Description: In order to interpret the paleoclimatic record stored in the air enclosed in polar ice cores, it is crucial to understand the fundamental lock-in process. Within the porous firn, bubbles are sealed continuously until the respective horizontal layer reaches a critical porosity. Present-day firn models use a postulated temperature dependence of this value as the only parameter to adjust to the surrounding conditions of individual sites. However, no direct measurements of the firn microstructure could confirm these assumptions. Here we show that the critical porosity is a universal constant by providing a statistically solid data set of µm-resolution 3D X-ray computer tomographic measurements for ice cores representing different extremes of the temperature and accumulation ranges. We demonstrate why indirect measurements yield misleading data and substantiate our observations by applying percolation theory as a theoretical framework for bubble trapping. Incorporation of our results does significantly influence the dating of trace gas records, changing gas age-ice age differences by up to more than 1000 years. This will help resolve inconsistencies, such as differences between East Antarctic d15N records (as a proxy for firn height) and model results. We expect our findings to be the basis for improved firn air and densification models, leading to lower dating uncertainties. The reduced coupling of proxies and surrounding conditions may allow for more sophisticated reinterpretations of trace gas records in terms of paleoclimatic changes and will foster the development of new proxies, such as the air content as a marker of local insolation.

Description: This dataset contains accumulation rates as reconstructed from ice-penetrating radar. The radar data were acquired during a traverse in 2007 and are from a 250MHz ground-penetrating radar. Accumulation rates were reconstructed using an inverse method where the depth of the radar layers inform on past accumulation rates. The age of the layers were assigned from a previous study by Karlsson et al., 2016 (doi:10.3389/feart.2016.00097).

Description: This dataset contains accumulation rates as reconstructed from ice-penetrating radar. The radar data were acquired during a traverse in 2015 and are from a 250MHz ground-penetrating radar. Accumulation rates were reconstructed using an inverse method where the depth of the radar layers inform on past accumulation rates. The age of the layers were assigned from a previous study by Karlsson et al., 2016 (doi:10.3389/feart.2016.00097).

Description: This data collection contains readings of accumulation stake along the approximately 800 km long traverse route Neumayer-Kottas-Kohnen, Dronning Maud Land, Antarctica. By comparing the readings of an individual stake in two different seasons the amount of surface accumulation (i.e. snow deposition) or erosion (e.g. from sublimation of wind scour) can be determined. Stake readings were conducted approximately every year starting from season 1995/1996 to 2005/2006 as part of the European Project for Ice Coring In Antarctica (EPICA). The readings were carried out by a dedicated two to three person team accompanying the traverse from Neumayer station to Kohnen station. The readings were performed by a simple measurement of the visible length of the stake above the snow surface. For tilted stakes, the vertical height above the surface as well as the length of the stake was measured. New stakes were deployed when less than about 1.5 m of the previous stake was visible or a stake was lost (e.g. from breaking off or falling over and finally get burried in snow). Consequently, at some locations more than one stake is visible for several years (e.g. when the average snow accumulation was rather low). In those cases all visible stakes were recorded at the same location of such a stake cluster and added to the table as Height_1, Height 2, Height 3). Positions were measured with a simple GPS with coarse acquisition accuracy (order of several meters to tens of meters), which is sufficiently accurate to separate different stake locations (usually 500 m apart and horizontal displacement smaller than about 150 m/a, with largest displacements on the Ekström ice shelf). In very few cases, empty lines originate from missing stakes and the required position. In very few cases, a second line with the same coordinate corresponds to the same location with a fourth stake deployed as a new stake. From Neumayer station to Kottas camp stakes were deployed at approximately a 500 m interval. As the spatial variation of accumulation on the polar plateau is smaller than in the lower foreland (in this case the Ritscherflya) the stake distances was increased to 1 km to several kilometers from Kottas camp onto the polar plateau to Kohnen station. Additional field comments made by observing personal were removed from the files. However, original field notes in notebooks are available from AWI's Archive for German Polar Research (Oerter et al., 2013). Although surface accumulation is still one of the major unknowns to determine the the total surface mass balance of the Antarctic ice sheet, especially under climate change, direct long-term observations of surface accumulation are still one of the major gaps in field observations (Eisen et al., 2008). This time series of stake readings provides the basis for calculation the change in accumulation in space and time (e.g. Rotschky et al., 2007). It is thus fundamental for a decade-long record of the spatio-temporal characteristics of surface accumulation, which can be put into context to meteorological and oceanographic changes in the region.

