Analysis Of Ice Cores Research Articles

Paleoreconstruction of volcanic history inferred from glacio-chemical ice core analyses

Paleoreconstruction of volcanic history inferred from glacio-chemical ice core analyses

The Carrington event: Possible doses to crews in space from a comparable event

Recent ice core analyses suggest that the Carrington event of 1859 may have been the largest solar energetic particle event in the past several hundred years. Previous analyses of potential doses to humans and electronics from such an event suggested that a Carrington-like event, with a hard spectrum similar to that of the event of September 1989 could be catastrophic. Subsequent analyses of the 10Be concentration in the ice core data suggest that the spectral hardness of the Carrington event was softer and similar to the August 1972 event. In this work we review the earlier estimates of doses from a Carrington event, and present updated dose estimates for deep space crews and electronics using the Carrington event proton fluence ⩾30 MeV in combination with an event spectrum similar to that of the August 1972 event. Potential ramifications of these doses for humans and electronics on deep space missions are discussed.

Zonation of the Laptev Sea landfast ice cover and its importance in a frozen estuary

The interaction between river water and landfast sea ice was investigated through synthetic aperture radar (SAR) remote sensing, ice-growth modeling, and ground-based ice-core and hydrographic studies in the Laptev Sea, Siberian Arctic, in 1996/1997 and 1998/1999. Ice-core data in conjunction with ice-growth and SAR backscatter modeling demonstrated that the contrasts in dielectric and microstructural properties between freshwater/brackish (salinity < 1‰) and sea ice allow a mapping of the distribution of freshwater and brackish ice as influenced by Lena River discharge. This brackish zone (surface water salinities < 5) extended over 2000–3000 km 2 inshore of the 10-m isobath and exhibited distinct SAR backscatter coefficients and image texture. In the nearshore zone, bottomfast ice growth could be identified and tracked over the growth season. Occupying up to 250 km 2 along the Lena Delta, bottomfast ice was not as widespread as previously hypothesized, possibly due to ice being thinner by 10–20% relative to the long-term mean. In SAR and ERS-2 scatterometer data, Laptev Sea landfast ice exhibits the lowest backscatter signatures of any ice type in the Arctic Ocean, due to the lack of major deformation features. Stable-isotope data show that the landfast ice is composed of about 62% of river water, locking up 24% of the total annual Lena and Yana discharge. From ice-growth/isotopic-fractionation modeling and ice-core analysis, time series of surface water salinity have been derived, indicating freshening of under-ice waters during winter and north-/northeastward spreading of the river plume with under-ice spreading rates of 1.0–2.7 cm s − 1. A river freshwater budget for the inner Laptev shelf indicates flushing times of a year or more with cross-shelf export of 627 km 3 during the winter of 1998/1999. Based on these findings, the southeastern Laptev Sea can be considered an open, seasonally frozen estuary. This system contrasts with North American shelf environments, which show a different response to climate variability and change.

A 220 kyr record of Pb isotopes at Dome C Antarctica from analyses of the EPICA ice core

Pb isotopic compositions and Pb and Ba concentrations are reported in EPICA Dome C ice core samples dating to 220 kyr BP, indicating that Pb isotopic compositions in Antarctic ice vary with changing climate. 206Pb/207Pb ratios decrease during glacial periods, with the lowest values occurring during colder climatic periods (stages 2, 4 and 6) and the Holocene. Low Pb concentrations (&lt;1 pg/g) were found during the Holocene and the last interglacial (climate stage 5.5) while higher Pb concentrations (&gt;10 pg/g) were found during cold climatic periods. Ba, a proxy for mineral dust, was used to determine that dust usually accounts for ∼70% of Pb in Dome C ice, while the remaining ∼30% was attributed to volcanic emissions. Pb isotopic compositions at Dome C differ from those reported in pre‐industrial ice from other Antarctic locations, due to greater proportions of dust Pb at Dome C.

