ALBERT

Description: The geographical distribution of firn temperature, annual accumulation rate as well as deuterium and oxygen-18 content in the firn were determined along an east-west transect through central Greenland. This study is based on isotopic and chemical analyses of shallow firn cores at 18 sites along the EGIG line and high-precision firn-temperature measurements m 17 steam-drilled boreholes along the eastern part of the transect. The firn temperatures at 15 m depth range from -31.6°C at Dome GRIP (3230 m a.s.l.) to -11.4°C at Caecilia Nunatak (eastern ice margin at 1600 m a.sl.) and -18°C at T05 (near the western ice margin at 1900 m a.s.l.). The temperature/altitude gradient changes from -0.7°C (100 m)−1in the ice divide region to -1.1 °C (100 m)−1in the eastern part of the dry-snow zone. The temperature/latitude gradient in the central part of the EGIG line is -0.7° C lat−1The average annual accumulation decreases significantly from the west (~47 cm a−1water equivalent at T05) towards the ice divide (20–25 cm a−1water equivalent from T99 to T43). Accumulation rates are constantly low east of the ice divide (−23–17 cm a−1water equivalent), thus dividing central Greenland into two climatologically different regions. The average δ18O and δD values along the whole EGIG line reflect the well-known temperature-dependence for Greenland very well (e.g. ∂18O/∂Tm= 0.69%ₒ °C–1Different regression lines for the western and eastern part, however, should be applied. Unlike the mean annual temperature, the isotopic minimum along the EGIG line lies east of the ice divide. This geographical distribution supports the choice of different water-vapour trajectories in central Greenland for the west and for the east. Significant parts of the water precipitated over the western slope are attributed to cyclonic systems entering Greenland from the west. The deuterium excess shows no significant geographical trend but a uniform seasonal variation at all sites along the EGIG line, suggesting equal contributions from vapour-source areas of the water precipitated over central Greenland.

Description: The geographical distribution of firn temperature, annual accumulation rate as well as deuterium and oxygen-18 content in the firn were determined along an east-west transect through central Greenland. This study is based on isotopic and chemical analyses of shallow firn cores at 18 sites along the EGIG line and high-precision firn-temperature measurements m 17 steam-drilled boreholes along the eastern part of the transect. The firn temperatures at 15 m depth range from -31.6°C at Dome GRIP (3230 m a.s.l.) to -11.4°C at Caecilia Nunatak (eastern ice margin at 1600 m a.sl.) and -18°C at T05 (near the western ice margin at 1900 m a.s.l.). The temperature/altitude gradient changes from -0.7°C (100 m)−1 in the ice divide region to -1.1 °C (100 m)−1 in the eastern part of the dry-snow zone. The temperature/latitude gradient in the central part of the EGIG line is -0.7° C lat−1 The average annual accumulation decreases significantly from the west (~47 cm a−1 water equivalent at T05) towards the ice divide (20–25 cm a−1 water equivalent from T99 to T43). Accumulation rates are constantly low east of the ice divide (−23–17 cm a−1 water equivalent), thus dividing central Greenland into two climatologically different regions. The average δ18O and δD values along the whole EGIG line reflect the well-known temperature-dependence for Greenland very well (e.g. ∂18O/∂Tm = 0.69%ₒ °C–1 Different regression lines for the western and eastern part, however, should be applied. Unlike the mean annual temperature, the isotopic minimum along the EGIG line lies east of the ice divide. This geographical distribution supports the choice of different water-vapour trajectories in central Greenland for the west and for the east. Significant parts of the water precipitated over the western slope are attributed to cyclonic systems entering Greenland from the west. The deuterium excess shows no significant geographical trend but a uniform seasonal variation at all sites along the EGIG line, suggesting equal contributions from vapour-source areas of the water precipitated over central Greenland.

Description: In a snow pit, incorporating about 2.5 a of accumulation, on the 4 450 m high Colle Gnifetti, Monte Rosa, various snow characteristics, isotopes (δ18O, 3H), electrical conductivity, dust, trace elements, and pollen were investigated. The aim of this study was to develop a key for the stratigraphic interpretation of cores from cold, high-alpine firn areas. It appears that the strong influence of wind results in mixing and re-sedimentation processes in the surface layers. Nevertheless, by interpreting several parameters in a combined way, it is possible to classify a large number of the layers according to their season and sometimes to their place of origin. Apart from the melt layers, which only appear in early summer to summer layers, other prominent features are the (Saharan) dust falls, characterized by dust and conductivity peaks.