Description: This data collection contains readings of accumulation stake along the approximately 800 km long traverse route Neumayer-Kottas-Kohnen, Dronning Maud Land, Antarctica. By comparing the readings of an individual stake in two different seasons the amount of surface accumulation (i.e. snow deposition) or erosion (e.g. from sublimation of wind scour) can be determined. Stake readings were conducted approximately every year starting from season 1995/1996 to 2005/2006 as part of the European Project for Ice Coring In Antarctica (EPICA). The readings were carried out by a dedicated two to three person team accompanying the traverse from Neumayer station to Kohnen station. The readings were performed by a simple measurement of the visible length of the stake above the snow surface. For tilted stakes, the vertical height above the surface as well as the length of the stake was measured. New stakes were deployed when less than about 1.5 m of the previous stake was visible or a stake was lost (e.g. from breaking off or falling over and finally get burried in snow). Consequently, at some locations more than one stake is visible for several years (e.g. when the average snow accumulation was rather low). In those cases all visible stakes were recorded at the same location of such a stake cluster and added to the table as Height_1, Height 2, Height 3). Positions were measured with a simple GPS with coarse acquisition accuracy (order of several meters to tens of meters), which is sufficiently accurate to separate different stake locations (usually 500 m apart and horizontal displacement smaller than about 150 m/a, with largest displacements on the Ekström ice shelf). In very few cases, empty lines originate from missing stakes and the required position. In very few cases, a second line with the same coordinate corresponds to the same location with a fourth stake deployed as a new stake. From Neumayer station to Kottas camp stakes were deployed at approximately a 500 m interval. As the spatial variation of accumulation on the polar plateau is smaller than in the lower foreland (in this case the Ritscherflya) the stake distances was increased to 1 km to several kilometers from Kottas camp onto the polar plateau to Kohnen station. Additional field comments made by observing personal were removed from the files. However, original field notes in notebooks are available from AWI's Archive for German Polar Research (Oerter et al., 2013). Although surface accumulation is still one of the major unknowns to determine the the total surface mass balance of the Antarctic ice sheet, especially under climate change, direct long-term observations of surface accumulation are still one of the major gaps in field observations (Eisen et al., 2008). This time series of stake readings provides the basis for calculation the change in accumulation in space and time (e.g. Rotschky et al., 2007). It is thus fundamental for a decade-long record of the spatio-temporal characteristics of surface accumulation, which can be put into context to meteorological and oceanographic changes in the region.

Description: This data collection contains readings of accumulation stake along the approximately 800 km long traverse route Neumayer-Kottas-Kohnen, Dronning Maud Land, Antarctica. By comparing the readings of an individual stake in two different seasons the amount of surface accumulation (i.e. snow deposition) or erosion (e.g. from sublimation of wind scour) can be determined. Stake readings were conducted approximately every year starting from season 1995/1996 to 2005/2006 as part of the European Project for Ice Coring In Antarctica (EPICA). The readings were carried out by a dedicated two to three person team accompanying the traverse from Neumayer station to Kohnen station. The readings were performed by a simple measurement of the visible length of the stake above the snow surface. For tilted stakes, the vertical height above the surface as well as the length of the stake was measured. New stakes were deployed when less than about 1.5 m of the previous stake was visible or a stake was lost (e.g. from breaking off or falling over and finally get burried in snow). Consequently, at some locations more than one stake is visible for several years (e.g. when the average snow accumulation was rather low). In those cases all visible stakes were recorded at the same location of such a stake cluster and added to the table as Height_1, Height 2, Height 3). Positions were measured with a simple GPS with coarse acquisition accuracy (order of several meters to tens of meters), which is sufficiently accurate to separate different stake locations (usually 500 m apart and horizontal displacement smaller than about 150 m/a, with largest displacements on the Ekström ice shelf). In very few cases, empty lines originate from missing stakes and the required position. In very few cases, a second line with the same coordinate corresponds to the same location with a fourth stake deployed as a new stake. From Neumayer station to Kottas camp stakes were deployed at approximately a 500 m interval. As the spatial variation of accumulation on the polar plateau is smaller than in the lower foreland (in this case the Ritscherflya) the stake distances was increased to 1 km to several kilometers from Kottas camp onto the polar plateau to Kohnen station. Additional field comments made by observing personal were removed from the files. However, original field notes in notebooks are available from AWI's Archive for German Polar Research (Oerter et al., 2013). Although surface accumulation is still one of the major unknowns to determine the the total surface mass balance of the Antarctic ice sheet, especially under climate change, direct long-term observations of surface accumulation are still one of the major gaps in field observations (Eisen et al., 2008). This time series of stake readings provides the basis for calculation the change in accumulation in space and time (e.g. Rotschky et al., 2007). It is thus fundamental for a decade-long record of the spatio-temporal characteristics of surface accumulation, which can be put into context to meteorological and oceanographic changes in the region.

