Greenland Snow Research Articles

Siderophile metal fallout to Greenland from the 1991 winter eruption of Hekla (Iceland) and during the global atmospheric perturbation of Pinatubo

Ir and Pt are siderophile elements that are considered proxies of meteoric material of cosmic origin entrapped within polar ice layers. However, volcanic and anthropogenic fallouts have the potential to perturb their characteristic extraterrestrial signature even in remote polar areas. Here we show a record of Ir and Pt concentrations in snow samples collected from a 2.7 m pit, which was dug at Summit (Central Greenland), and covered five years from winter 1991 to summer 1995. A well-defined peak of Pt, and a spike of Ir, were found at the base of the snow pit record. These maxima occur in close concurrence with large concentration peaks in Al, Ag, Cd and Hg. Dating of the snow layers together with some geochemical evidence suggests that these peaks originated from the fallout to Greenland of volcanic ash emitted by the nearby Hekla volcano (Iceland), during the eruption of January–March 1991. Interestingly, an anomalous peak of methane sulfonic acid (MSA) in Greenland snow also corresponds to the Hekla ash fallout. This might point to an early biomass production in the North Atlantic Ocean during the first half of 1991, which was possibly stimulated by the fertilizing action of the Hekla ash fallout to seawater. During the following years (1992–1995) the global atmosphere was under the influence of the large perturbation produced by the eruption of Mt. Pinatubo (Philippines) in June 1991. Relatively high Ir and Pt concentrations with super-chondritic ratios are recorded especially during summer 1993. We discuss if this can be interpreted as the possible stratospheric input of Pinatubo's aerosol or fallout of extraterrestrial origin. During the same period the snow pit record was also influenced by the advection of air masses enriched in Pt with respect to Ir. One possibility is that this additional Pt contribution originated from widespread emissions into the troposphere produced by vehicles equipped with catalytic converters. In any case, Pt concentration levels found in recent Greenland snow are about two orders of magnitude lower than previously thought, pointing to a much lower anthropogenic contamination of the Arctic regions from Pt. This challenges the concept of an important hemispheric contamination of Pt from vehicles equipped with catalytic converters.

Seasonal δ 34S variations in two high elevation snow pits measured by 33S– 36S double spike thermal ionization mass spectrometry

δ 34S and sulfate concentrations were determined in snow pit samples using a thermal ionization mass spectrometric technique capable of 0.2‰ accuracy and requires ≈5 μg (0.16 μmol) natural S. The technique utilizes a 33S– 36S double spike for instrumental mass fractionation correction, and has been applied to snow pit samples collected from the Inilchek Glacier, Kyrgyzstan and from Summit, Greenland. These δ 34S determinations provide the first high-resolution seasonal data for these sites, and are used to estimate seasonal sulfate sources. Deuterium (δD) and oxygen (δ 18O) isotope data show that the Inilchek and Summit snow pit samples represent precipitation over ≈20 months. The δ 34S values for the Inilchek ranged from +2.6 ± 0.4‰ to +7.6 ± 0.4‰ on sample sizes ranging from 0.3 to 1.8 μmol S. δ 34S values for Greenland ranged from +3.6 ± 0.7‰ to +13.3 ± 5‰ for sample sizes ranging from 0.05 to 0.29 μmol S. The SO 4 2 - concentration ranged from 92.6 ± 0.4 to 1049 ± 4 ng/g for the Inilchek and 18 ± 9 to 93 ± 6 ng/g for the Greenland snow pit. Anthropogenic sulfate dominates throughout the sampled time interval for both sites based on mass balance considerations. Additionally, both sites exhibit a seasonal signature in both δ 34S and SO 4 2 - concentration. The thermal ionization mass spectrometric technique has three advantages compared to gas source isotopic methods: (1) sample size requirements of this technique are 10-fold less permitting access to the higher resolution S isotope record of low concentration snow and ice, (2) the double spike technique permits δ 34S and S concentration to be determined simultaneously, and (3) the double spike is an internal standard.

