Morphology and size of Neogloboquadrina pachyderma in the North Atlantic

The variability in size and shape of shells of the polar planktonic foraminifer Neogloboquadrina pachyderma have been quantified in 33 recent surface sediment samples throughout the northern Atlantic Ocean and correlated with the properties of the ambient surface waters. The aim of the study was to determine whether any of the morphological features could be used to reconstruct sea surface properties in the polar realm of the North Atlantic, where most paleotemperature proxies appear to fail. The analyses revealed that shell morphology is only weakly controlled by habitat properties, whereas shell size showed a strong correlation with sea surface temperature. The regression of mean shell size on sea surface temperature revealed the presence of two trends among the sinistrally coiled shells: a continuous increase in shell size with decreasing SST in sediments deposited under polar water masses and a continuous increase in shell size with increasing SST in samples from transitional waters. The second trend mirrors the trend observed for dextrally coiled shells, which are frequent in the same samples and signal the presence of N. incompta. The identical mean shell size trends among the sinistral and dextral specimens in the temperate samples confirms the results of earlier genetic studies which indicated the existence of a small but distinct proportion of opposite coiling in N. incompta, to which the sinistral shells in the temperate samples could be attributed. The linear correlation between mean shell size and sea surface temperature in the polar domain (summer SST < 9 °C) has been used to develop an empirical formula for the reconstruction of past sea surface temperatures from shell sizes in fossil samples. The standard error of the residuals of the linear regression is 2.36 °C (1 sigma), which implies a much larger error than for most paleothermometers, but enough precision to allow resolution between results by individual paleothermometers in the polar domain. The resulting regression model has been applied on two sediment cores spanning the interval from the Last Glacial Maximum (LGM) to the present day. The results from core PS1906-1 are consistent with ice-free conditions during the LGM in the Norwegian Sea. The SST estimates for the LGM inferred from N. pachyderma shell size are similar or slightly higher than those for the latest Holocene. The results do not indicate anomalously high SST during the glacial and the LGM reconstructions thus appear more consistent with the results from foraminiferal transfer functions and geochemical proxies. Both sediment cores show the highest reconstructed SST during the early Holocene insolation optimum.

Wet tundra polygon centers and distance between polygon centroids on Samoylov Island, Lena Delta, Siberia, Russia, with links to shape files

Subgrid processes occur in various ecosystems and landscapes but, because of their small scale, they are not represented or poorly parameterized in climate models. These local heterogeneities are often important or even fundamental for energy and carbon balances. This is especially true for northern peatlands and in particular for the polygonal tundra, where methane emissions are strongly influenced by spatial soil heterogeneities. We present a stochastic model for the surface topography of polygonal tundra using Poisson-Voronoi diagrams and we compare the results with available recent field studies. We analyze seasonal dynamics of water table variations and the landscape response under different scenarios of precipitation income. We upscale methane fluxes by using a simple idealized model for methane emission. Hydraulic interconnectivities and large-scale drainage may also be investigated through percolation properties and thresholds in the Voronoi graph. The model captures the main statistical characteristics of the landscape topography, such as polygon area and surface properties as well as the water balance. This approach enables us to statistically relate large-scale properties of the system to the main small-scale processes within the single polygons.

Air photography Samoylov Island

For the qualitative description of surface properties like vegetation cover or land-water-ratio of Samoylov Island as well as for the evaluation of fetch homogeneity considerations of the eddy covariance measurements and for the up-scaling of chamber flux measurements, a detailed surface classification of the island at the sub-polygonal scale is necessary. However, up to know only grey-scale Corona satellite images from the 1960s with a resolution of 2 x 2 m and recent multi-spectral LandSat images with a resolution of 30 x 30 m were available for this region. Both are not useable for the desired classification because of missing spectral information and inadequate resolution, respectively. During the Lena 2003 expedition, a survey of the island by air photography was carried out in order to obtain images for surface classification. The photographs were taken from a helicopter on 10.07.2002, using a Canon EOS100 reflex camera, a Soligor 19-23 mm lens and colour slide film. The height from which the photographs were taken was approximately 600 meters. Due to limited flight time, not all the area of the island could be photographed and some regions could only be photographed with a slanted view. As a result, the images are of a varying quality and resolution. In Potsdam, after processing the films were scanned using a Nikon LS-2000 scanner at maximal resolution setting. This resulted in a ground resolution of the scanned images of approximately 0.3x0.3 m. The images were subsequently geo-referenced using the ENVI software and a referenced Corona image dating from 18.07.1964 (Spott, 2003). Geo-referencing was only possible for the Holocene river terrace areas; the floodplain regions in the western part of the island could not be referenced due to the lack of ground reference points. In Figure 3.7-1, the aerial view of Samoylov Island composed of the geo-referenced images is shown. Further work is necessary for the classification and interpretation of the images. If possible, air photography surveys will be carried out during future expeditions in order to determine changes in surface pattern and composition.

Solar radiation over and under sea ice at ROV station PS86/081-1 during POLARSTERN cruise PS86 (AURORA) in July 2014

The observed changes in physical properties of sea ice such as decreased thickness and increased melt pond cover severely impact the energy budget of Arctic sea ice. Increased light transmission leads to increased deposition of solar energy in the upper ocean and thus plays a crucial role for amount and timing of sea-ice-melt and under-ice primary production. Recent developments in underwater technology provide new opportunities to study light transmission below the largely inaccessible underside of sea ice. We measured spectral under-ice radiance and irradiance using the new Nereid Under-Ice (NUI) underwater robotic vehicle, during a cruise of the R/V Polarstern to 83°N 6°W in the Arctic Ocean in July 2014. NUI is a next generation hybrid remotely operated vehicle (H-ROV) designed for both remotely piloted and autonomous surveys underneath land-fast and moving sea ice. Here we present results from one of the first comprehensive scientific dives of NUI employing its interdisciplinary sensor suite. We combine under-ice optical measurements with three dimensional under-ice topography (multibeam sonar) and aerial images of the surface conditions. We investigate the influence of spatially varying ice-thickness and surface properties on the spatial variability of light transmittance during summer. Our results show that surface properties such as melt ponds dominate the spatial distribution of the under-ice light field on small scales (<1000 m**2), while sea ice-thickness is the most important predictor for light transmission on larger scales. In addition, we propose the use of an algorithm to obtain histograms of light transmission from distributions of sea ice thickness and surface albedo.