ALBERT

Description: Lake Towuti is a tectonic basin, surrounded by ultramafic rocks. Lateritic soils form through weathering and deliver abundant iron (oxy)hydroxides but very little sulfate to the lake and its sediment. To characterize the sediment biogeochemistry, we collected cores at three sites with increasing water depth and decreasing bottom water oxygen concentrations. Microbial cell densities were highest at the shallow site - a feature we attribute to the availability of labile organic matter and the higher abundance of electron acceptors due to oxic bottom water conditions. At the two other sites, OM degradation and reduction processes below the oxycline led to partial electron acceptor depletion. Genetic information preserved in the sediment as extracellular DNA provides information on aerobic and anaerobic heterotrophs related to Actinobacteria, Nitrospirae, Chloroflexi and Thermoplasmatales. These taxa apparently played a significant role in the degradation of sinking organic matter. However, extracellular DNA concentrations rapidly decrease with core depth. Despite very low sulfate concentrations, sulfate-reducing bacteria were present and viable in sediments at all three sites, as confirmed by measurement of potential sulfate reduction rates. Microbial community fingerprinting supported the presence of taxa related to Deltaproteobacteria and Firmicutes with demonstrated capacity for iron and sulfate reduction. Concomitantly, sequences of Ruminococcaceae, Clostridiales and Methanomicrobiales indicated potential for fermentative hydrogen and methane production. Such first insights into ferruginous sediments show that microbial populations perform successive metabolisms related to sulfur, iron and methane. In theory, iron reduction could reoxidize reduced sulfur compounds and desorb OM from iron minerals to allow remineralization to methane. Overall, we found that biogeochemical processes in the sediments can be linked to redox differences in the bottom waters of the three sites, like oxidant concentrations and the supply of labile OM. At the scale of the lacustrine record, our geomicrobiological study should provide a means to link the extant subsurface biosphere to past environments.

Description: Pore water geochemistry and bulk sediment measurements of downcore profiles covering the upper 100 m-long sequence from site 1A, Lake Towuti, Indonesia

Description: The airborne laser scanning (ALS) datasets were acquired at the Arctic tundra site of Trail Valley Creek (TVC), Northwest Territories, Canada, which is underlain by continuous permafrost. Basic processing and filtering steps were applied to the ALS point cloud. Based on a classification into ground and vegetation points, a Digital Terrain Model (DTM) and rasters of mean and maximum vegetation heights are derived. Detailed metadata are included.

Description: A major uncertainty in determining the mass balance of the Antarctic ice sheet from measurements of satellite gravimetry, and to a lesser extent satellite altimetry, is the poorly known correction for the ongoing deformation of the solid Earth caused by glacial isostatic adjustment (GIA). In the past decade, much progress has been made in consistently modelling the ice sheet and solid Earth interactions; however, forward-modelling solutions of GIA in Antarctica remain uncertain due to the sparsity of constraints on the ice sheet evolution, as well as the Earth's rheological properties. An alternative approach towards estimating GIA is the joint inversion of multiple satellite data - namely, satellite gravimetry, satellite altimetry and GPS, which reflect, with different sensitivities, trends of recent glacial changes and GIA. Crucial to the success of this approach is the accuracy of the space-geodetic data sets. Here, we present reprocessed rates of surface-ice elevation change (Envisat/ICESat; 2003-2009), gravity field change (GRACE; 2003-2009) and bedrock uplift (GPS; 1995-2013). The data analysis is complemented by the forward-modelling of viscoelastic response functions to disc load forcing, allowing us to relate GIA-induced surface displacements with gravity changes for different rheological parameters of the solid Earth. The data and modelling results presented here form the basis for the joint inversion estimate of present-day ice-mass change and GIA in Antarctica. This paper presents the first of two contributions summarizing the work carried out within a European Space Agency funded study, REGINA.

Description: The upper air soundings are normally performed once a day to measure vertical profiles of air pressure, temperature, relative humidity and the wind vector. Helium filled balloons (TOTEX 600 g, 800 g) were used to carry Vaisala RS92-SGPW radiosondes. Whenever possible, the launches were performed about 10 UTC. Condensed measurements (TEMP Format FM-35) were transferred without delay into the Global Telecommunication System GTS were they contribute for the world wide weather forecasts. The profile data were taken every 5-10 seconds which result in a vertical profile resolution of about 25-50 meter. The profiles start at the helideck 10 m above sea level and terminate at the burst level of the balloons, normally at heights between 25 and 37 km.

Description: Due to its strong influence on heat and moisture exchange between the ocean and the atmosphere, sea ice is an essential component of the global climate system. In the context of its alarming decrease in terms of concentration, thickness and duration, understanding the processes controlling sea-ice variability and reconstructing paleo-sea-ice extent in polar regions have become of great interest for the scientific community. In this study, for the first time, IP25, a recently developed biomarker sea-ice proxy, was used for a high-resolution reconstruction of the sea-ice extent and its variability in the western North Pacific and western Bering Sea during the past 18,000 years. To identify mechanisms controlling the sea-ice variability, IP25 data were associated with published sea-surface temperature as well as diatom and biogenic opal data. The results indicate that a seasonal sea-ice cover existed during cold periods (Heinrich Stadial 1 and Younger Dryas), whereas during warmer intervals (Bølling-Allerød and Holocene) reduced sea ice or ice-free conditions prevailed in the study area. The variability in sea-ice extent seems to be linked to climate anomalies and sea-level changes controlling the oceanographic circulation between the subarctic Pacific and the Bering Sea, especially the Alaskan Stream injection though the Aleutian passes.

Description: FIL2013: Polar 6 conducted a systematic digital photographic aerial survey of the area of the Filchner Outflow System during two survey flights from Halley VI on 15 and 16 November 2013. The total survey distance covered 3,000 km each on 15 (eastern section) and 16 (western section) November 2013. Due to a low cloud ceiling on 15 November, the first flight operation was terminated prematurely and thus the westernmost track could not be flown. This track was flown on 16 November, and the total number of tracks numbered 11 instead of 12 as had been planned originally. FIL2014: Visual surveys of pack ice seals using helicopters were conducted from 4 January to 9 February 2014 from aboard RV Polarstern (PS82). For all seal related operations (including deployments of satellite transmitte rs and reconnaissance flights) a total of 30:13 hours during 20 flights were flown (MIN 0:11; MAX 3:13). The survey region was sampled by flying systematically spaced line transects (parallel lines approximately 10 nm apart) whenever ship position and weather conditions allowed, with out clustering transects in areas of easier access. When a full transect length could not be flown on a day, we attempted to complete (extend) the particular transect on a following day.

Description: The upper air soundings are normally performed once a day to measure vertical profiles of air pressure, temperature, relative humidity and the wind vector. Helium filled balloons (TOTEX 600 g, 800 g) were used to carry Vaisala RS92-SGPW radiosondes. Whenever possible, the launches were performed about 10 UTC. Condensed measurements (TEMP Format FM-35) were transferred without delay into the Global Telecommunication System GTS were they contribute for the world wide weather forecasts. The profile data were taken every 5-10 seconds which result in a vertical profile resolution of about 25-50 meter. The profiles start at the helideck 10 m above sea level and terminate at the burst level of the balloons, normally at heights between 25 and 37 km.

Description: This dataset was created via processing of raw position data acquired by the GPS sensor for scientific equipment on Polar 6/Polar 5 to receive a validated master track which is used as reference of further expedition data.