Description: At the German wintering base Neumayer, an intensive glacio-meteorological program was carried out during the last two decades. A complete meteorological data set and data from surface snow samples, snow pits, firn cores, and weekly accumulation measurements from a stake array are available. We first investigated the attenuation of the seasonal d18O signal due to water vapour diffusion in the snow pack. A comparison of surface snow samples and firn cores of different age shows that only one third of the seasonal d18O signal of the surface snow samples remains in the cores after the first year. No further significant change in the amplitude of the seasonal d18O signal is found later. Changes in the seasonal distribution of accumulation can lead to a bias in ice core properties. This is studied on a short time scale, using the available high-time resolution data of accumulation, stable isotope ratios, and air temperature. Mean annual d18O values from firn cores are not well correlated to annual mean air temperatures. However, the correlation is improved considerably by weighting the annual mean air temperature by accumulation. At Neumayer, mainly the cyclonic activity in late winter/early spring determines whether and how the core data are biased.

Description: Old ice for paleoenvironmental studies retrieved by deep core drilling in the central regions of the big ice sheets can also be retrieved from the ice-sheet margins. The d18O-content of the surface ice was studied at 15 different Greenland ice-margin locations. At some locations, two or more records were obtained along closely spaced parallel sampling profiles, showing good reproducibility of the records. We present ice-margin d18O- records reaching back into the Pleistocene. Many of the characteristic d18O-variations known from Greenland deep ice-cores can be recognized, allowing an approximate time scale to be established along the ice-margin records. A flow line model is used to determine the location on the ice sheet where the margin-ice was originally deposited as snow. The Pleistocene-Holocene d18O-change at the deposition sites is determined by comparing the d18O-values in the ice-margin record to the present _18O-values of the surface snow at the deposition sites. On the northern slope of the Greenland ice sheet, the Pleistocene-Holocene d18O-change is c. 10 per mil in contrast to a change of 6-7 per mil at locations near the central ice divide. This is in accordance with deep ice-core results.We conclude that d18O-records measured on ice from the Greenland ice-sheet margin provide useful information about past climate and dynamics of the ice sheet, and thus are important (and cheap) supplements to deep ice core records.

Description: Grain size is an important but not well known characteristics of snow at the surface of Antarctica. In the past, grain size has been reported using various methods, the reliability, reproducibility and inter comparability of which is not warranted. In this paper, we present and recommend, depending on available logistical support, 3 techniques of snow grain sampling and /or imaging in the field as well as an ariginal digital image processing method, which we have proved to provide reproducible and intercomparable measures of a snow grain size parameter, the mean convex radius. Results from more than 500 samples and 3000 images of snow grains presented, which yield a still spatially limited, yet unprecendtedly wide picture of near-surface snow grain size distribution from field work in Antarctica. In particular, except at sites affected by a very particular meteorology, surface grains in the interior of the ice sheet are uniformly small (o.1 to 0.2 mm). The climate-related increase of grain size with depth through metamorphism is, as expected, not spatially uniform. Our Antarctic snow grain size database will continue to grow as field investigators bring new samples, images and measures of snow grain size.

Description: We have investigated the fracture of Antarctic shelf ice core using two fracture mechanics test methods: the chevron-notched short-rod specimen loaded in tension and the chevron-notched round-bar specimen loaded in three-point bending. These tests have been used to measure the fracture initiation toughness, K init, at which crack growth starts, on samples taken through the entire thickness of the Ronne Ice Shelf, from low-density firn through consolidated meteoric ice to basal marine ice. The fracture data are presented together with depth profiles of relevant physical and mechanical properties derived from the test specimens: temperature, density, elastic modulus, and grain size. It is found that the trend in measured fracture toughness closely reflects changes in ice density and elastic modulus. We augment the experiment study by presenting a fracture mechanics analysis of ice shelf surface and basal crevassing which directly incorporates our measurements. For the examined ice shelf profiles, basal crevasses are found to be inherently unstable unless an external restraining force is imposed, which has important implications for overall ice shelf stability. On the other hand, surface crevassing is shown to be innately stable at depth. Our fracture mechanics model is used to predict local ice shelf back stress in the vicinity of basal crevassing and is validated directly against field observations of crevasse penetration on the Ronne Ice Shelf.

Description: The accumulation rate is one important glaciological parameter influencing growth and movement of an ice sheet. It is also needed for the interpretation of physical and chemical properties measured at ice cores. Accumulation rates show a wide spatial and temporal variability. For Dronning Maud Land (DML) an attempt was made to collect the available accumulation data and compile a map of the distribution of accumulation rates. The data at 122 locations are based on snow pit studies (covering at least 5 years) and firn cores covering from decades up to 200 years of accumulation. The oldest data had been collected during the Norwegian-British-Swedish Expedition 1949-52. However, the major part of the data were collected during the EPICA pre-site survey in DML, carried out by Alfred-Wegener Institute for Polar and Marine Research, Germany, British Antarctic Survey, the Norwegian Antarctic Research Expeditions and the Swedish Antarctic Research Programme in co-operation with Utrecht University. In addition, also the data of the US South Pole Queen Maud Land Traverse 1965-68 were included. To judge the temporal variability of the accumulation rates the data for various periods are compared with a 200-years time series of accumulation rates for the interior part of the ice sheet, calculated from 20 firn cores. For compiling the map the ArcGis 8.1 software was used. After testing several interpolation algorithms the inverse distance weighted method (IDW) was chosen. The data are interpolated with 5 km x 5 km resolution, using 20 neighbouring points. A very characteristic feature in DML are the mountain ranges from Maudheimvidda in the West to Wohlthat-Massiv in the East which separate the interior high part of the ice sheet and the lower parts, e.g. Ritscherflya, extending towards the ice shelves. To account for this barrier two domains were introduced, separated approximately by the 2000 m contour line. The plotted isolines have a distance of 50 kg m-2 a-1, the steps of 10 kg m-2 a-1 are indicated by a colour code. The map shows clearly the general trend of decreasing accumulation rates from the coastal area to the interior of the ice sheet. However, recognizable is a certain patchiness with high accumulation, e.g. on Jutulstraumen, and low accumulation areas, obviously due to wind erosion. For one selected profile line the map data and accumulation data from multi-year stake readings are compared.

Description: In the framework of the European Project for Ice Coring in Antarctica (EPICA) a glacio-chemical pre-sitesurvey was carried out in Dronning Maud Land (DML), Antarctica. Up to now three intermediate deep icecores and twelve snow pits have been analysed by ion chromatography. The spatial and seasonal variationsof the snow chemistry in DML, covering the time period 1997 to 1865, are presented. Summer maxima insulphate and winter maxima in sea-salt components are well archived in the area under investigation,while for nitrate and methanesulphonic acid (MSA) seasonal variations could not be unambiguouslydetected due to postdepositional changes. Average concentrations of sea-salt components and nitrateare spatially uniform in the plateau region, however sea salt shows an exponential decline with altitudefor elevations below 2800 m a.s.l. Non-seasalt sulphate shows a 40% increase with lower snowaccumulation, while MSA shows a 50% decline with higher elevation and lower accumulation. The outcomeof this study supports that the data of the new EPICA deep drilling site in DML (0°04.07' E, 75°00.10' S)will be geographical representative for this region. High-resolution analytical methods will allow accuratestratigraphic dating of the core, at least for the Holocene period.