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The Last Interglacial (129–116 thousand years ago (ka)) represents one of the warmest climate intervals of the past 800,000 years and the most recent time when sea level was metres higher than today. However, the timing and magnitude of the peak warmth varies between reconstructions, and the relative importance of individual sources that contribute to the elevated sea level (mass gain versus seawater expansion) during the Last Interglacial remains uncertain. Here we present the first mean ocean temperature record for this interval from noble gas measurements in ice cores and constrain the thermal expansion contribution to sea level. Mean ocean temperature reached its maximum value of 1.1 ± 0.3 °C warmer-than-modern values at the end of the penultimate deglaciation at 129 ka, which resulted in 0.7 ± 0.3 m of thermosteric sea-level rise relative to present level. However, this maximum in ocean heat content was a transient feature; mean ocean temperature decreased in the first several thousand years of the interglacial and achieved a stable, comparable-to-modern value by ~127 ka. The synchroneity of the peak in mean ocean temperature with proxy records of abrupt transitions in the oceanic and atmospheric circulation suggests that the mean ocean temperature maximum is related to the accumulation of heat in the ocean interior during the preceding period of reduced overturning circulation.

The South Pole Ice Core (SPICEcore) was drilled in 2014-2016 to provide a detailed multi-proxy archive of paleoclimate conditions in East Antarctica during the Holocene and late Pleistocene. Interpretation of these records requires an accurate depth-age relationship. Here, we present the SPICEcore (SP19) timescale for the age of the ice of SPICEcore. SP19 is synchronized to the WD2014 chronology from the West Antarctic Ice Sheet Divide (WAIS Divide) ice core using stratigraphic matching of 251 volcanic events. These events indicate an age of 54 302±519 BP (years before 1950) at the bottom of SPICEcore. Annual layers identified in sodium and magnesium ions to 11 341 BP were used to interpolate between stratigraphic volcanic tie points, yielding an annually resolved chronology through the Holocene. Estimated timescale uncertainty during the Holocene is less than 18 years relative to WD2014, with the exception of the interval between 1800 to 3100 BP when uncertainty estimates reach ±25 years due to widely spaced volcanic tie points. Prior to the Holocene, uncertainties remain within 124 years relative to WD2014. Results show an average Holocene accumulation rate of 7.4 cm yr-1 (water equivalent). The time variability of accumulation rate is consistent with expectations for steady-state ice flow through the modern spatial pattern of accumulation rate. Time variations in nitrate concentration, nitrate seasonal amplitude and δ15N of N2 in turn are as expected for the accumulation rate variations. The highly variable yet well-constrained Holocene accumulation history at the site can help improve scientific understanding of deposition-sensitive climate proxies such as δ15N of N2 and photolyzed chemical compounds.

New ice cores retrieved from the Taylor Glacier (Antarctica) blue ice area contain ice and air spanning the Marine Isotope Stage (MIS) 5-4 transition, a period of global cooling and ice sheet expansion. We determine chronologies for the ice and air bubbles in the new ice cores by visually matching variations in gas- and ice-phase tracers to preexisting ice core records. The chronologies reveal an ice age-gas age difference (Δage) approaching 10 ka during MIS 4, implying very low snow accumulation in the Taylor Glacier accumulation zone. A revised chronology for the analogous section of the Taylor Dome ice core (84 to 55 ka), located to the south of the Taylor Glacier accumulation zone, shows that Δage did not exceed 3 ka. The difference in Δage between the two records during MIS 4 is similar in magnitude but opposite in direction to what is observed at the Last Glacial Maximum. This relationship implies that a spatial gradient in snow accumulation existed across the Taylor Dome region during MIS 4 that was oriented in the opposite direction of the accumulation gradient during the Last Glacial Maximum.

