Abstract.It has been shown that NOs is produced photochemically within the snowpack of polar regions. If emitted to the atmosphere, this process could be a major source of NOs in remote snowcovered regions. We report here on measurements made at the German Antarctic station, Neumayer, during austral summer 1999, aimed at detecting and quantifying emissions of NO• from the surface snow. Gradients of NOs were measured, and fluxes calculated using local meteorology measurements. On the 2 days of flux measurements, the derived fluxes showed continual release from the snow surface, varying between ~0 and 3x108 molecs/cm2/s. When not subject to turbulence, the variation was coincident with the uv diurnal cycle, suggesting rapid release once photochemically produced. Scaling the diurnal average of Feb. 7th(1.3x108 molecs/cm2/s) suggests an annual emission over Antarctica of the order 0.0076TgN.

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ABSTRACT. The European Programme for Ice Coring in Antarctica includes a comprehensive pre-site survey on the inland ice plateau of Dronning Maud Land, Antarctica. The German glaciological programme during the 1997/98 field season was carried out along a 1200 km traverse on Amundsenisen and involved sampling the snow cover in pits and by shallow firn cores. This paper focuses on the accumulation studies.

Abstract. The ESA satellite CryoSat-2 has been observing Earth's polar regions since April 2010. It carries a sophisticated radar altimeter and aims for the detection of changes in sea ice thickness as well as surface elevation changes of Earth's land and marine ice sheets. This study focuses on the Greenland and Antarctic ice sheets, considering the contemporary elevation of their surfaces. Based on 2 years of CryoSat-2 data acquisition, elevation change maps and mass balance estimates are presented. Additionally, new digital elevation models (DEMs) and the corresponding error maps are derived. Due to the high orbit of CryoSat-2 (88° N/S) and the narrow across-track spacing, more than 99% of Antarctica's surface area is covered. In contrast, previous radar altimeter measurements of ERS1/2 and ENVISAT were limited to latitudes between 81.5° N and 81.5° S and to surface slopes below 1°. The derived DEMs for Greenland and Antarctica have an accuracy which is similar to previous DEMs obtained by satellite-based laser and radar altimetry (Liu et al., 2001; Bamber et al., 2009, 2013; Fretwell et al., 2013; Howat et al., 2014). Comparisons with ICESat data show that 80% of the CryoSat-2 DEMs have an error of less than 3 m ± 30 m. For both ice sheets the surface elevation change rates between 2011 and 2012 are presented at a resolution of 1 km. Negative elevation changes are concentrated at the west and south-east coast of Greenland and in the Amundsen Sea embayment in West Antarctica (e.g. Pine Island and Thwaites glaciers). They agree well with the dynamic mass loss observed by ICESat between 2003 and 2008 (Pritchard et al., 2009). Thickening occurs along the main trunk of Kamb Ice Stream and in Dronning Maud Land. While the former is a consequence of an ice stream stagnated ∼150 years ago (Rose, 1979; Retzlaff and Bentley, 1993), the latter represents a known large-scale accumulation event (Lenaerts et al., 2013). This anomaly partly compensates for the observed increased volume loss in West Antarctica. In Greenland the findings reveal an increased volume loss of a factor of 2 compared to the period 2003 to 2008. The combined volume loss of Greenland and Antarctica for the period 2011 and 2012 is estimated to be −448 ± 122 km3 yr−1.

A 181 m long ice core was drilled at 79°36’51"S, 45°43’28" W, near the summit of Berkner Island, Antarctica (886 m a.s.L). Berkner Island is located between the Filchner and Ronne Ice Shelves, and the ice near the summit shows little lateral flow. The density of the ice core was measured every 3 mm along its length, using attenuation of a gamma-ray beam, which gave an absolute accuracy of 2%. As expected, there is a general density increase with depth, the maximum densities of > 900 kg m−3 being reached just above 100 m depth. Comparison with the electrical conductivity method (ECM) shows density variations with the same wavelength as the annual signals, which can be seen in the ECM log (higher acidity during summer). In the shallowest part of the core, the density of winter layers is higher than that of summer layers, a relationship which is reversed at greater depth. We assume that the densification rates for the two types of firn are different. Similar density phenomena were observed on ice cores from Greenland, showing that such phenomena are not a local effect.

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By analyzing the records in the frequency domain, no persistent periods were found. This suggests that the snow accumulation in this area is mainly influenced by local deposition patterns and may be additionally masked by redistribution of snow due to wind. By comparing accumulation rates over the last 2 millennia a distinct change in the layer thickness in one of the three cores was found, which might be attributed either to an area upstream of the drilling site with lower accumulation rates, or to deposition processes influenced by surface undulations. The missing of a clear correlation between the accumulation rate histories at the three locations is also important for the interpretation of small, short time variations of past precipitation records obtained from deep ice cores.

The accumulation defined as ''precipitation minus evaporation'' over Greenland has been simulated with the high-resolution limited-area regional climate model HIRHAM4 applied over an Arctic integration domain. This simulation is compared with a revised estimate of annual accumulation rate distribution over Greenland taking into account information from a new set of ice core analyses, based on surface sample collections from the North Greenland Traverse. The region with accumulation rates below 150 mm yr Ϫ1 in central-northwest Greenland is much larger than previously assumed and extends about 500 km farther to the south. It is demonstrated that good agreement between modeled and observed regional precipitation and accumulation patterns exists, particularly concerning the location and the values of very low accumulation in the middle of Greenland. The accumulation rates in the northern part of Greenland are reduced in comparison to previous estimates. These minima are connected with a prevailing blocking high over the Greenland ice sheet and katabatic wind systems preventing humidity transports to central Greenland. The model reasonably represents the synoptic situations that lead to precipitation. Maxima of precipitation and accumulation occur at the southwestern and southeastern coasts of Greenland and are connected with cyclonic activity and the main storm tracks around Greenland. The central region of the Greenland ice sheet acts as a blocking barrier on moving weather systems and prohibits cyclones moving from west to east across this region and, thus prevents moisture transports.