DML Precipitation regime and EPICA ice core interpretation

To assess the present or future possible climate changes a thorough understanding of the climate of the past is required. Valuable information about former climates comes from ice cores drilled into the large ice sheets of Greenland and Antarctica. We expect considerable new knowledge from two cores drilled in the frame of the European Project for Ice Coring in Antarctica, (EPICA) at Dome C and at Kohnen Station, Dronning Maud Land (DML), respectively. However, for a correct interpretation of the ice core data we need to understand the meteorological processes that are responsible for the precipitation sampled in the cores. The DML core is of special interest, because of all deep drillings from the interior of the continent it is the one closest to the coast and most influenced by synoptic processes in the polar ocean due to the proximity to the Antarctic Peninsula. The Peninsula represents a barrier for the prevailing westerly winds and thus frequently causes cyglogenesis on its lee side. During the EPICA pre-site survey expeditions a considerable number of shallow firn cores (10m-160m depth) have been drilled by German (45 cores), Scandinavian (14 cores), and British (6 cores) scientists covering time periods between 2000 and 50 years. Most of these cores have been investigated and interpreted in terms of climate already, divided into groups defined by expedition year, nationality etc. However, no comprehensive study of this unique data set from all available cores of DML has ever been carried out. The proposed study starts with an investigation of the DML precipitation regime using an archive of numerical weather model forecasts from the AMPS (Antarctic Mesoscale Prediction System), which has been run by the National Center for Atmospheric Research (NCAR), Boulder, CO since September 2000. AMPS employs the Polar MM5 (5 th generation Mesoscale Model of Pennsylvania State University-NCAR, optimized for use over ice sheets) and was adapted especially for storm and precipitation forecasting purposes with the active feedback of the aviation forecasters at McMurdo Station, Antarctica. It is the only available high-resolution circumpolar model and is nested within the global model from NCEP (National Centers for Environmental Prediction) at the northern boundary of the model domain. Data from this model will be used to investigate the precipitation regime of DML, with emphasis on the following questions: Which synoptic situation brings the mosthe least precipitation to which areas? How does the sea ice extent influence temporal and spatial precipitation distribution? Are there constant orographical/precipitation shadow effects? Data from Automatical Weather Stations (AWS), accumulation data from traverses and from the cores will be used to verify the model precipitation. This should yield the first-ever detailed precipitation map of DML. As a next step, the accumulation and stable isotope data (the latter closely related to air temperature) from the shallow firn cores will be investigated in two different approaches: Since the core data show a considerable amount of noise due to high spatial variability of both accumulation rates and stable isotope ratios, a synthesis of all available cores using statistical methods is planned in order to get the most exact climatic information. In spite of the uncertainties mentioned above, there are systematic differences between the cores that can be identified and explained. This will be investigated using the single cores independently. Special attention will be given to the search for possible bias in the isotope profiles due to changes in the temporal distribution of accumulation, which depend on sea ice extent (data available from National Snow and Ice Data Center (NSIDC), Boulder, CO), storm tracks and cyclone frequency. The latter can be derived from ECMWF (European Centre for Medium-Range Weather Forecasts) re-analysis data. In particular, the coastal cores are of high interest because of the relatively high accumulation rates, which make it easier to find correlations with other parameters, especially sea ice extent. These two parts of the project are closely interrelated and it is expected that the results of both approaches influence each other, thus these studies will be done in parallel. The results of the proposed investigation will reduce the error possibilities in the climatic interpretation of the deep EPICA-DML core and provide realistical basic assumptions for GCM (General Atmospheric Circulation Model) studies in combination with data from this ice core.