Description: In a snow pit, incorporating about 2.5 a of accumulation, on the 4 450 m high Colle Gnifetti, Monte Rosa, various snow characteristics, isotopes (δ 18O, 3H), electrical conductivity, dust, trace elements, and pollen were investigated. The aim of this study was to develop a key for the stratigraphic interpretation of cores from cold, high-alpine firn areas. It appears that the strong influence of wind results in mixing and re-sedimentation processes in the surface layers. Nevertheless, by interpreting several parameters in a combined way, it is possible to classify a large number of the layers according to their season and sometimes to their place of origin. Apart from the melt layers, which only appear in early summer to summer layers, other prominent features are the (Saharan) dust falls, characterized by dust and conductivity peaks.

Description: The accumulation and distribution of the 2H content of near-surface layers in the eastern part of the Ronne Ice Shelf were determined from 16 firn cores drilled to about 10 m depth during the Filchner IIIa and IV campaigns in 1990 and 1992, respectively. The cores were dated stratigraphically by seasonal δ2H variations in the firn. In addition, 3H and high-resolution chemical profiles were used to assist in dating. Both the accumulation rate and the stable-isotope content decrease with increasing distance from the ice edge: the δ2H values range from about 195‰ at the ice edge to -25‰ at BAS sites 5 and 6, south of Henry Ice Rise, and the accumulation rates from about 210 to 90 kgm-2 a-1. The δ2H values of the near-surface firn and the 10 m firn temperatures (Θ) at individual sites are very well correlated: dδ2H/dΘ = (10.3 ± 0.6)‰K-1; r = 0.97. The δ2H profiles of the two ice cores BI3 and BI5 drilled in 1990 and 1992 to 215 and 320 m depth, respectively, reflect the gradual depletion in 2H in the firn upstream of the drill sites. Comparison with the surface data indicates that the ice above 142 m in core BIS and above 137 m in core BI3 was deposited on the ice shelf, whereas the deeper ice, down to 152.8 m depth, most probably originated from the margin of the Antarctic ice sheet.

Description: With the intention of contributing to a better understanding of snow depth profiles used in reconstructing the southern hemisphere nitrate background we have measured C1−, , and in firn cores from two coastal Antarctic locations (GvN = Ekströmisen 70°S, 8°W, and Filchner = Filchner-Ronne Ice Shelf 79°S, 57°W). The depth resolution chosen is 2 cm per sample (i.e. 36 and 14 samples per year, respectively).The isotopie composition of the firn cores was concurrently measured, with equally high resolution (deuterium and 18O data, W. Graf, private communication). The GvN core yields an average accumulation rate of 35 cm H2O per year during the period 1979–86, while the Filchner core gives 14 cm H2O per year during the period 1955-80. The net snow accumulation being relatively high allows precise determination of the year to year boundaries, as well as the relative contribution of individual seasons to the total net accumulation. This was achieved by combining the stable isotope data with the chemical tracers nss-sulfate (high concentration in summer) and sea salt (high C1− in autumn and winter). For the two individual locations this procedure allowed assessment of the glacial nitrate concentration seasonality as well as comparing the yearly nitrate deposition.The Filchner location shows a distinct seasonality with maximum concentrations in summer. For nearly half of the years covered we also find higher concentrations in winter. This higher nitrate in winter is always accompanied by high sea salt concentrations. We suggest therefore a mechanism making sea salt aerosol an additional deposition pathway for nitrate in winter. This means that we are not able to link the enhanced winter nitrate deposition to stratospheric denitrification directly. The GvN core does not show significant seasonality. This is presumably due to frequent snow drift events preventing signal conservation.Although the individual accumulation rates differ by a factor of 2.5 the yearly nitrate deposition is in the same range (4-11 kg (km-2 a-1) at both sites. This is caused by the different seasonal modulation of the net snow accumulation. At GvN low nitrate autumn precipitation prevails and keeps the yearly nitrate level constantly low (18-22 ppb). At Filchner, however, a high contribution of summer snow brings the yearly concentration average up to about 30–70 pbb.

Description: By chemical analysis of the upper 40 m of a 124 m ice core from a high-altitude Alpine glacier (Colle Gnifetti, Swiss Alps; 4450 m a.s.l.), records of mineral dust, pH, melt-water conductivity, nitrate and sulfate are obtained. The characteristics of the drilling site are discussed, as derived from glacio-meteorological and chemical analysis. As a consequence of high snow-erosion rates (usually during the winter months), annual snow accumulation is dominated by summer precipitation. Clean-air conditions prevail even during summer; however, they are frequently interrupted by polluted air masses or by air masses which are heavily loaded with desert dust. Absolutely dated reference horizons for Saharan dust, together with the position of the broad nuclear-weapon tritium peak, provide the time-scale for the following statements: (1) Since at least the turn of the century the background melt-water conductivity has been rising steadily, as has the mean snow acidity. The trend of increasing background conductivity at Colle Gnifetti (1.9μS/cm around the beginning of this century, and at present 3.4 μS/cm) is found to be comparable with the records of mean melt-water conductivity reported from ice cores from the Canadian High Arctic. (2) Sulfate and nitrate concentrations are higher by a factor of 4–5 than they were at the beginning of the century. This is to be compared with the two- to three-fold rise in the concentrations in south Greenland during about the same time span.