In this study, vanillic acid was measured in the Tunu ice core from northeastern Greenland in samples covering the past 1700 years. Vanillic acid is an aerosol-borne aromatic methoxy acid, produced by the combustion of lignin during biomass burning. Air mass trajectory analysis indicates that North American boreal forests are likely the major source region for biomass burning aerosols deposited to the ice core site. Vanillic acid levels in the Tunu ice core range from < 0.005 to 0.08 ppb. Tunu vanillic acid exhibits centennial-scale variability in pre-industrial ice, with elevated levels during the warm climates of the Roman Warm Period and Medieval Climate Anomaly, and lower levels during the cooler climates of the Late Antique Little Ice Age and the Little Ice Age. Analysis using a peak detection method revealed a positive correlation between vanillic acid in the Tunu ice core and both ammonium and black carbon in the North Greenland Eemian Ice Drilling (NEEM) project ice core from 600 to 1200 CE. The data provide multiproxy evidence of centennial-scale variability in North American high-latitude fire during this time period.

Wildfires and their emissions have significant impacts on ecosystems, climate, atmospheric chemistry, and carbon cycling. Well-dated proxy records are needed to study the long-term climatic controls on biomass burning and the associated climate feedbacks. There is a particular lack of information about long-term biomass burning variations in Siberia, the largest forested area in the Northern Hemisphere. In this study we report analyses of aromatic acids (vanillic and para-hydroxybenzoic acids) over the past 2600 years in the Eurasian Arctic Akademii Nauk ice core. These compounds are aerosol-borne, semi-volatile organic compounds derived from lignin combustion. The analyses were made using ion chromatography with electrospray mass spectrometric detection. The levels of these aromatic acids ranged from below the detection limit (0.01 to 0.05 ppb; 1 ppb = 1000 ng L-1) to about 1 ppb, with roughly 30% of the samples above the detection limit. In the preindustrial late Holocene, highly elevated aromatic acid levels are observed during three distinct periods (650-300 BCE, 340-660 CE, and 1460-1660 CE). The timing of the two most recent periods coincides with the episodic pulsing of ice-rafted debris in the North Atlantic known as Bond events and a weakened Asian monsoon, suggesting a link between fires and large-scale climate variability on millennial timescales. Aromatic acid levels also are elevated during the onset of the industrial period from 1780 to 1860 CE, but with a different ratio of vanillic and para-hydroxybenzoic acid than is observed during the preindustrial period. This study provides the first millennial-scale record of aromatic acids. This study clearly demonstrates that coherent aromatic acid signals are recorded in polar ice cores that can be used as proxies for past trends in biomass burning.

Interpretation of ice core trace gas records depends on an accurate understanding of the processes that smooth the atmospheric signal in the firn. Much work has been done to understand the processes affecting air transport in the open pores of the firn, but a paucity of data from air trapped in bubbles in the firn-ice transition region has limited the ability to constrain the effect of bubble closure processes. Here we present high-resolution measurements of firn density, methane concentrations, nitrogen isotopes, and total air content that show layering in the firn-ice transition region at the West Antarctic Ice Sheet (WAIS) Divide ice core site. Using the notion that bubble trapping is a stochastic process, we derive a new parameterization for closed porosity that incorporates the effects of layering in a steady state firn modeling approach. We include the process of bubble trapping into an open-porosity firn air transport model and obtain a good fit to the firn core data. We find that layering broadens the depth range over which bubbles are trapped, widens the modeled gas age distribution of air in closed bubbles, reduces the mean gas age of air in closed bubbles, and introduces stratigraphic irregularities in the gas age scale that have a peak-to-peak variability of ~10 years at WAIS Divide. For a more complete understanding of gas occlusion and its impact on ice core records, we suggest that this experiment be repeated at sites climatically different from WAIS Divide, for example, on the East Antarctic plateau.