Particulate and water‐soluble carbon measured in recent snow at Summit, Greenland

Water‐soluble organic carbon (WSOC), water‐insoluble particulate organic carbon (WIOC), and particulate elemental carbon (EC) were measured simultaneously for the first time on the Greenland Ice Sheet in surface snow and in a 3‐meter snow pit. Snow pit concentrations reveal that, on average, WSOC makes up the majority (89%) of carbonaceous species, followed by WIOC (10%) and EC (1%). The enhancement of OC relative to EC (ratio 99:1) in Greenland snow suggests that, along with atmospheric particulate matter, gaseous organics contribute to snow‐phase OC. Comparison of summer surface snow concentrations in 2006 with past summer snow pit layers (2002–2005) found a significant depletion in WSOC (20–82%) and WIOC (46–65%) relative to EC for 3 of the 4 years. The apparent substantial loss of WSOC and WIOC in aged snow suggests that post‐depositional processes, such as photochemical reactions, need to be considered in linking ice core records of organics to atmospheric concentrations.

A 150-year Record of Heavy Metals in the Varved Sediments of Lake Bolterskardet, Svalbard

Laminated sediments from Bolterskardet Lake on Svalbard provide a new 150-year record of heavy metals in the Arctic. Independent data of 137Cs and 210Pb indicate that these laminations are annually deposited varves. The high sedimentation rate and varved sediments make Lake Bolterskardet a good site for studying history of heavy metal pollution in the region. A suite of heavy metals (Pb, As, Cd , Cu, Cr, Co, Ni, and Sn) were studied. The variations of Cu, Cr, Co, and Ni concentrations show an inverse pattern with the median grain size. It suggests that the particle size has a significant role in the accumulation and enrichment of heavy metals in the sediments. In the concentration profiles of studied heavy metals, only Pb concentrations show a significant increase from the lower parts to the upper parts of the core. Profiles of “total,” “lithogenic,” and “anthropogenic” Pb flux also show an increasing pattern. Anthropogenic Pb flux varies between 0.1 μg cm−2 yr−1 and 12.3 μg cm−2 yr−1, with a mean value of 2.4 μg cm−2 yr−1. The anthropogenic Pb fluxes were relatively low at around 0.7 μg cm−2 yr−1 prior to 1945, slowly increased after 1945, and reached a sidestep (between 1940s and 1970s) with mean value of 1.8 μg cm−2 yr−1. Second high value period was between 1980s and 1990s with mean value of 5.9 μg cm−2 yr−1. The variation of anthropogenic Pb fluxes before 1970 in Bolterskardet Lake coincides with the sulfate record and Pb concentration data from Greenland snow and ice, and the acidity concentration in the Svalbard ice cores. However, the anthropogenic Pb fluxes during the last two decades show a rapidly increasing trend. This regional pattern may suggest that local source is an important factor for heavy metal contamination in Svalbard, and the complex of long-range transport contaminations for regional and global process.

Observation and characterization of radar backscatter over Greenland

Characterization of the microwave signature of the Greenland snow surface enables delineation of the different snow facies and is a tool for tracking the effects of climate change. A new empirical observation model is introduced that uses a limited number of parameters to characterize the snow surface based on the dependence of radar backscatter on incidence angle, azimuth angle, spatial gradient, and temporal rate of change. The individual model parameters are discussed in depth with examples using data from the NASA Scatterometer (NSCAT) and from the C-band European Remote Sensing (ERS) satellite Advanced Microwave Instrument in scatterometer mode. The contribution of each model term to the overall accuracy of the model is evaluated. The relative contributions of the modeled dependencies vary by region. Two studies illustrating applications of the model are included. First, interannual changes over the Greenland ice sheet are investigated using nine years of ERS data. Surface changes are observed as anomalies in the /spl sigma//spl deg/ model parameters. Second, intraannual variations of the surface are investigated. These changes are observed in the average backscatter normalized to a given observation geometry. The results indicate that the model can be used to obtain a more complete understanding of multiyear change and to obtain low-variance high temporal resolution observations of intraannual changes. The model may be applied for increased accuracy in scatterometer, synthetic aperture radar (SAR), and wide-angle SAR studies.