Effects of molecular diffusion on trapped gas composition in polar ice cores

Enrichment of nitrogen gas has been found from gas analyses of ice cores retrieved from deep parts of Antarctica. Neither climate change nor gas loss through ice cracks explain the enrichment. In order to investigate the mechanism of the gas composition change, we develop a model of gas loss caused by molecular diffusion from clathrate hydrates toward the ice-core surface through ice crystal. We apply the model to interpret the data on the gas composition change in the Dome Fuji ice core during the storage for 3 years at 248 K. The mass transfer coefficients determined using the model are 1.4×10 −9 and 4.3×10 −9 m·s −1 at 248 K for N 2 and O 2, respectively. The difference in the coefficient between N 2 and O 2 causes the change in the O 2/N 2 ratio of the trapped gas in the ice core during the storage. During the storage period of 1000 days at 248 K, the O 2/N 2 ratio changes from −9.9‰ to −20.5‰. The effect of the gas loss decreases as the storage temperature decreases. The results have important implications for the accurate reconstructions of the paleo-atmosphere from polar ice cores.

Relationship between calcium and atmospheric dust recorded in Guliya ice core

By the analyses of Guliya ice core on the Tibetan Plateau, it was found that the calcium (Ca2+) originated from the terrestrial source is the main cation of soluble aerosol and a good proxy of the atmospheric component and environment in the mountain ice core located in the mid-low latitude arid regions. Evident variation of Ca2+ concentration has been found in the Guliya ice core since the Last Interglaciation with two relatively strong increase periods and two weak increase periods. These variations are generally related to climatic changes: high Ca2+ concentration periods coincide with cold periods and low Ca2+ concentration periods coincide with warm periods. However, Ca2+ concentration does not always decrease (increase) with climate warming (cooling). The magnitude and phase of Ca2+ concentration does not always match temperature either. The changes of atmospheric circulation, land surface condition and atmospheric humidity might be important factors which influence Ca2+ concentration besides temperature.

On the role of grain growth, recrystallization and polygonization in a continuum theory for anisotropic ice sheets

AbstractWe outline how to incorporate microscale effects of polycrystalline ice into a continuum description. Actually, analyses of ice cores in Antarctica show that different microstructures generally produce different responses, i.e. a non-uniform distribution of c axes gives rise to anisotropic behaviour. It has been recognized that, to describe certain microstructural processes, like recrystallization or polygonization, we need a parameter able to switch them on (e.g. dislocation density or its associated lattice distortion energy). With this in mind, balance equations for a continuum theory of an anisotropic ice sheet undergoing recrystallization have been recently proposed. In this work, we examine relations for some constitutive quantities, in order to take into account the effects of grain-boundary migration, nucleation and polygonization. We check our assumptions by explicit comparison with the first 1200 m of the Byrd (Antarctica) ice core. Current literature usually gives a relation between normal grain growth and grain boundary migration rate. Here, an equation for normal grain growth which also incorporates the influence of polygonization is suggested. It is based on experimental data from the same core in Antarctica. Polygonization is a microscopic process, but here we present a continuum description of the bending stresses which promote the fragmentation of crystallites in terms of the theory of mixtures with continuous diversity.

Sensitivity of chemical species to climatic changes in the last 45 kyr as revealed by high-resolution Dome C (East Antarctica) ice-core analysis

AbstractTo assess the cause/effect relationship between climatic and environmental changes, we report high-resolution chemical profiles of the Dome C ice core (788m, 45 kyr), drilled in the framework of the European Project for Ice Coring in Antarctica (EPICA). Snow-concentration and depositional-flux changes during the last deglaciation were compared with climatic changes, derived by δD profile. Concentration and temperature profiles showed an anticorrelation, driven by changes in source intensity and transport efficiency of the atmospheric aerosol and by snow accumulation-rate variations. The flux calculation allowed correction for accumulation rate. While sulphate and ammonium fluxes are quite constant, Na+, Mg2+ and Ca2+ underwent the greatest changes, showing fluxes respectively about two, three and six times lower in the Holocene than in the Last Glacial Maximum. Chloride, nitrate and methanesulphonic acid (MSA) also exhibited large changes, but their persistence depends on depositional and post-depositional effects. The comparison between concentrations and δD profiles revealed leads and lags between chemical and temperature trends: Ca2+ and nitrate preceded by about 300 years the δD increase at the deglaciation onset, while MSA showed a 400 year delay. Generally, all components reached low Holocene values in the first deglaciation step (18.0–14.0 kyr BP), but Na+, Mg2+ and nitrate show changes during the Antarctic Cold Reversal (14.0– 12.5 kyr BP).