The West Antarctic Ice Sheet Divide (WAIS Divide, WD) ice core is a newly drilled, high-accumulation deep ice core that provides Antarctic climate records of the past ~68 ka at unprecedented temporal resolution. The upper 2850 m (back to 31.2 ka BP) have been dated using annual-layer counting. Here we present a chronology for the deep part of the core (67.8-31.2 ka BP), which is based on stratigraphic matching to annual-layer-counted Greenland ice cores using globally well-mixed atmospheric methane. We calculate the WD gas age-ice age difference (Δage) using a combination of firn densification modeling, ice-flow modeling, and a data set of δ15N-N2, a proxy for past firn column thickness. The largest Δage at WD occurs during the Last Glacial Maximum, and is 525 ± 120 years. Internally consistent solutions can be found only when assuming little to no influence of impurity content on densification rates, contrary to a recently proposed hypothesis. We synchronize the WD chronology to a linearly scaled version of the layer-counted Greenland Ice Core Chronology (GICC05), which brings the age of Dansgaard-Oeschger (DO) events into agreement with the U/Th absolutely dated Hulu Cave speleothem record. The small Δage at WD provides valuable opportunities to investigate the timing of atmospheric greenhouse gas variations relative to Antarctic climate, as well as the interhemispheric phasing of the "bipolar seesaw".

Abstract. The West Antarctic Ice Sheet (WAIS)-Divide ice core (WAIS-D) is a newly drilled, high-accumulation deep ice core that provides Antarctic climate records of the past ∼68 ka at unprecedented temporal resolution. The upper 2850 m (back to 31.2 ka BP) have been dated using annual-layer counting. Here we present a chronology for the deep part of the core (67.8–31.2 ka BP), which is based on stratigraphic matching to annual-layer-counted Greenland ice cores using globally well-mixed atmospheric methane. We calculate the WAIS-D gas age-ice age difference (Δage) using a combination of firn densification modeling, ice flow modeling, and a dataset of δ15N-N2, a proxy for past firn column thickness. The largest Δage at WAIS-D occurs during the last glacial maximum, and is 525 ± 100 years. Internally consistent solutions can only be found when assuming little-to-no influence of impurity content on densification rates, contrary to a recently proposed hypothesis. We synchronize the WAIS-D chronology to a linearly scaled version of the layer-counted Greenland Ice Core Chronology (GICC05), which brings the age of Dansgaard-Oeschger (DO) events into agreement with the U/Th absolutely dated Hulu speleothem record. The small Δage at WAIS-D provides valuable opportunities to investigate the timing of atmospheric greenhouse gas variations relative to Antarctic climate, as well as the interhemispheric phasing of the bipolar "seesaw".

Interior Antarctica is among the most remote places on Earth and was thought to be beyond the reach of human impacts when Amundsen and Scott raced to the South Pole in 1911. Here we show detailed measurements from an extensive array of 16 ice cores quantifying substantial toxic heavy metal lead pollution at South Pole and throughout Antarctica by 1889 - beating polar explorers by more than 22 years. Unlike the Arctic where lead pollution peaked in the 1970s, lead pollution in Antarctica was as high in the early 20(th) century as at any time since industrialization. The similar timing and magnitude of changes in lead deposition across Antarctica, as well as the characteristic isotopic signature of Broken Hill lead found throughout the continent, suggest that this single emission source in southern Australia was responsible for the introduction of lead pollution into Antarctica at the end of the 19(th) century and remains a significant source today. An estimated 660 t of industrial lead have been deposited over Antarctica during the past 130 years as a result of mid-latitude industrial emissions, with regional-to-global scale circulation likely modulating aerosol concentrations. Despite abatement efforts, significant lead pollution in Antarctica persists into the 21(st) century.