Long range transport of biomass aerosol to Greenland: Multi-spectroscopic investigation of particles deposited in the snow

Results are given from the NIST component of a pilot (“winter-over”) study of seasonal patterns of natural and anthropogenic species in air and snow transported to Summit, Greenland. Central to this research is the quantitative apportionment of fossil and biomass particulate carbon, based on advanced (micromolar) 14C accelerator mass spectrometry (AMS) applied to remote snow samples containing as little as 9 µg C/kg. The measurements were made practicable through stringent attention to the nature and sources of the isotopic-chemical blank, resulting in a blank reduction from »5 µg C to <0.5 µg C. An important result of this work is the first evidence of a seasonal pattern in biomass-C particles in Greenland snow. Although 14C AMS data serve to resolve fossil and biomass carbon quantitatively, a deeper understanding of the aerosol sources and character demands a multidisciplinary approach. This is illustrated with “multi-spectrometric” macro- and micro-analytical data for two cases involving substantial incursions of biomass aerosol to the Summit, Greenland snow.

Atmospheric circulation and cyclone frequency variations linked to the primary modes of Greenland snow accumulation

Data from 34 Greenland firn cores, extending from 1982 to 1996, are used to identify spatial accumulation variability patterns and their associated atmospheric circulation and cyclone frequencies. The first principal component, representing west‐central Greenland accumulation, is correlated to NAO variability, having increased southwesterly (northeasterly) flow over that area during high (low) accumulation winters. The flow is linked to a relative increase in cyclone activity on the west central region of the ice sheet during high accumulation periods. The second principal component represents accumulation over southeastern Greenland where strong westerly flow leads to high accumulation and an increase in lee cyclones on the east and southeast coast. The study provides evidence that increased cyclone activity occurs over, or immediately adjacent to, areas experiencing anomalously high accumulation and it is important to distinguish lee cyclones from “Icelandic” cyclones, as they produce opposite precipitation effects over the ice sheet.

Seasonal variations in N and O isotopes of nitrate in snow at Summit, Greenland: Implications for the study of nitrate in snow and ice cores

Nitrogen and oxygen isotopes of NO3− have been measured in snow and firn from Summit, Greenland. The 15N/14N and 18O/16O ratios of NO3− in recently fallen snow are similar to those of surface snow. Diurnal variation is observed in 15N/14N of NO3−, and possibly 18O/16O, suggesting fractionating loss of NO3− from snow during the day, which is subsequently recovered at night. A larger seasonal variation is observed, with higher 15N/14N and lower 18O/16O of NO3− in summer than winter, which cannot be explained by postdepositional fractionation. The generally high 18O/16O of NO3− in Greenland snow (δ18O versus VSMOW = 65.2 to 79.6‰) indicates that oxygen atoms from ozone have been incorporated into NOx that was subsequently deposited as HNO3. The lower mean δ18O of NO3− in summer snow relative to winter (68.9‰ in summer 2000 and 70.5‰ in summer 2001 versus 77.5‰ in winter 2000–01) is a result of summertime HNO3 production via NO2 reaction with hydroxyl radical (OH), which dilutes the high δ18O imparted on NO2 from ozone. The higher mean 15N/14N of NO3− observed in snow from spring (δ15N versus air N2 = +5.9‰ in 2000 and −1.4‰ in 2001) and summer (+0.1‰ in 2000 and −0.8‰ in 2001) than fall (−9.2‰ in 2000) and winter (−10.0‰ in 2000–01) is more difficult to explain with seasonal photochemistry, given current knowledge. The seasonal 15N/14N change may reflect NOx sources, with a greater fall and wintertime contribution from fossil fuel emissions relative to other inputs of NOx (i.e., biogenic soil emissions, biomass burning, and lightning).