Variability in accumulation rates from GPR profiling on the West Antarctic plateau

AbstractIsochronal layers in firn detected with ground-penetrating radar (GPR) and dated using results from ice-core analyses are used to calculate accumulation rates along a 100 km across-flow profile in West Antarctica. Accumulation rates are shown to be highly variable over short distances. Elevation measurements from global positioning system surveys show that accumulation rates derived from shallow horizons correlate well with surface undulations, which implies that wind redistribution of snow is the leading cause of this variability. Temporal changes in accumulation rate over 25–185 year intervals are smoothed to along-track length scales comparable to surface undulations in order to identify trends in accumulation that are likely related to changes in climate. Results show that accumulation rates along this profile have decreased in recent decades, which is consistent with core-derived time series of annual accumulation rates measured at the two ends of the radar profile. These results suggest that temporal variability observed in accumulation-rate records from ice cores and GPR profiles can be obscured by spatial influences, although it is possible to resolve temporal signals if the effects of local topography and ice flow are quantified and removed.

Stratigraphic analysis of Dome Fuji Antarctic ice core using an optical scanner

AbstractLong-term changes of snow-accumulation rate in Antarctica are a major uncertainty in our understanding of past climate. Because the visible strata in polar ice are due to variations in the sizes and concentrations of air inclusions and microparticles, the scattered light intensity from an ice core yields valuable information on the stratification, which is likely to provide estimates of the annual accumulation rates. Identification of each layer is therefore necessary, and we developed an optical scanner apparatus to record detailed visible strata of ice cores. The apparatus records the two-dimensional distribution of light-scattering intensity along ice-core samples and produces an image of the whole ice-core sample by an image analysis process. These images showed that ice from Dome Fuji ice core contained a large number of layers. Volcanic layers were also well identified. We processed the scattering intensity on the enhanced intensity images to produce an intensity profile. This profile showed that the period of the intensity variations is consistent with a core-dating model applied to the Dome Fuji ice core. We also found that the intensity peaks are closely correlated to peaks in Ca2+ ion concentrations. Thus, our scanning method is a promising approach to measuring annual-layer thickness and, as a result, may be used to infer past accumulation rates in Antarctica.

International ice core community meets to discuss best practices for ice core curation

Several countries now have national ice core laboratories, or substantial ice core facilities, where these proxy archives of the Earth's past climate and atmosphere are safeguarded, processed, and analyzed. Australia, China, Denmark, Japan, Argentina, and the United States have formal, dedicated ice core repositories with laboratories. India's is under construction, in Goa. France, Germany, Russia, and the U.K. have long had substantial ice core holdings and facilities for analysis of ice cores. Brazil, Chile, Italy, and Switzerland have expanding field acquisition and analytical programs that require favorable storage conditions for ice cores.Representatives of 12 countries gathered in Milan, Italy, in late August for a first meeting, InterICE, of “international ice core establishments,” to compare and discuss ideas about best practices for acquisition, storage, curation, and distribution of the ice cores that have been drilled from the polar and temperate glaciers of the world, representing up to a half‐million years of the Earth's most recent past.

