Two medium-depth ice cores were retrieved from Berkner Island by a joint project between the Alfred-Wegener-Institut and the British Antarctic Survey in the 1994/95 field season. A 151 in deep core from the northern dome (Reinwarthhohe) of Berkner Island spans 700 years, while a 181 in deep core from the southern dome (Thyssenhohe) spans approximately 1200 years. Both cores display clear seasonal cycles in electrical conductivity measurements, allowing dating by annual-layer counting and the calculation of accumulation profiles. Stable-isotope measurements (both delta(18)O and deltaD), together with the accumulation data, allow us to estimate changes in climate for most of the past millennium: the data show multi-decadal variability around a generally stable long-term mean. In addition, a full suite of major chemistry measurements is available to define the history of aerosol deposition at these sites: again, there is little evidence that the chemistry of the sites has changed over the past six centuries. Finally, we suggest that the southern dome, with an ice thickness of 950 in, is an ideal site from which to gain a climate history of the late stages of the last glacial and the deglaciation for comparison with the records from the deep Antarctic ice cores, and with other intermediate-depth cores such as Taylor Dome and Siple Dome.

The European Project for Ice Coring in Antarctica (EPICA) includes a comprehensive pre-site survey on the inland ice plateau of Dronning Maud Land. This paper focuses on the investigation of the O-18 content of shallow firn and ice cores. These cores were dated by profiles derived from dielectric-profiling and continuous flow analysis measurements. The individual records were stacked in order to obtain composite chronologies of O-18 contents and accumulation rates with enhanced signal-to-noise variance ratios. These chronologies document variations in the last 200 and 1000 years. The O-18 contents and accumulation rates decreased in the 19th century and increased during the 20th century. Using the empirical relationships between stable isotopes, accumulation rates and the 10 in firn temperature, the variation of both parameters can be explained by the same temperature history. But other causes for these variations, such as the build-up of the snow cover, cannot be excluded. A marked feature of the 1000 year chronology occurs during the period AD 1180-1530 when the O-18 contents remains below the long-term mean. Cross-correlation analyses between five cores from the Weddell Sea region and Dronning Maud Land show that O-18 records can in some periods be positively correlated and in others negatively correlated, indicating a complex climatic history in time and space.

The chemical stratigraphy of the surface firn of the central Filchner- Ronne Ice Shelf was determined in conjunction with stable isotopes from shallow firn cores and snow-pit samples collected at 1.1 widely distributed sites, and covering a time period of at least 20 years. The chemical analysis included ECM profiling and the determination of chloride, non-sea-salt (nss) sulphate, methanesulphonate (MSA), nitrate and, partly, sodium and bromide. Throughout the investigated area, winter time nss sulphate levels are found to be substantially negative, indicating that the sulphate to sodium ratio in airborne sea-salt particles is depleted by a factor of 5, approximately, in relation to the bulk sea-water ratio. While winter firn layers appear to be marked by episodic events of large sea-salt inputs, pronounced annual cycles with maxima in summer firn layers are commonly observed for the ECM signal and for nss sulphate, nitrate and MSA at all sites. For MSA, however, this phase relation is almost reversed for depths greater than 3-4m.The mean impurity levels consistently are strongly depleted with increasing distance from the ice edge by about 30% / 100 km for sea salt, 25% / 100 km for MSA and only 10%/ 100 km for nss sulphate. However, no substantial trend is observed for nitrate. It is concluded, therefore, that the sea-salt and the biogenic sulphur compounds deposited on the Filchner-Ronne Ice Shelf mainly originate from the adjacent Weddell Sea.Further important implications of the continental effects are: (a) an atmospheric residence time of nss sulphate apparently exceeding that of MSA probably due to the supplementary sulphate production on the ice shelf from biogenic SO2, and (b) a substantial limitation of the potential of deep ice cores already drilled on the Filchner- Ronne Ice Shelf in extracting reliable net temporal changes of sea-salt and biogenic sulphur species.

The ice cap on Berkner Island is grounded on bedrock within the Filchner-Ronne Ice Shelf and is, therefore, expected to be a well-suited place to retrieve long-term ice-core records reflecting the environmental situation of the Weddell Sea region. Shallow firn cores were drilled to 11 m at the two main summits of Berkner Island and analysed in high depth resolution for electrical d.c. conductivity(ECM), stable isotopes, chloride, sulphate, nitrate and methane-sulphonate (MSA).From the annual layering of δD and non-sea-salt (nss) sulphate, a mean annual snow accumulation of 26.6 cm water at the north dome and 17.4cm water at the south domeare obtained. As a result of ineffective wind scouring indicated by a relatively lownear-surface snow density, regular annual cycles are found for all species at least in the upper 4-5 m. Post-depositional changes are responsible for a substantial decrease o[the seasonal δD and nitrate amplitude as well as for considerable migration of the MSA signal operating below a depth of 3-4 m. The mean chemical and isotopic firn properties at the south dome correspond to the situation on the Filchner-Ronne Ice Shelf at a comparable distance to the coast, whereas the north dome is found to be much more influenced by maritime air masses. Persistent high sea-salt levels in winter snow at Berkner Island heavily obscure the determination of nss sulphate probably due to sulphate fractionation in the Antarctic sea-salt aerosol. Estimated time-scale spredict ages at 400 m depth to be ~2000 years for the north and ~3000 years for the south dome. Pleistocene ice is expected in the bottom 200 and 300 m, respectively.

THE Filchner–Ronne ice shelf, which drains most of the marine-based portions of the West Antarctic ice sheet, is the largest ice shelf on Earth by volume. The origin and properties of the ice that constitutes this shelf are poorly understood, because a strong reflecting interface within the ice and the diffuse nature of the ice–ocean interface make seismic and radio echo sounding data difficult to interpret1,2. Ice in the upper part of the shelf is of meteoric origin, but it has been proposed2,5 that a basal layer of saline ice accumulates from below. Here we present the results of an analysis of the physical and chemical characteristics of an ice core drilled almost to the bottom of the Ronne ice shelf. We observe a change in ice properties at about 150 m depth, which we ascribe to a change from meteoric ice to basal marine ice. The basal ice is very different from sea ice formed at the ocean surface and we propose a formation mechanism in which ice platelets in the water column accrete to the bottom of the ice shelf.

A comparison of samples from a translucent green iceberg with a core from the Ronne Ice Shelf revealed an excellent agreement in isotopic composition, crystal structure, and incorporated sediment particles. Marine shelf ice which constitutes the basal portion of some ice shelves is considered to be the source of green icebergs. It most likely results from “ice pump” processes which produce large amounts of ice platelets in the water column beneath ice shelves. These subsequently accumulate and become compacted into bubble‐free, desalinated ice. Iceberg and drift‐buoy trajectories indicate that green icebergs observed in the Weddell Sea originate from the Amery Ice Shelf rather than from the Ronne Ice Shelf, although this ice shelf is also a potential source.