Seasonal variations of heavy metals in central Greenland snow deposited from 1991 to 1995.

To better assess the seasonality in the fallout of heavy metals to central Greenland, a continuous series of 68 snow samples has been collected at a remote site in the Summit area from a 2.7 m pit using ultraclean sampling procedures. This covers a continuous four year time period from spring 1991 to spring 1995. Co, Cu, Zn, Mo, Rh, Pd, Ag, Cd, Sb, Pt, Pb, Bi and U were determined using ultrasensitive inductively coupled plasma sector field mass spectrometry under clean room conditions. In addition we also determined Al by graphite furnace atomic absorption spectrometry and Na+, Ca2+, SO4(2-), MSA and oxalate by ion chromatography, species that will assist in the interpretation of the trace metal data. The data show pronounced inter- and intra-annual variations, with large differences in the amplitude of these variations for the element studied, with few clear seasonality patterns. Generally, high concentrations are observed in the spring snow layers, while much lower concentrations are typical of summer snow layers. Significant correlations are observed between Co, Cu, Zn, Ag and Sb, while Pt, Pd and Rh show no correlation with the other metals. Crustal enrichment factors show that while the crustal dust contribution is probably important for some metals for part of the year (spring), anthropogenic inputs are as important in many instances. Pronounced intra-annual variations are observed for some metals, in particular Pt. The variations observed for this metal parallel fairly closely changes in Russian Pt production, which points to emissions from smelters in the Russian Arctic as likely sources for Pt.

Seasonally resolved Alpine and Greenland ice core records of anthropogenic HCl emissions over the 20th century

The continuous highly resolved records of Cl−, Na+, and Ca2+ in ice cores from Col du Dôme (4250 m elevation, French Alps) and Summit (3240 m elevation, central Greenland) are used to reconstruct the history of atmospheric HCl pollution over Europe and Greenland since the early 20th century. The evaluation of the HCl amount in summer snow deposits at high‐elevation Alpine sites is complex since continental emissions (soils, halide evaporites, and possibly manure‐fertilized fields) account for 80% of the chloride budget and only one fifth of Cl− is related to HCl. During the preindustrial era the HCl content of summer Alpine snow layers fluctuated between 0 and 6 ng g−1, likely in relation with a highly variable interannual biomass burning activity in western Europe. From 1925 to 1960 the HCl levels were slightly higher (3–9 ng g−1), mainly due to growing coal burning emissions in western Europe. In the late 1960s a sharp increase of HCl levels (up to 17 ng g−1) took place as a result of the setup of waste incineration in western Europe, this process contributing 3–4 times more than coal combustion to the HCl budget of summer Alpine snow layers deposited between 1970 and 1990. In winter, sea spray emissions dominate (∼78%) the total Cl− level of Alpine snow layers. The HCl trend in these snow layers remained limited to ∼2 ng g−1 over the 20th century, likely in relation to waste incineration after 1965. In Greenland snow layers most of particulate Cl− originates from sea spray, 1/3 to 2/3 of Cl− being present as HCl in spring and summer, respectively. The Greenland HCl ice core records indicate a preindustrial HCl level close to 4 ng g−1, which is found to be mainly due to the sea‐salt dechlorination, while the contribution of passive volcanic HCl emissions at high northern latitudes can be neglected. The input from sea‐salt dechlorination has been enhanced by a factor of 2–3 during the second half of the 20th century similarly to the increase of the atmospheric acidity in response to growing NOx and SO2 anthropogenic emissions.