Climat du passé (400 000 ans) : des temps géologiques à la dérive actuelle

Resume Depuis une quinzaine d'annees, l'etude du climat du passe a fourni nombre de resultats pertinents vis-a-vis de son evolution future. Ils concernent, en particulier, la mise en evidence d'une relation entre climat et effet de serre et la decouverte de variations climatiques rapides. Ils s'appuient sur des enregistrements qui couvrent les derniers cycles climatiques, tels que ceux obtenus a partir de l'etude du forage glaciaire de Vostok, qui permet de decrire l'evolution du climat de l'Antarctique et celle de la composition de l'atmosphere sur plus de 400 000 ans. Cette periode est egalement de mieux en mieux documentee a partir d'enregistrements oceaniques et continentaux. Nous illustrons, a partir de quelques exemples s'appuyant sur des travaux recents dans lesquels des equipes francaises sont fortement impliquees, quelques-uns des resultats marquants obtenus a partir de l'etude de carottages en regions polaires, de sediments marins et d'archives continentales. Pour citer cet article : J. Jouzel, C. R. Geoscience 335 (2003).

Science goals for a Mars polar-cap subsurface mission: optical approaches for investigations of inclusions in ice

AbstractThe Mars polar caps are highly interesting features of Mars and have received much recent attention, with new and exciting data on morphology, basal units and layered outcroppings. We have examined the climatological, glaciological and geological issues associated with a subsurface exploration of the Mars North Polar Cap and have determined that a fine-scale optical examination of ice in a borehole, to study the stratigraphy, geochemistry and geochronology of the ice, is feasible. This information will enable reconstruction of the development of the cap as well as understanding the properties of its ice. We present visible imagery taken of dust inclusions in archived Greenland ice cores as well as in situ images of accreted lithologic inclusions in West Antarctica, and we argue for use of this kind of data for Mars climate reconstruction as has been successful with Greenland and Antarctic ice-core analysis.

Formation and character of an ancient 19-m ice cover and underlying trapped brine in an "ice-sealed" east Antarctic lake.

Lake Vida, one of the largest lakes in the McMurdo Dry Valleys of Antarctica, was previously believed to be shallow (<10 m) and frozen to its bed year-round. New ice-core analysis and temperature data show that beneath 19 m of ice is a water column composed of a NaCl brine with a salinity seven times that of seawater that remains liquid below -10 degrees C. The ice cover thickens at both its base and surface, sealing concentrated brine beneath. The ice cover is stabilized by a negative feedback between ice growth and the freezing-point depression of the brine. The ice cover contains frozen microbial mats throughout that are viable after thawing and has a history that extends to at least 2,800 (14)C years B.P., suggesting that the brine has been isolated from the atmosphere for as long. To our knowledge, Lake Vida has the thickest subaerial lake ice cover recorded and may represent a previously undiscovered end-member lacustrine ecosystem on Earth.

Recent Greenland Accumulation Estimated from Regional Climate Model Simulations and Ice Core Analysis*

The accumulation defined as “precipitation minus evaporation” over Greenland has been simulated with the high-resolution limited-area regional climate model HIRHAM4 applied over an Arctic integration domain. This simulation is compared with a revised estimate of annual accumulation rate distribution over Greenland taking into account information from a new set of ice core analyses, based on surface sample collections from the North Greenland Traverse. The region with accumulation rates below 150 mm yr−1 in central-northwest Greenland is much larger than previously assumed and extends about 500 km farther to the south. It is demonstrated that good agreement between modeled and observed regional precipitation and accumulation patterns exists, particularly concerning the location and the values of very low accumulation in the middle of Greenland. The accumulation rates in the northern part of Greenland are reduced in comparison to previous estimates. These minima are connected with a prevailing blocking high over the Greenland ice sheet and katabatic wind systems preventing humidity transports to central Greenland. The model reasonably represents the synoptic situations that lead to precipitation. Maxima of precipitation and accumulation occur at the southwestern and southeastern coasts of Greenland and are connected with cyclonic activity and the main storm tracks around Greenland. The central region of the Greenland ice sheet acts as a blocking barrier on moving weather systems and prohibits cyclones moving from west to east across this region and, thus prevents moisture transports.

Air-snow interactions and atmospheric chemistry.