The 17O excess (Δ170= δΔ17O-0.52×δ18O) of sulfate and nitrate reflects the relative importance of their different production pathways in the atmosphere. A new record of sulfate and nitrate Δ17O spanning the last 2400 years from the West Antarctic Ice Sheet Divide ice core project shows significant changes in both sulfate and nitrate Δ17O in the most recent 200 years, indicating changes in their formation pathways. The sulfate Δ17O record exhibits a 1.1% increase in the early 19th century from (2.4 ± 0.2)% to (3.5 ± 0.2)%, which suggests that an additional 12-18% of sulfate formation occurs via aqueous-phase production by O3, relative to that in the gas phase. Nitrate Δ17O gradually decreases over the whole record, with a more rapid decrease between the mid-19th century and the present day of 5.6%, indicating an increasing importance of RO2 in NOx cycling between the mid-19th century and the present day in the mid- to high-latitude Southern Hemisphere. The former has implications for the climate impacts of sulfate aerosol, while the latter has implications for the tropospheric O 3 production rate in remote low-NOx environments. Using other ice core observations, we rule out drivers for these changes other than variability in extratropical oxidant (OH, O3, RO2, H 2O2, and reactive halogens) concentrations. However, assuming OH, H2O2, and O3 are the main oxidants contributing to sulfate formation, Monte Carlo box model simulations require a large (≥260%) increase in the O3/OH mole fraction ratio over the Southern Ocean in the early 19th century to match the sulfate Δ17O record. This unlikely scenario points to a deficiency in our understanding of sulfur chemistry and suggests other oxidants may play an important role in sulfate formation in the mid- to high-latitude marine boundary layer. The observed decrease in nitrate Δ17O since the mid-19th century is most likely due to an increased importance of RO2 over O3 in NOx cycling and can be explained by a 60-90% decrease in the O 3/RO2 mole fraction ratio in the extratropical Southern Hemisphere NOx-source regions. © Author(s) 2014.

We present a reconstruction of the Greenland Ice Sheet surface mass balance (SMB) from 1870 to 2010, based on merged Twentieth Century Reanalysis (20CR) and European Centre for Medium-Range Weather Forecasts (ECMWF) meteorological reanalyses, and we compare our new SMB series with global and regional climate and atmospheric circulation indices during this period. We demonstrate good agreement between SMB annual series constructed from 20CR and ECMWF reanalyses for the common period of overlap and show statistically significant agreement of long-term modeled snowfall with ice-core-based accumulation data. We analyze variations in SMB for the last 140 years and highlight the periods with significantly increased runoff and decreased SMB since 1870, which have both been enhanced in the period since 1990, as well as interannual variations in SMB linked to Greenland climate fluctuations. We show very good agreement of our SMB series variations with existing, independently derived SMB series (RACMO2) variations for the past few decades of overlap but also a significant disparity of up to ∼200 km3 yr-1 in absolute SMB values due to poorly constrained modeled accumulation reflecting a lack of adequate validation data in southeast Greenland. There is no significant correlation between our SMB time series and a widely referenced time series of North Atlantic icebergs emanating from Greenland for the past century, which may reflect the complex nature of the relationship between SMB and ice dynamical changes. Finally, we discuss how our analysis sheds light on the sensitivity and response of the Greenland Ice Sheet to ongoing and future global climate change, and its contribution to global sea level rise. Copyright 2011 by the American Geophysical Union.

An updated accumulation map for Greenland is presented on the basis of 39 new ice core estimates of accumulation, 256 ice sheet estimates from ice cores and snow pits used in previous maps, and reanalysis of time series data from 20 coastal weather stations. The period 1950-2000 is better represented by the data than are earlier periods. Ice-sheetwide accumulation was estimated based on kriging. The average accumulation (95% confidence interval, or ±2 times standard error) over the Greenland ice sheet is 30.0 ± 2.4 g cm -2 a-1, with the average accumulation above 2000-m elevation being essentially the same, 29.9 ± 2.2 g cm-2 a -1. At higher elevations the new accumulation map maintains the main features shown in previous maps. However, there are five coastal areas with obvious differences: southwest, northwest, and eastern regions, where the accumulation values are 20-50% lower than previously estimated, and southeast and northeast regions, where the accumulation values are 20-50% higher than previously estimated. These differences are almost entirely due to new coastal data. The much lower accumulation in the southwest and the much higher accumulation in the southeast indicated by the current map mean that long-term mass balance in both catchments is closer to steady state than previously estimated. However, uncertainty in these areas remains high owing to strong gradients in precipitation from the coast inland. A significant and sustained precipitation measurement program will be needed to resolve this uncertainty. Copyright 2009 by the American Geophysical Union.