Fast nitrogen oxide photochemistry in Summit, Greenland snow

During the 1999 summer field season at Summit, Greenland, we conducted several series of experiments to follow up on our 1998 discovery that NO x is released from the sunlit snowpack. The 1999 experiments included measurements of HONO in addition to NO and NO 2, and were designed to confirm, for Greenland snow, that the processes producing reactive nitrogen oxides in the snow are largely photochemical. Long duration experiments (up to 48 h) in a flow-through chamber and in the natural snowpack revealed sun-synchronous diurnal variations of all three reactive nitrogen oxides. In a second set of experiments we alternately shaded or exposed snow (again in the natural snowpack and in the chamber) to ambient sunlight for short periods to reduce any temperature changes during variations in light intensity. All three N oxides increased (decreased) very rapidly when sunlit (shaded). In all experiments NO 2 was approximately 3-fold more abundant than NO and HONO (which were at similar levels). Higher concentrations of NO 3 − in the snow resulted in higher mixing ratios of HONO, NO and NO 2 in the snow pore air, consistent with our hypothesis that photolysis of NO 3 − is the source of the reactive N oxides.

Gain of the AVHRR visible channel as tracked using bidirectional reflectance of Antarctic and Greenland snow

The snow surfaces of the high plateaus of the East Antarctic and Greenland ice sheets are used to determine multi-year drift in the sensitivity of the visible channel of the Advanced Very High Resolution Radiometer (AVHRR) on the polar-orbiting satellites NOAA-9, 10, and 11. Bidirectional reflectance distribution functions are empirically derived for the months of October-February (Antarctica) and April-August (Greenland) using a simplified atmospheric model. The bidirectional reflectance of the snow surface should not change from year to year for near-nadir satellite views. Therefore, drift in the derived bidirectional reflectance distribution function is interpreted as drift in channel sensitivity. Several factors make the snow surface of an ice sheet suitable as a calibration target for visible and near-UV channels. (1) In this spectral region, snow has a very high albedo (> 97%) that is invariant with grain size and incidence angle. (2) On the high plateaus the temperatures are always far below freezing so the surface consists of cold fine-grained snow, and there is negligible contamination. (3) The ice sheet surfaces are uniform and flat across large areas. (4) Ozone is the only significant variable absorber in this spectral region, and its absorption can be accounted for if the ozone amount is known. (5) Cloud detection and removal is not necessary, because the thin clouds over the high ice sheets apparently do not alter the near-nadir reflectance, as they do over dark surfaces. Our analysis indicates that the visible channel on NOAA-9 degraded linearly over the 3.5-year lifetime of the instrument by 5.3 ± 0.1% per year. NOAA-10 showed non-linear behaviour that could be fitted with a fourth-order polynomial. Data from NOAA-11 prior to the eruption of Mt Pinatubo showed a linear increase in sensitivity of 2.3 ± 0.2% per year. The derived drifts are not sensitive to the choice of spatial and temporal averaging scales, the choice of months and gridboxes, and whether or not a cloud-rejection scheme is used.

Greenland Snow Evidence of Large Scale Atmospheric Contamination for Platinum, Palladium, and Rhodium

Since 1976 in the United States, Canada, and Japan, and later in other countries, the exhaust system of gasoline powered cars has been equipped with catalytic converters containing Pt and/or Pd and/or Rh. This has resulted in a very significant decrease in urban air pollution for various chemical species such as NOx, CO, and hydrocarbons. There has however been concern that their ever increasing use might lead to Platinum Group Metals (PGMs) becoming widely dispersed in the environment. From the analysis of Pt, Pd, and Rh in central Greenland recent snow and ancient ice using the ultrasensitive inductively coupled plasma sector field mass spectrometry technique, we show here that the concentrations of these metals in snow dated from the mid 1990s are indeed approximately 40-120 times higher than in ice dated from 7000 years ago. The fact that such an increase is observed far away from populated areas at a high altitude location indicates there is now a large scale contamination of the troposphere of the Northern Hemisphere for PGMs. Pt/Rh mass ratio in the most recent snow samples is close to the same ratio documented for catalytic converter exhausts in a recent study, which suggests that a large fraction of the recent increase for Pt and Rh might originate from automobile catalytic converters.

