TY - JOUR A1 - Laepple, Thomas A1 - Hörhold, Maria A1 - Münch, Thomas A1 - Freitag, Johannes A1 - Wegner, Anna A1 - Kipfstuhl, Sepp T1 - Layering of surface snow and firn at Kohnen Station, Antarctica: Noise or seasonal signal? JF - Journal of geophysical research : Earth surface N2 - The density of firn is an important property for monitoring and modeling the ice sheets as well as to model the pore close-off and thus to interpret ice core-based greenhouse gas records. One feature, which is still in debate, is the potential existence of an annual cycle of firn density in low-accumulation regions. Several studies describe or assume seasonally successive density layers, horizontally evenly distributed, as seen in radar data. On the other hand, high-resolution density measurements on firn cores in Antarctica and Greenland show no clear seasonal cycle in the top few meters. A major caveat of most existing snow-pit and firn-core-based studies is that they represent one vertical profile from a laterally heterogeneous density field. To overcome this, we created an extensive data set of horizontal and vertical density data at Kohnen Station, Dronning Maud Land, on the East Antarctic Plateau. We drilled and analyzed three 90m long firn cores as well as 143 one-meter-long vertical profiles from two elongated snow trenches to obtain a two-dimensional view of the density variations. The analysis of the 45m wide and 1m deep density fields reveals a seasonal cycle in density. However, the seasonality is overprinted by strong stratigraphic noise, making it invisible when analyzing single firn cores. Our density data set extends the view from the local ice core perspective to a hundred meter scale and thus supports linking spatially integrating methods such as radar and seismic studies to ice and firn cores. Y1 - 2016 U6 - https://doi.org/10.1002/2016JF003919 SN - 2169-9003 SN - 2169-9011 VL - 121 SP - 1849 EP - 1860 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Münch, Thomas A1 - Kipfstuhl, Sepp A1 - Freitag, Johannes A1 - Meyer, Hanno A1 - Laepple, Thomas T1 - Regional climate signal vs. local noise: a two-dimensional view of water isotopes in Antarctic firn at Kohnen Station, Dronning Maud Land JF - Climate of the past : an interactive open access journal of the European Geosciences Union N2 - In low-accumulation regions, the reliability of delta O-18-derived temperature signals from ice cores within the Holocene is unclear, primarily due to the small climate changes relative to the intrinsic noise of the isotopic signal. In order to learn about the representativity of single ice cores and to optimise future ice-core-based climate reconstructions, we studied the stable-water isotope composition of firn at Kohnen Station, Dronning Maud Land, Antarctica. Analysing delta O-18 in two 50m long snow trenches allowed us to create an unprecedented, two-dimensional image characterising the isotopic variations from the centimetre to the 100-metre scale. Our results show seasonal layering of the isotopic composition but also high horizontal isotopic variability caused by local stratigraphic noise. Based on the horizontal and vertical structure of the isotopic variations, we derive a statistical noise model which successfully explains the trench data. The model further allows one to determine an upper bound for the reliability of climate reconstructions conducted in our study region at seasonal to annual resolution, depending on the number and the spacing of the cores taken. Y1 - 2016 U6 - https://doi.org/10.5194/cp-12-1565-2016 SN - 1814-9324 SN - 1814-9332 VL - 12 SP - 1565 EP - 1581 PB - Copernicus CY - Göttingen ER -