Description: The accumulation and distribution of the 2H content of near-surface layers in the eastern part of the Ronne Ice Shelf were determined from 16 firn cores drilled to about 10 m depth during the Filchner IIIa and IV campaigns in 1990 and 1992, respectively. The cores were dated stratigraphically by seasonal δ2H variations in the firn. In addition, 3H and high-resolution chemical profiles were used to assist in dating. Both the accumulation rate and the stable-isotope content decrease with increasing distance from the ice edge: the δ2H values range from about 195‰ at the ice edge to -25‰ at BAS sites 5 and 6, south of Henry Ice Rise, and the accumulation rates from about 210 to 90 kgm-2 a-1. The δ2H values of the near-surface firn and the 10 m firn temperatures (Θ) at individual sites are very well correlated: dδ2H/dΘ = (10.3 ± 0.6)‰K-1; r = 0.97.The δ2H profiles of the two ice cores BI3 and BI5 drilled in 1990 and 1992 to 215 and 320 m depth, respectively, reflect the gradual depletion in 2H in the firn upstream of the drill sites. Comparison with the surface data indicates that the ice above 142 m in core BIS and above 137 m in core BI3 was deposited on the ice shelf, whereas the deeper ice, down to 152.8 m depth, most probably originated from the margin of the Antarctic ice sheet.

Description: By chemical analysis of the upper 40 m of a 124 m ice core from a high-altitude Alpine glacier (Colle Gnifetti, Swiss Alps; 4450 m a.s.l.), records of mineral dust, pH, melt-water conductivity, nitrate and sulfate are obtained. The characteristics of the drilling site are discussed, as derived from glacio-meteorological and chemical analysis. As a consequence of high snow-erosion rates (usually during the winter months), annual snow accumulation is dominated by summer precipitation. Clean-air conditions prevail even during summer; however, they are frequently interrupted by polluted air masses or by air masses which are heavily loaded with desert dust.Absolutely dated reference horizons for Saharan dust, together with the position of the broad nuclear-weapon tritium peak, provide the time-scale for the following statements:(1) Since at least the turn of the century the background melt-water conductivity has been rising steadily, as has the mean snow acidity. The trend of increasing background conductivity at Colle Gnifetti (1.9μS/cm around the beginning of this century, and at present 3.4 μS/cm) is found to be comparable with the records of mean melt-water conductivity reported from ice cores from the Canadian High Arctic.(2) Sulfate and nitrate concentrations are higher by a factor of 4–5 than they were at the beginning of the century. This is to be compared with the two- to three-fold rise in the concentrations in south Greenland during about the same time span.

Description: With the intention of contributing to a better understanding of snow depth profiles used in reconstructing the southern hemisphere nitrate background we have measured C1−, , and in firn cores from two coastal Antarctic locations (GvN = Ekströmisen 70°S, 8°W, and Filchner = Filchner-Ronne Ice Shelf 79°S, 57°W). The depth resolution chosen is 2 cm per sample (i.e. 36 and 14 samples per year, respectively). The isotopie composition of the firn cores was concurrently measured, with equally high resolution (deuterium and 18O data, W. Graf, private communication). The GvN core yields an average accumulation rate of 35 cm H2O per year during the period 1979–86, while the Filchner core gives 14 cm H2O per year during the period 1955-80. The net snow accumulation being relatively high allows precise determination of the year to year boundaries, as well as the relative contribution of individual seasons to the total net accumulation. This was achieved by combining the stable isotope data with the chemical tracers nss-sulfate (high concentration in summer) and sea salt (high C1− in autumn and winter). For the two individual locations this procedure allowed assessment of the glacial nitrate concentration seasonality as well as comparing the yearly nitrate deposition. The Filchner location shows a distinct seasonality with maximum concentrations in summer. For nearly half of the years covered we also find higher concentrations in winter. This higher nitrate in winter is always accompanied by high sea salt concentrations. We suggest therefore a mechanism making sea salt aerosol an additional deposition pathway for nitrate in winter. This means that we are not able to link the enhanced winter nitrate deposition to stratospheric denitrification directly. The GvN core does not show significant seasonality. This is presumably due to frequent snow drift events preventing signal conservation. Although the individual accumulation rates differ by a factor of 2.5 the yearly nitrate deposition is in the same range (4-11 kg (km-2 a-1) at both sites. This is caused by the different seasonal modulation of the net snow accumulation. At GvN low nitrate autumn precipitation prevails and keeps the yearly nitrate level constantly low (18-22 ppb). At Filchner, however, a high contribution of summer snow brings the yearly concentration average up to about 30–70 pbb.