Gain of the AVHRR visible channel as tracked using bidirectional reflectance of Antarctic and Greenland snow

Gain of the AVHRR visible channel as tracked using bidirectional reflectance of Antarctic and Greenland snow

Low-level (submicromole) environmental 14C metrology

Accelerator mass spectrometry (AMS) measurements of environmental 14C have been employed during the past decade at the several micromole level (tens of μg carbon), but advanced research in the atmospheric and marine sciences demands still higher (μg) sensitivity, an extreme example being the determination of 14C in elemental or “black” carbon (BC) at levels of 2–10 μg per kg of Greenland snow and ice (Currie et al., 1998). A fundamental limitation for 14C AMS is Poisson counting statistics, which sets in at about 1 μg modern-C. Using the small sample (25 μg) AMS target preparation facility at NOSAMS (Pearson et al., 1998), and the microsample combustion–dilution facility at NIST, we have demonstrated an intrinsic modern-C quantification limit ( m Q) of ca. 0.9 μg, based on a 1-parameter fit to the empirical AMS variance function. (For environmental 14C, the modern carbon quantification limit is defined as that mass ( m Q) corresponding to 10% relative standard deviation (rsd) for the fraction of modern carbon, σ( f M)/ f M.) Stringent control, required for quantitative dilution factors (DL), is achieved with the NIST on-line manometric/mass spectrometry facility that compensates also for unsuspected trace impurities from vigorous chemical processing (e.g., acid digestion). Our current combustion blank is trivial (mean: 0.16 ± 0.02 μg C, n=13) but lognormally distributed (dispersion [σ]: 0.07 ± 0.01 μg). An iterative numerical expression is introduced to assess the quantitative impacts of fossil and modern carbon blank components on m Q; and a new “clean chemistry” BC processing system is described for the minimization of such blanks. For the assay of soot carbon in Greenland snow/ice, the overall processing blank has been reduced from nearly 7 μg total carbon to less than 1 μg, and is undetectable for BC.

Temporal variability of Cd, Pb, and Pb isotope deposition in central Greenland snow

We present a decade‐long (1981–1990) high‐resolution (subseasonal) record of Pb and Cd concentrations and Pb isotopic composition in a series of 119 snow samples from a 6‐m snow pit at Summit, Greenland. Both metals show order of magnitude seasonal variability, with maxima in spring of every year, coinciding with sulfate peaks. These short‐term features complicate attempts to quantify secular decadal‐scale trends associated with anthropogenic source changes (e.g., phasing out of leaded gasoline). A small (&lt;50%) decrease during the decade is estimated for Pb, but no significant trend is observed for Cd. Mean concentrations for the snow pit (Pb = 216, Cd = 11 pmol kg−1) are indistinguishable from mean values for nearly continuous samples of the 1–6 m section of a firn core drilled 1 km away, suggesting freedom from contamination artifact. An evaluation of potential sources confirms that Pb and Cd are dominated by anthropogenic inputs. Isotopic ratios (206Pb/207Pb and 208Pb/207Pb) determined on a subset of snow pit samples of varying ages within the decade indicate that springtime Pb concentration maxima are consistent with a mixture of eastern European, former Soviet Union, and western European sources, while seasonal Pb minima, especially from the early portion of the decade, plot along a different mixing line, suggesting a mixture of U.S. and European sources. The combination of Pb concentration and isotopic composition are consistent with an estimated decrease in U.S. Pb contributions of about twofold over the decade, which predicts a decadal concentration decrease in the snow of ∼30%. However, the secular trends in both concentration and isotopes are barely detectable against seasonal and interannual variability. The evidence for seasonally distinct source regions may be useful for interpretation of high‐resolution records of other chemical species in Greenland snow and ice. Analyses of two deep core sections dated at 1699–1700 and 1780–1788, compared to the snow pit data, indicate that both Pb and Cd deposition in central Greenland roughly doubled during the eighteenth century, then doubled again by the 1980s.