Description: This data collection contains readings of accumulation stake along the approximately 800 km long traverse route Neumayer-Kottas-Kohnen, Dronning Maud Land, Antarctica. By comparing the readings of an individual stake in two different seasons the amount of surface accumulation (i.e. snow deposition) or erosion (e.g. from sublimation of wind scour) can be determined. Stake readings were conducted approximately every year starting from season 1995/1996 to 2005/2006 as part of the European Project for Ice Coring In Antarctica (EPICA). The readings were carried out by a dedicated two to three person team accompanying the traverse from Neumayer station to Kohnen station. The readings were performed by a simple measurement of the visible length of the stake above the snow surface. For tilted stakes, the vertical height above the surface as well as the length of the stake was measured. New stakes were deployed when less than about 1.5 m of the previous stake was visible or a stake was lost (e.g. from breaking off or falling over and finally get burried in snow). Consequently, at some locations more than one stake is visible for several years (e.g. when the average snow accumulation was rather low). In those cases all visible stakes were recorded at the same location of such a stake cluster and added to the table as Height_1, Height 2, Height 3). Positions were measured with a simple GPS with coarse acquisition accuracy (order of several meters to tens of meters), which is sufficiently accurate to separate different stake locations (usually 500 m apart and horizontal displacement smaller than about 150 m/a, with largest displacements on the Ekström ice shelf). In very few cases, empty lines originate from missing stakes and the required position. In very few cases, a second line with the same coordinate corresponds to the same location with a fourth stake deployed as a new stake. From Neumayer station to Kottas camp stakes were deployed at approximately a 500 m interval. As the spatial variation of accumulation on the polar plateau is smaller than in the lower foreland (in this case the Ritscherflya) the stake distances was increased to 1 km to several kilometers from Kottas camp onto the polar plateau to Kohnen station. Additional field comments made by observing personal were removed from the files. However, original field notes in notebooks are available from AWI's Archive for German Polar Research (Oerter et al., 2013). Although surface accumulation is still one of the major unknowns to determine the the total surface mass balance of the Antarctic ice sheet, especially under climate change, direct long-term observations of surface accumulation are still one of the major gaps in field observations (Eisen et al., 2008). This time series of stake readings provides the basis for calculation the change in accumulation in space and time (e.g. Rotschky et al., 2007). It is thus fundamental for a decade-long record of the spatio-temporal characteristics of surface accumulation, which can be put into context to meteorological and oceanographic changes in the region.

Description: This data collection contains readings of accumulation stake along the approximately 800 km long traverse route Neumayer-Kottas-Kohnen, Dronning Maud Land, Antarctica. By comparing the readings of an individual stake in two different seasons the amount of surface accumulation (i.e. snow deposition) or erosion (e.g. from sublimation of wind scour) can be determined. Stake readings were conducted approximately every year starting from season 1995/1996 to 2005/2006 as part of the European Project for Ice Coring In Antarctica (EPICA). The readings were carried out by a dedicated two to three person team accompanying the traverse from Neumayer station to Kohnen station. The readings were performed by a simple measurement of the visible length of the stake above the snow surface. For tilted stakes, the vertical height above the surface as well as the length of the stake was measured. New stakes were deployed when less than about 1.5 m of the previous stake was visible or a stake was lost (e.g. from breaking off or falling over and finally get burried in snow). Consequently, at some locations more than one stake is visible for several years (e.g. when the average snow accumulation was rather low). In those cases all visible stakes were recorded at the same location of such a stake cluster and added to the table as Height_1, Height 2, Height 3). Positions were measured with a simple GPS with coarse acquisition accuracy (order of several meters to tens of meters), which is sufficiently accurate to separate different stake locations (usually 500 m apart and horizontal displacement smaller than about 150 m/a, with largest displacements on the Ekström ice shelf). In very few cases, empty lines originate from missing stakes and the required position. In very few cases, a second line with the same coordinate corresponds to the same location with a fourth stake deployed as a new stake. From Neumayer station to Kottas camp stakes were deployed at approximately a 500 m interval. As the spatial variation of accumulation on the polar plateau is smaller than in the lower foreland (in this case the Ritscherflya) the stake distances was increased to 1 km to several kilometers from Kottas camp onto the polar plateau to Kohnen station. Additional field comments made by observing personal were removed from the files. However, original field notes in notebooks are available from AWI's Archive for German Polar Research (Oerter et al., 2013). Although surface accumulation is still one of the major unknowns to determine the the total surface mass balance of the Antarctic ice sheet, especially under climate change, direct long-term observations of surface accumulation are still one of the major gaps in field observations (Eisen et al., 2008). This time series of stake readings provides the basis for calculation the change in accumulation in space and time (e.g. Rotschky et al., 2007). It is thus fundamental for a decade-long record of the spatio-temporal characteristics of surface accumulation, which can be put into context to meteorological and oceanographic changes in the region.