An analysis of 96 snow pit and ice cores distributed over the Greenland ice sheet is used to determine the main drivers of variability in the preserved records of nitrate concentration. The data set provides samples from spatially distributed locations, allowing us to investigate the effect of snow accumulation rate, temperature, and sublimation on nitrate concentration. The mean ice sheet concentration in the dry snow zone (2000 ≥ mean annual sea level (masl)) is 132 ng g-1, ranging between 47 and 265 ng g -1 with a standard deviation of ±37 ng g-1. Nitrate flux varies between 1.1 and 14.7 μg cm-2 a-1 with a mean of 4 ± 2 μg cm-2 a-1. Large-scale spatial variability exists as a result of accumulation gradients, with concentration 5% greater in the northern plateau, yet flux over the northern plateau is 30% lower than the dry snow zone as a whole. While spatially, flux appears to be more dependent on accumulation, preservation of flux shows increasing dependence on concentration with increasing accumulation. The relationship between concentration and accumulation is nonlinear, showing less dependence in the low-accumulation regions versus high-accumulation regions. Accumulation alone is insufficient to account for the observed variability in nitrate flux in the low-accumulation regions, and evidence supports the need for additional components to a transfer function model for nitrate that includes photochemistry, temperature, and sublimation. Spatial variability across the ice sheet is nonuniform, and changes in nitrate concentration have occurred in some regions at a greater rate than others. While the data support that overall the ice sheet acts as an archive of paleoatmospheric concentration despite the effects of postdepositional processing, one needs to consider spatial variables to properly account for trends and variability in the records. This is tested by evaluating past spatial relationships and yields the result that the significant geographic shifts with respect to reactive N concentrations have occurred over the ice sheet in the past century. Copyright 2009 by the American Geophysical Union.

Ice cores collected in 2000 (ITASE 00-1) and 2005 (WDC05A, WDC05Q) from the West Antarctic Ice Sheet Divide (WAIS Divide) project site were used to investigate the spatial and temporal variability in accumulation. The ice cores were dated based on annual layer counting of multiple glaciochemical measurements resulting in bottom depth ages for WDC05A, VVDC05Q, and ITASE 00-1 of 1775, 1521, and 1653 A.D., with mean annual accumulation rates of 0.200, 0.204, and 0.221 mweq a-1, respectively. Small-scale spatial variability (SSV) was determined using an analysis of variance of accumulation in the ice core array, thereby quantifying the uncertainty in individual accumulation records. Results indicate that the spatial variability was 0.030 mweq a-1, or approximately 15% of the average annual accumulation. An accumulation record representative of the WAIS Divide local area over recent centuries was developed using a principal component analysis to identify the coherent accumulation signal. The WAIS Divide local record exhibited 14% interannual variability (1 standard deviation of the mean) with the SSV reduced to 0.017 mweq a-1. Correlations of the WAIS Divide local accumulation record with atmospheric indices (e.g., Antarctic Oscillation) exhibited periods when the records oscillate in and out of phase. Thus, reconstructing local and global atmospheric indices from WAIS Divide accumulation records over recent centuries may prove problematic. Copyright 2008 by the American Geophysical Union.

Annually resolved ice core records from different regions over the Greenland ice sheet (GrIS) are used to investigate the spatial and temporal variability of calcium (Ca2+, mainly from mineral dust) and sodium (Na+, mainly from sea salt) deposition. Cores of high common inter-annual variability are grouped with an EOF analysis, resulting in regionally representative Ca2+ and Na+ records for northeastern and central Greenland. Utilizing a regression and validation method with ERA-40 reanalysis data, these common records are associated with distinct regional atmospheric circulation patterns over the North American Arctic, Greenland, and Central to Northern Europe. These patterns are interpreted in terms of transport and deposition of the impurities. In the northeastern part of the GrIS sea salt records reflect the intrusion of marine air masses from southeasterly flow. A large fraction of the Ca2+ variability in this region is connected to a circulation pattern suggesting transport from the west and dry deposition. This pattern is consistent with the current understanding of a predominantly Asian source of the dust deposited over the GrIS. However, our results also indicate that a significant fraction of the inter-annual dust variability in NE and Central Greenland is determined by the frequency and intensity of wet deposition during the season of high atmospheric dust loading, rather than representing the variability of the Asian dust source and/or long-range transport to Greenland. The variances in the regional proxy records explained by the streamfunction patterns are high enough to permit reconstructions of the corresponding regional deposition regimes and the associated circulation patterns. © Springer-Verlag 2006.