Present Century Record of Organolead Pollution in High Altitude Alpine Snow

Organolead compounds are tracers of lead additives used as anti-knocking agents in leaded gasoline, and snow/ice cores are useful archives of environmental pollution. Determination of these species in those archives provides information on their influence on the Pb pollution by monitoring the changes of organolead concentrations during the years. Organolead compounds have been analyzed by gas chromatography coupled to microwave-induced plasma atomic emission spectrometry (GC−MIP-AES) in a series of snow pit and snow/ice core samples deposited in a high altitude site in the Mont Blanc area between 1956 and 1994. Measured concentrations ranged from 0.1 to 3 pg/g for dimethyllead, from 0.08 to 3.4 pg/g for trimethyllead, from 0.01 to 0.57 pg/g for diethyllead, and from 0.01 to 0.13 pg/g for triethyllead. No organolead compounds were detected in ice deposited before 1962. Concentrations of total alkyllead increased from 1962 till the late 1980s but then declined significantly during the 1990s. Changes in consumption of these species in France were compared with the obtained data. A delay of several years was observed between the restricted consumption of these additives and the subsequent decrease in concentrations observed in the ice. Furthermore, the data were compared with two records for organolead pollution obtained for the Northern Hemisphere: one for Central Greenland snow and the other for vintages originating from the Rhône Valley in southeast France.

Searching for manganese pollution from MMT anti-knock gasoline additives in snow from central Greenland

Mn has been measured in snow core samples dated from 1967 to 1989 collected in central Greenland. Observed concentrations range from 16 to 236 pg g −1. A large fraction of Mn in Greenland snow is found to originate from rock and soil dust. The different possible natural sources for `excess' Mn above that contributed from rock and soil dust include volcanoes, natural vegetation fires and continental biogenic emissions. They could explain part of the observed excess. At least part of it is, however, probably related to anthropogenic inputs, especially from North America. Aside from industrial sources, MMT (methyl-cyclopentadienyl manganese tricarbonyl) anti-knock gasoline additives are good candidates, but our data do not allow to clearly identify their influence. Unambiguous identification will require the direct determination of organo-Mn compounds in comprehensive series of Greenland snow samples with sub-seasonal resolution using highly sensitive speciation techniques.

A forty year record of Mercury in central Greenland snow

Hg has been measured using ultraclean procedures in snow deposited in central Greenland from 1949 to 1989. Concentrations range from ≤0.05 to 2.0 pg/g (mean : 0.43 pg/g), i.e. values which are orders of magnitude lower than those obtained in earlier studies. It indicates that earlier data were plagued by major contamination problems. Combined estimated contributions from natural Hg sources cannot explain Hg concentrations observed in the snow. It suggests that Hg deposition to the Greenland ice sheet is now significantly influenced by anthropogenic inputs from North America, Asia and Europe linked especially to coal burning and solid waste incineration. Although our data suggest that Hg concentrations were higher in snow dated from the late 1940s to the mid 1960s than in more recent snow, further studies are needed to clearly assess Hg temporal trends.

The North Atlantic Oscillation and its imprint on precipitation and ice accumulation in Greenland

Interannual to decadal fluctuations in net precipitation and ice accumulation are examined over Greenland. It is shown that in western Greenland these fluctuations are correlated with the North Atlantic Oscillation. The analysis is based on two complementary data sources: A highly resolved net precipitation and accumulation history over 15 years derived form the reanalysis data of the European Centre for Medium‐Range Weather Forecasts and a composite ice accumulation record representative for the western part of Central Greenland. It is suggested that western Greenland snow accumulation is a good proxy for the NAO index with the potential for the reconstruction of a long time series.