In the ongoing discussion about climate change, the climate of the polar regions is one of the foci of attention. Whereas the enhanced warming that models predict for the polar regions is obvious in the Arctic , Antarctica behaves differently. Not only an increase in sea ice extent is observed but also the expected warming combined with a corresponding increase in precipitation and thus increased surface mass balance is still not observed over the entire Antarctic continent.

Only the wider Antarctic Peninsula region (including parts of West Antarctica) exhibits a large increase in air temperature , accompanied by disintegrating ice shelves and accelerated ice flow . For East Antarctica, no general warming and increase in precipitation is found in surface observational data . This is important because an increase in precipitation, and hence increased surface mass balance (SMB), might mitigate sea level rise.

Close monitoring of changes in both the atmosphere and the cryosphere is necessary in order to detect early signs of climatic change in East Antarctica. In particular, the coastal regions are highly sensitive to any changes, since the temperatures are close to the melting point in summer already in the present climate .

Instrumental surface air temperature records from the Antarctic continent are available only since the International Geophysical Year (IGY) 1957–1958. The number of stations is still limited and most of them are situated at the coast. Thus, to investigate the past climate, we have to rely on firn and ice cores. Temperature information is derived mainly from the stable water isotope ratio; annual mean SMB can be calculated from density measurements for cores where annual layers are resolved.

In Dronning Maud Land (DML), East Antarctica (Fig. ), various expeditions have carried out glaciological field work, including drilling of firn and ice cores in the past decades in the frame of different national and international programmes. In particular, the pre-site-survey expeditions connected to the European Project for Ice Coring in Antarctica (EPICA) have increased our knowledge about the hitherto poorly explored DML. Almost 80 cores have been drilled during these expeditions since 1980. However, so far only the results of single expeditions have been published; no comprehensive study of this unique data set had been carried out. In this study, the spatial and temporal variations of stable isotope ratios and SMB derived from a network of 76 cores were investigated. Calculation of stacked records helped to considerably improve the signal-to-noise ratio. The spatial variations were related to topographic and other geographical features. Possible climatic trends in SMB and δ18O were investigated. Additionally, the relationship between δ18O and SMB and possible influences of the Southern Annular Mode (SAM) as the primary mode of atmospheric variability in the extratropical Southern Hemisphere were analysed.

Dronning Maud Land is situated in East Antarctica approximately between 20∘ W and 45∘ E. It covers an area of ca. 2700 000 km2. Our study is focused on the western part of DML, between 15∘ W and 10∘ E (see Fig. ). DML is bounded by various ice shelves of different sizes. The westernmost ice shelf, for which cores are available for this investigation, is the Riiser-Larsen Ice Shelf with a width of about 400 km. Further east, the Ekström Ice Shelf is found, which is bounded by two N–S stretching ridges, Søråsen and Halvfarryggen. Centred at the Greenwich meridian is the Fimbul Ice Shelf, with an area of 33 000 m2 one of the largest ice shelves in DML. It extends approximately 100 km in N–S direction and 200 km in E–W direction and is fed by Jutulstraumen, the largest outlet glacier in DML. The lower inland region Ritscherflya is situated south of the Riiser-Larsen and Ekström ice shelves. A mountain range to the southeast, Heimefrontfjella, separates Ritscherflya from the higher plateau area, the so-called Amundsenisen.

Early glaciological measurements were carried out in our study area by the British–Swedish–Norwegian Expedition 1949–1952 . Thereafter, DML was only visited sporadically until the early 1980s. Systematic data acquisition began in the 1980s on the Ekström Ice Shelf, connected to the German year-round scientific base Georg-von-Neumayer. Various traverses started at this station since 1986/1987 . Glaciological field work was performed along the traverse routes from the Ekström Ice Shelf to Heimefrontfjella and, in the frame of EPICA, to Amundsenisen.

More recently, several shallow firn cores were retrieved at Søråsen and Halvfarryggen . However, these cores are strongly influenced by local topography and are therefore not directly comparable to the other cores. (For the sake of completeness we did not omit them from our study.)

