TY - JOUR A1 - Laepple, Thomas A1 - Münch, Thomas A1 - Casado, Mathieu A1 - Hoerhold, Maria A1 - Landais, Amaelle A1 - Kipfstuhl, Sepp T1 - On the similarity and apparent cycles of isotopic variations in East Antarctic snow pits JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union N2 - Stable isotope ratios delta O-18 and delta D in polar ice provide a wealth of information about past climate evolution. Snow-pit studies allow us to relate observed weather and climate conditions to the measured isotope variations in the snow. They therefore offer the possibility to test our understanding of how isotope signals are formed and stored in firn and ice. As delta O-18 and delta D in the snowfall are strongly correlated to air temperature, isotopes in the near-surface snow are thought to record the seasonal cycle at a given site. Accordingly, the number of seasonal cycles observed over a given depth should depend on the accumulation rate of snow. However, snow-pit studies from different accumulation conditions in East Antarctica reported similar isotopic variability and comparable apparent cycles in the delta O-18 and delta D profiles with typical wavelengths of similar to 20 cm. These observations are unexpected as the accumulation rates strongly differ between the sites, ranging from 20 to 80mmw.e.yr(-1) (similar to 6-21 cm of snow per year). Various mechanisms have been proposed to explain the isotopic variations individually at each site; however, none of these are consistent with the similarity of the different profiles independent of the local accumulation conditions. Here, we systematically analyse the properties and origins of delta O-18 and delta D variations in high-resolution firn profiles from eight East Antarctic sites. First, we confirm the suggested cycle length (mean distance between peaks) of similar to 20 cm by counting the isotopic maxima. Spectral analysis further shows a strong similarity between the sites but indicates no dominant periodic features. Furthermore, the appar-ent cycle length increases with depth for most East Antarctic sites, which is inconsistent with burial and compression of a regular seasonal cycle. We show that these results can be explained by isotopic diffusion acting on a noise-dominated isotope signal. The firn diffusion length is rather stable across the Antarctic Plateau and thus leads to similar power spectral densities of the isotopic variations. This in turn implies a similar distance between isotopic maxima in the firn profiles. Our results explain a large set of observations discussed in the literature, providing a simple explanation for the interpretation of apparent cycles in shallow isotope records, without invoking complex mechanisms. Finally, the results underline previous suggestions that isotope signals in single ice cores from low-accumulation regions have a small signal-to-noise ratio and thus likely do not allow the reconstruction of interannual to decadal climate variations. Y1 - 2018 U6 - https://doi.org/10.5194/tc-12-169-2018 SN - 1994-0416 SN - 1994-0424 VL - 12 IS - 1 SP - 169 EP - 187 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Kokhanovsky, Alexander A1 - Lamare, Maxim A1 - Danne, Olaf A1 - Brockmann, Carsten A1 - Dumont, Marie A1 - Picard, Ghislain A1 - Arnaud, Laurent A1 - Favier, Vincent A1 - Jourdain, Bruno A1 - Le Meur, Emmanuel A1 - Di Mauro, Biagio A1 - Aoki, Teruo A1 - Niwano, Masashi A1 - Rozanov, Vladimir A1 - Korkin, Sergey A1 - Kipfstuhl, Sepp A1 - Freitag, Johannes A1 - Hoerhold, Maria A1 - Zuhr, Alexandra A1 - Vladimirova, Diana A1 - Faber, Anne-Katrine A1 - Steen-Larsen, Hans Christian A1 - Wahl, Sonja A1 - Andersen, Jonas K. A1 - Vandecrux, Baptiste A1 - van As, Dirk A1 - Mankoff, Kenneth D. A1 - Kern, Michael A1 - Zege, Eleonora A1 - Box, Jason E. T1 - Retrieval of Snow Properties from the Sentinel-3 Ocean and Land Colour Instrument JF - Remote sensing N2 - The Sentinel Application Platform (SNAP) architecture facilitates Earth Observation data processing. In this work, we present results from a new Snow Processor for SNAP. We also describe physical principles behind the developed snow property retrieval technique based on the analysis of Ocean and Land Colour Instrument (OLCI) onboard Sentinel-3A/B measurements over clean and polluted snow fields. Using OLCI spectral reflectance measurements in the range 400-1020 nm, we derived important snow properties such as spectral and broadband albedo, snow specific surface area, snow extent and grain size on a spatial grid of 300 m. The algorithm also incorporated cloud screening and atmospheric correction procedures over snow surfaces. We present validation results using ground measurements from Antarctica, the Greenland ice sheet and the French Alps. We find the spectral albedo retrieved with accuracy of better than 3% on average, making our retrievals sufficient for a variety of applications. Broadband albedo is retrieved with the average accuracy of about 5% over snow. Therefore, the uncertainties of satellite retrievals are close to experimental errors of ground measurements. The retrieved surface grain size shows good agreement with ground observations. Snow specific surface area observations are also consistent with our OLCI retrievals. We present snow albedo and grain size mapping over the inland ice sheet of Greenland for areas including dry snow, melted/melting snow and impurity rich bare ice. The algorithm can be applied to OLCI Sentinel-3 measurements providing an opportunity for creation of long-term snow property records essential for climate monitoring and data assimilation studies-especially in the Arctic region, where we face rapid environmental changes including reduction of snow/ice extent and, therefore, planetary albedo. KW - snow characteristics KW - optical remote sensing KW - snow grain size KW - specific surface area KW - albedo KW - Sentinel 3 KW - OLCI Y1 - 2019 U6 - https://doi.org/10.3390/rs11192280 SN - 2072-4292 VL - 11 IS - 19 PB - MDPI CY - Basel ER -