The presence of snow greatly perturbs the composition of near-surface polar air, and the higher concentrations of hydroxyl radicals (OH) observed result in a greater oxidative capacity of the lower atmosphere. Emissions of nitrogen oxides, nitrous acid, light aldehydes, acetone, and molecular halogens have also been detected. Photolysis of nitrate ions contained in the snow appears to play an important role in creating these perturbations. OH formed in the snowpack can oxidize organic matter and halide ions in the snow, producing carbonyl compounds and halogens that are released to the atmosphere or incorporated into snow crystals. These reactions modify the composition of the snow, of the interstitial air, and of the overlying atmosphere. Reconstructing the composition of past atmospheres from ice-core analyses may therefore require complex corrections and modeling for reactive species.

High-sensitivity measurements of strontium isotopes in polar ice

Abstract Techniques have been developed to measure the isotopic composition and concentration of Sr at sub-nanogram per gram levels in polar snow and ice samples. A 84 Sr spike was used to determine Sr concentrations on a single sample aliquot of a few millilitre. Microlitre scale columns of Sr-Spec resin were used to purify Sr samples. Thermal ionisation mass spectrometry (TIMS) was used to measure the Sr isotopic ratios. A single TIMS measurement of the Sr sample yielded both isotopic composition and concentration after deconvolution of spike and sample spectra. This allows isotopic variations in Sr to be used to identify source regions of crustal dust. Early Holocene and last glacial maximum ice core samples from both Antarctica and Greenland were analysed to demonstrate the applicability of the technique. Sr isotopes were analysed in ∼20 g sized samples of Antarctic early Holocene ice where the concentration was only ∼31 pg g−1. This represents an improvement of two orders of magnitude in sample consumption over previous studies allowing for a much higher time resolution in the analysis of polar ice cores.

General Trends for Bulk Diffusion in Ice and Surface Diffusion on Ice

Experimental measurements of bulk diffusion in ice and surface diffusion on ice were performed using laser resonant desorption (LRD) techniques. Bulk diffusion in ice was examined using ice sandwich structures and continuous source experiments together with LRD depth-profiling analysis. Surface diffusion was monitored using prepare−refill−probe LRD experiments. New experimental results were obtained for the bulk diffusion of NH3 and CH3OH. These species probably exist as hydrates in the ice. The LRD measurements for CH3OH hydrate diffusion, combined with previous results, provide evidence for a vacancy-mediated diffusion mechanism. The diffusion rates for NH3 hydrates are much larger than diffusion rates for H2O self-diffusion in ice and are attributed to the disruption of the ice lattice. LRD prepare−refill−probe experiments revealed that surface diffusion was not measurable for almost all of the species examined on ice. Only butane displayed a measurable surface mobility that was attributed to its unique size and chemical nature. These new measurements of bulk diffusion in ice and surface diffusion on ice should be useful in developing our understanding of kinetic processes in and on ice that are relevant to heterogeneous atmospheric chemistry and ice core analysis.

Indirect relationship between surface water budget and wetland extent

We used a suite of two models: a global climate model, and a hydrological routing scheme, to estimate the changes in the surface water budget and extent of natural wetlands, at the last interglacial (126000 years ago) and at the last glacial maximum (21000 years ago). At both time periods, in northern tropical Africa as well as in northern South America, our simulations exhibit, in many places, an indirect relationship between the surface water budget and the extent of natural wetlands. In relatively moist regions, decreasing (increasing) rainfall and runoff at the last glacial maximum (last interglacial) result in increased (decreased) wetland area due to the reduction (increase) in lake depth. This counter‐intuitive result has never been hypothesized before and may shed a new light on the interpretation of past changes in atmospheric methane, as derived from ice core analyses. It also points to the importance of using a bottom‐up modelling approach in this field of study.

Lithium in Greenland ice cores measured by ion chromatography

AbstractIon chromatography (IC) is a widely used technique for analyzing ice cores for ions like Na+, NH4+, K+, Mg2+, Ca2+, F–, MSA–, Cl–, NO2– and SO42– 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 cores is derived from mineral dust. However, data from the NorthGRIP ice core representing the 8.2 kyr BPHolocene 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.