The lower inland region Ritscherflya was visited during the field season 1988/1989 as part of the Swedish Antarctic Research Programme (SWEDARP). The SMB and δ18O records generally showed large spatial and temporal variability .

As part of the Norwegian Antarctic Research Expedition (NARE), Norwegian groups investigated the spatial and temporal variability of SMB on a traverse that crossed the Fimbul Ice Shelf (e.g. and ). In austral summer 2000/2001, a 100 m deep ice core was retrieved on the eastern Fimbul Ice Shelf. The derived accumulation rates showed high temporal variability and a significant negative trend in the 20th century .

used eight firn cores from coastal DML to study the long-term changes in accumulation and δ18O in the area and the role of the Southern Annular Mode (SAM) and ENSO (El Niño–Southern Oscillation) in the temporal variability of δ18O. The study revealed the diverging multidecadal trends in accumulation (decreasing) and δ18O (increasing) in coastal DML. On shorter sub-decadal time scales, it was found that the teleconnection of ENSO to the area is stronger in years when the SAM is in its negative phase.

In austral summers 2009–2011, eight shallow firn cores were retrieved on the Fimbul Ice Shelf during an extensive glaciological field campaign as part of the project “Fimbul Ice Shelf from top to bottom” that combined glaciological measurements with oceanographic measurements and modelling (http://fimbul.npolar.no). The δ18O exhibited a small positive trend, whereas a negative trend was observed in SMB during the last 30 years .

The majority of the extensive EPICA pre-site-survey programme was conducted on the high plateau region Amundsenisen. Between 1996 and 1998, a series of shallow firn cores and three medium-deep ice cores (see Appendix Table ) were drilled on Amundsenisen. The area was found to be characterized by a robust deposition system with nearly constant accumulation rates for the last millennium . calculated a mean value of 57±15 kgm-2a-1, with higher values in the western part of Amundsenisen.

used a special interpolation method to derive a surface accumulation map for western DML from firn cores, snow pits, and stake measurements. The accumulation was found to clearly decrease with elevation and distance from the coast, with local maxima and minima on the windward and lee sides of topographic ridges. This was confirmed by who compared Rotschky's results with data from a mesoscale atmospheric model.

presented data from the Norwegian US Scientific Traverse of East Antarctica TASTE-IDEA, through DML from the Norwegian base Troll to the South Pole, during which some earlier Norwegian drilling sites were revisited. The mean accumulation rate at Sites I and M (, see also Fig. ) has not changed since the earlier measurements. investigated the spatial and temporal variability of accumulation in DML using snow pits, firn cores and radar data from an IPY traverse between Kohnen Station and Dome Fuji (along ID2, Fig. 1 and further east). They found a positive trend in accumulation for central DML in the past 50 years. provided a synthesis of Antarctic SMB during the last 800 years. They stated that SMB over most of Antarctica does not exhibit an overall clear trend. However, they found a clear increase in SMB in coastal regions and over the highest part of the East Antarctic ice divide since the 1960s, which confirms the results of but contradicts those of and . used volcanic time markers to investigate century-scale SMB changes in ice cores retrieved during the above-mentioned traverse from Troll to South Pole but found that almost all sites above 3200 m altitude show a decrease in SMB in the last 50 years.

76 shallow firn cores from DML were analysed in order to assess the spatial and temporal variability of water stable isotope ratios (δ18O) and SMB. This was the first comprehensive study of this data set from coastal, transitional and interior DML. The large number of cores reduced depositional noise and enhanced the signal-to-noise variance ratio considerably compared to earlier investigations of subsets of the firn core data. Thus possible climatic trends could be analysed with a higher reliability than previously.

The temporal variations of δ18O and SMB derived from the plateau cores are distinctly different from those of the coastal cores. The SMB on the inland plateau is positively correlated to the stable isotope ratio; thus it seems to be mainly affected by temperature-dependent, thermodynamic influences, namely the saturation vapour pressure. Higher temperatures mean higher saturation vapour pressure, thus more moisture and potentially larger amounts of precipitation. On the contrary, the SMB of the coastal cores does not change in accordance with the changes in δ18O. Precipitation and thus SMB in the coastal areas are dependent on the synoptic activity in the circumpolar trough. Usually precipitation is connected to frontal systems of cyclones moving from west to east north of the coast. Changes in the synoptic activity in and north of the circumpolar trough can have a strong impact on precipitation seasonality as well as precipitation amounts, depending on the strength and location of the trough and the type of the atmospheric circulation (zonal/meridional flow) .