Nitrate records from six Greenland ice cores covering the period 1789 to 1995 show a significant correlation in concentration for averaging periods greater than 10 years, as well as an approximately 60% increase in average concentration during the last 75 years. Annual nitrate fluxes contain low-frequency trends driven primarily by changes in concentration, while higher-frequency variability is driven by changes in snow accumulation. Increases in concentration yield nearly 30% higher nitrate flux (2.5 to 3.2 μg m-2 yr-1) and an 11% increase in variability during the 1895 to 1994 period versus the prior 100 years. Nitrate trends in the cores during the last 100 years are also correlated with global nitrate emissions, with a highly significant average r value of 0.93 for the six cores. During the period of anthropogenic influence, nitrate is positively correlated with the North Atlantic Oscillation, while prior to that the correlation is negative, and less significant, suggesting a link between transport of anthropogenic emissions and the North Atlantic Oscillation. Significant preanthropogenic periodicities identified through singular spectrum analysis show decadal variability in the nitrate record leading to shifts as great as 30% from the mean state but none as great as the anthropogenic-driven deviation. Copyright 2006 by the American Geophysical Union.

We report new century-scale ice core records of hydrogen peroxide (H2O2), a major atmospheric oxidant, from 23 locations across the West Antarctic Ice Sheet (WAIS) and use the spatial variability of (multi-) annual mean H2O2 concentrations in snow and firn to investigate the sensitivity of ice core H2O2 preservation to mean annual temperature and accumulation rate. In agreement with the ice-air equilibrium partitioning, H2O2 uptake in near-surface firn was found to be greatest at low temperatures, while postdepositional losses from degassing increase as accumulation rates decrease. This resulted in almost complete loss of H2O2 at warm (>-25°C), low-accumulation sites (94% deviations from the ice-air equilibrium at high-accumulation sites (>30 cm yr-1), but close-to-equilibrium values on the East Antarctic Plateau, where it is dry ( 0.6, p < 0.05) during extended El Niño-La Niña events and explain the occurrence of significant spectral peaks at ENSO-like periodicities (2-7 years) in the H2O2 record. Core records of H2O2 at high-accumulation sites (>30 cm yr-1) are most suitable for detection of temporal changes in atmospheric concentration, although a long-term H2O2 record will be well preserved under the current environment at the WAIS Divide core site. Copyright 2006 by the American Geophysical Union.

The troposphere above the West Antarctic Ice Sheet (WAIS) was sampled for hydroperoxides at 21 locations during 2-month-long summer traverses from 2000 to 2002, as part of the U.S. International Trans-Antarctic Scientific Expedition (US ITASE). First-time quantitative measurements using a high-performance liquid chromatography method showed that methylhydroperoxide (MHP) is the only important organic hydroperoxide occurring in the Antarctic troposphere and that it is found at levels 10 times those previously predicted by photochemical models. During three field seasons, means and standard deviations for hydrogen peroxide (H2O2) were 321 ± 158 pptv, 650 ± 176 pptv, and 330 ± 147 pptv. While MHP was detected but not quantified in December 2000, levels in summer 2001 and 2002 were 317 ± 128 pptv and 304 ± 172 pptv. Results from firn air experiments and diurnal variability of the two species showed that atmospheric H2O2 is significantly impacted by a physical snow pack source between 76° and 90°S, whereas MHP is not. We show strong evidence of a negative correlation between stratospheric ozone and H2O2 at the surface. Between 27 November and 12 December in 2001, when ozone column densities dropped below 220 Dobson units (DU) (means in 2000 and 2001 were 318 DU and 334 DU, respectively), H2O2 was 1.7 times that observed in the same period in 2000 and 2002, while MHP was only 80% of the levels encountered in 2002. Photochemical box model runs match MHP observations only when the production rate from CH3O2 + HO2 was increased to the upper limit of its estimated range of uncertainty. Model results suggest that NO and OH levels on WAIS are closer to coastal values, while Antarctic Plateau levels are higher, confirming that region to be a highly oxidizing environment. The modeled sensitivity of H2O2 and particularly MHP to NO offers the potential to use atmospheric hydroperoxides to constrain the NO background and thus estimate the past oxidation capacity of the remote atmosphere using ice cores. Copyright 2005 by the American Geophysical Union.