Description: This data collection contains readings of accumulation stake along the approximately 800 km long traverse route Neumayer-Kottas-Kohnen, Dronning Maud Land, Antarctica. By comparing the readings of an individual stake in two different seasons the amount of surface accumulation (i.e. snow deposition) or erosion (e.g. from sublimation of wind scour) can be determined. Stake readings were conducted approximately every year starting from season 1995/1996 to 2005/2006 as part of the European Project for Ice Coring In Antarctica (EPICA). The readings were carried out by a dedicated two to three person team accompanying the traverse from Neumayer station to Kohnen station. The readings were performed by a simple measurement of the visible length of the stake above the snow surface. For tilted stakes, the vertical height above the surface as well as the length of the stake was measured. New stakes were deployed when less than about 1.5 m of the previous stake was visible or a stake was lost (e.g. from breaking off or falling over and finally get burried in snow). Consequently, at some locations more than one stake is visible for several years (e.g. when the average snow accumulation was rather low). In those cases all visible stakes were recorded at the same location of such a stake cluster and added to the table as Height_1, Height 2, Height 3). Positions were measured with a simple GPS with coarse acquisition accuracy (order of several meters to tens of meters), which is sufficiently accurate to separate different stake locations (usually 500 m apart and horizontal displacement smaller than about 150 m/a, with largest displacements on the Ekström ice shelf). In very few cases, empty lines originate from missing stakes and the required position. In very few cases, a second line with the same coordinate corresponds to the same location with a fourth stake deployed as a new stake. From Neumayer station to Kottas camp stakes were deployed at approximately a 500 m interval. As the spatial variation of accumulation on the polar plateau is smaller than in the lower foreland (in this case the Ritscherflya) the stake distances was increased to 1 km to several kilometers from Kottas camp onto the polar plateau to Kohnen station. Additional field comments made by observing personal were removed from the files. However, original field notes in notebooks are available from AWI's Archive for German Polar Research (Oerter et al., 2013). Although surface accumulation is still one of the major unknowns to determine the the total surface mass balance of the Antarctic ice sheet, especially under climate change, direct long-term observations of surface accumulation are still one of the major gaps in field observations (Eisen et al., 2008). This time series of stake readings provides the basis for calculation the change in accumulation in space and time (e.g. Rotschky et al., 2007). It is thus fundamental for a decade-long record of the spatio-temporal characteristics of surface accumulation, which can be put into context to meteorological and oceanographic changes in the region.

Description: This data collection contains readings of accumulation stake along the approximately 800 km long traverse route Neumayer-Kottas-Kohnen, Dronning Maud Land, Antarctica. By comparing the readings of an individual stake in two different seasons the amount of surface accumulation (i.e. snow deposition) or erosion (e.g. from sublimation of wind scour) can be determined. Stake readings were conducted approximately every year starting from season 1995/1996 to 2005/2006 as part of the European Project for Ice Coring In Antarctica (EPICA). The readings were carried out by a dedicated two to three person team accompanying the traverse from Neumayer station to Kohnen station. The readings were performed by a simple measurement of the visible length of the stake above the snow surface. For tilted stakes, the vertical height above the surface as well as the length of the stake was measured. New stakes were deployed when less than about 1.5 m of the previous stake was visible or a stake was lost (e.g. from breaking off or falling over and finally get burried in snow). Consequently, at some locations more than one stake is visible for several years (e.g. when the average snow accumulation was rather low). In those cases all visible stakes were recorded at the same location of such a stake cluster and added to the table as Height_1, Height 2, Height 3). Positions were measured with a simple GPS with coarse acquisition accuracy (order of several meters to tens of meters), which is sufficiently accurate to separate different stake locations (usually 500 m apart and horizontal displacement smaller than about 150 m/a, with largest displacements on the Ekström ice shelf). In very few cases, empty lines originate from missing stakes and the required position. In very few cases, a second line with the same coordinate corresponds to the same location with a fourth stake deployed as a new stake. From Neumayer station to Kottas camp stakes were deployed at approximately a 500 m interval. As the spatial variation of accumulation on the polar plateau is smaller than in the lower foreland (in this case the Ritscherflya) the stake distances was increased to 1 km to several kilometers from Kottas camp onto the polar plateau to Kohnen station. Additional field comments made by observing personal were removed from the files. However, original field notes in notebooks are available from AWI's Archive for German Polar Research (Oerter et al., 2013). Although surface accumulation is still one of the major unknowns to determine the the total surface mass balance of the Antarctic ice sheet, especially under climate change, direct long-term observations of surface accumulation are still one of the major gaps in field observations (Eisen et al., 2008). This time series of stake readings provides the basis for calculation the change in accumulation in space and time (e.g. Rotschky et al., 2007). It is thus fundamental for a decade-long record of the spatio-temporal characteristics of surface accumulation, which can be put into context to meteorological and oceanographic changes in the region.