Precipitation at the plateau occurs in form of diamond dust on most days of the year. It consists of very fine ice crystals that form due to radiative cooling in almost saturated air. However, it was found that also real snowfall is observed in the interior of the continent. It is connected to advection of warm air due to amplification of Rossby waves and consequent orographic lifting of the air mass. These snowfall events, even though they are rare, can bring up to 50% of the annual accumulation . Therefore the dynamic influence on stable water isotope ratios and SMB is not restricted to the coastal areas and should be discussed generally. For instance, a considerably lower ratio of winter/summer accumulation during a colder period could lead to higher annual mean δ18O values in the firn core because the contribution of the colder season to the annual mean would be comparatively small. Thus a change in precipitation (and hence accumulation) seasonality could lead to a positive or negative bias in the temperatures derived from δ18O of an ice/firn core, depending on which seasons were preferred .

For the broad relative maximum of δ18O in the second half of the 19th century, the corresponding SMB is still generally lower than the average. This would mean that winter accumulation would have decreased even stronger than summer accumulation. A combination of the thermodynamic effect (generally lower SMB due to lower temperature) and dynamic effects (less precipitation events in winter due to e.g. a more zonal flow or more northern location of the sea ice edge and thus of the frontal zone) could explain the observed features. Recent data alone are not sufficient to confirm this hypothesis. More detailed investigations combined with modelling studies are necessary to shed more light on this problem.

The lack of correlation between SAM index, air temperature and δ18O for the ice shelf regions is highly interesting. The reasons are not yet entirely clear. Variations in SMB and its seasonality certainly play an important role here. Stronger westerlies and more intense cyclone activity do not necessarily have to lead to higher accumulation. The coastal areas are always influenced by the synoptic activity in the circumpolar trough. Higher wind speeds and faster moving cyclones alone could lead to less accumulation due to reduced duration of precipitation events. Apart from that, a more zonal flow and less meridional exchange of heat and moisture would mean that precipitation amounts for single events were smaller than in a period with negative SAM index. Thus even a higher number of precipitation events would not necessarily lead to a higher SMB. Therefore low SMB values could be due to both dynamic and thermodynamic influences.

For δ18O, a positive SAM means a generally more local moisture source, thus less isotopic fractionation and higher δ18O values than in a period with negative SAM index, even though the temperature might have been relatively low.

Another important factor that influences the stable isotope ratio of Antarctic precipitation is sea ice. It determines the availability of water vapour and has a strong influence on the energy balance of the ocean, thus changing temperature and moisture amounts in the air above the water/ice surface . However, in the DML region sea ice does not show any systematic differences in relation to SAM (e.g. ); thus the influence of sea ice on the ice core properties cannot be discussed on the given time scale for the presented data set.

Apart from all factors that affect precipitation, it should be kept in mind that also post-depositional processes alter the stable isotope ratio of the snow. Additional to the afore-mentioned redistribution of snow due to wind influence, the sublimation-deposition cycle can change the δ18O values. Diffusion in the pore space due to temperature gradients tends to smooth the seasonal variations . Most recent studies have shown that the interaction of the air in the pore space with the atmospheric layer just above the snow surface is more important than previously thought.

We conclude that, in the last 2 centuries, conditions in the interior DML have been fairly stable and only weakly influenced by changes in atmospheric dynamics. In the coastal areas, more complex processes are at work and the δ18O and SMB derived from the firn cores cannot be fully explained yet. In order to understand the temporal variability of δ18O, a full understanding of the three-dimensional moisture transport to Antarctica is required. Additionally to firn cores and snow samples, continuous monitoring of the stable isotope ratio of water vapour combined with high-resolution atmospheric modelling would be desirable.