In a yearlong investigation of the air-snow transfer function for nitrate (NO3-) at the Greenland Environmental Observatory, Summit (3203 m above sea level), surface snow concentrations measured every other day were compared with levels measured in 10 snow pits dug adjacent to accumulation stakes. Concentrations in the surface snow ranged from 0.4 to 34 μM with a mean of 2.9 ± 1.9 μM. Measured firn profiles in the snow pits had a maximum NO3- concentration of 12 μM and a mean of 2.7 ± 0.5 μM. Reconstructed profiles from surface snow observations and accumulation data closely matched the observed profiles. The small difference in preserved concentrations from observed surface snow concentrations gives evidence of only 7% postdepositional loss at this site (mean annual accumulation ∼23 g cm-2 yr-1). Removing the three highest outliers (which may originate from local sources) of surface snow concentration drops the mean to 2.7 μM, further demonstrating preservation. Results indicate that at this site accumulation is the most significant process affecting preservation of nitrate in the firm. Other rapid postdepositional processes may impact surface snow concentrations, but do not appear to significantly change the preserved record. The inverse analysis of converting preserved records to surface snow concentrations provides equivalent evidence of the same preservation. Copyright 2004 by the American Geophysical Union.

Interferometric synthetic-aperture radar (InSAR) observations of southeast Greenland glaciers acquired by the Earth Remote Sensing Satellites (ERS-1/2) in 1996 were combined with ice sounding radar data collected in the late 1990s to estimate a total discharge of 46 ± 3 km3 ice per year between 62°N and 66°N, which is significantly lower than a mass input of 29 ± 3 km3 ice per year calculated from a recent compilation of snow accumulation data. Further north, Helheim Glacier discharges 23 ± 1 km3/yr vs 30 ± 3 km3/yr accumulation; Kangerdlugssuaq Glacier discharges 29 ± 2 km3/yr vs 23 ± km3/yr; and Daugaard-Jensen Glacier discharges 10.5 ± 0.6 km3/yr vs 10.5 ± 1 km3/yr. The mass balance of east Greenland glaciers is therefore dominated by the negative mass balance of southeast Greenland glaciers (- 17 ± 4 km3/yr), equivalent to a sea level rise of 0.04 ± 0.01 mm/yr. Warmer and drier conditions cannot explain the imbalance which we attribute to longterm changes in ice dynamics. Copyright 2004 by the American Geophysical Union.

This article presents a study which examined whether the Big 8 accounting firms are increasing their share of the auditing services market for publicly registered companies in the U.S. One cannot refute that Big 8 firms hold a tremendous share of the auditing services market for the largest corporations in the U.S., but a totally different question is whether the Big 8 are expanding their market share dominance by obtaining clients from non-Big 8 firms. The research approach consists of descriptive analyses and tests of significance in direction of observed auditor changes between Big 8 and non-Big 8 firms using the nonparametric McNemar test. The population examined consists of all public companies filing Forms 8-K indicating a change in auditors as reported in the SEC News Digest during the nine years ended in 1982. While the Big 8 clearly audit the preponderance of public companies, another consideration is whether that market share is increasing. The evidence presented in this study suggests that this is so in respect to New York Stock Exchange and American Stock Exchange companies. However, the patterns of audit changes in the numerically larger over the counter audit market indicates considerable switching.