activity measurements. The radioactive layers serve as dating horizons in the firn. The total β activities were measured at least 10 years after ejection, thus the measured activities were mainly due to 90Sr and 137Cs.The amount of 90Sr and 137Cs ejected into the atmosphere is known. We assumed a similar global distribution pattern of bomb-produced total β activity and strong acids from violent volcanic activity, and were able to calculate that both major volcanic events produced some 300 million tons of sulphuric acid. This is in agreement with other estimates of the Tambora eruption, which are based on studies of ice cores from Antarctica.

Greenland ice cores contain a broad spectrum of informations on past environmental conditions in the North Atlantic region. However, the ice flow pattern, which is particularly complicated in South Greenland, dictates correction of ice core data for thinning of annual layers since the time of formation, and/or for deviating conditions upstream from the drill site. Measurements on the changing geometry of the deep drill hole at Dye 3; on the surface and bedrock topographies; and on the surface velocities upstream, have been used as inputs to an ice flow model that has led to a deeper understanding of the ice dynamics that is needed for a proper correction proceedure. The corrected data series show that the annual precipitation in South Greenland has varied considerably less through the last several millenia, than suggested by the raw data. The interpretation of stable isotope data series is discussed, and examples of Pleistocene environmental data series are presented.

Polar ice cores offer datable past snow deposits in the form of annual ice layers, which reflect the past atmospheric composition. Trace substances in the cores are related to the past mid-tropospheric impurity load, this being due to the vast extent of the polar ice sheets (or ice caps), their surface elevations and remoteness from most aerosol sources. Volcanic eruptions add to the rather low background impurity load via their eruptive products. This paper concentrates on the widespread influence on atmospheric impurity loads caused by the acid gas products from volcanic eruptions. In particular the following subjects are discussed: acid volcanic signals in ice cores, latitude of eruptions as derived by ice-core analysis, inter-hemispheric dating of the two polar ice sheets by equatorial eruptions, volcanic deposits in ice cores during the last glacial period and climatic implications.