Under-ice fauna, sea-ice concentration, sea-ice thickness and under-ice water parameters from the Eurasian central Arctic Ocean during POLARSTERN cruise ARK-XXVII/3 (PS80) in August-September 2012

Arctic sea-ice decline is expected to have a significant impact on Arctic marine ecosystems. Ice-associated fauna play a key role in this context because they constitute a unique part of Arctic biodiversity and transmit carbon from sea-ice algae into pelagic and benthic food webs. Our study presents the first regional-scale record of under-ice faunal distribution and the environmental characteristics of under-ice habitats throughout the Eurasian Basin. Sampling was conducted with a Surface and Under-Ice Trawl, equipped with a sensor array recording ice thickness and other physical parameters during trawling. We identified 2 environmental regimes, broadly coherent with the Nansen and Amundsen Basins. The Nansen Basin regime was distinguished from the Amundsen Basin regime by heavier sea-ice conditions, higher surface salinities and higher nitrate + nitrite concentrations. We found a diverse (28 species) under-ice community throughout the Eurasian Basin. Change in community structure reflected differences in the relative contribution of abundant species. Copepods (Calanus hyperboreus and C. glacialis) dominated in the Nansen Basin regime. In the Amundsen Basin regime, amphipods (Apherusa glacialis, Themisto libellula) dominated. Polar cod Boreogadus saida was present throughout the sampling area. Abrupt changes from a dominance of ice-associated amphipods at ice-covered stations to a dominance of pelagic amphipods (T. libellula) at nearby ice-free stations emphasised the decisive influence of sea ice on small-scale patterns in the surface-layer community. The observed response in community composition to different environmental regimes indicates potential long-term alterations in Arctic marine ecosystems as the Arctic Ocean continues to change.

Ice thickness measurements on South Tyrolean glaciers 1996-2014

The ice thickness of 15 South Tyrolean glaciers has been surveyed with two different types of radar systems between 1996 and 2014 within various research projects. For all glaciers apart from Weissbrunnferner, the Laser scan DEMs of the South Tyrolean glacier inventories had been taken as basis for the data processing. Earlier data has been measured with the Narod Sensor using a central frequency of 6.5 MHz, later data was recorded with a GSSI SIR 3000 system. The positions have been measured with a Garmin handheld GPS. The snow height at the time of the measurement was recorded by snow probing. The majority of the glaciers have been surveyed between 2009 and 2014, 9 glaciers in the year 2013. The methods for measurements and calculation of ice thickness are described in the various reports.

(Table 2) Observations of anticyclonic lenses of Mediterranean water in the Central North Atlantic

Analyses of spatial structure of hydrophysical fields and its vertical evolution in the Northeast Atlantic in a layer from the surface down to 2-2.5 km are carried out based on results of measurements in a testing area (31°-36°N, 20°-26°W) southeast of the Azores in autumn 1993. A description of an anti-cyclonic lens (ACL) of Mediterranean water (MW), which was found in the eastern part of the testing area from data of sets of sequential surveys, is presented. Analysis of CTD and XBT measurements in an area west of the lens allows to conclude that despite some contraction of width of the Azores Current directed eastward (from 60-80 km to 50-60 km) its total eastward volume transport for a period of time from October to November does not vary much. It is shown that intermediate salinity maxima in the northern part of the testing area formed by advection of MW and meddy destruction weakens while intersecting the Azores frontal zone (AFZ) from north to south, displacing itself to larger depth, and increases in thickness. Analysis of data shows that the number of lenses observed within the selected area north of the AFZ is two times more than that observed south of it. North of the AFZ observed salinity maximum and local temperature maxima may be associated with accumulation of heat and salt because of the fact that the AFZ is not only a southern boundary of penetration of MW into the North Atlantic, but also is a "semitransparent" boundary for Mediterranean lenses.

Photosynthetic production in the Central Arctic during POLARSTERN cruise ARK-XXVII/3 (IceArc) in 2012

The ice-covered Central Arctic Ocean is characterized by low primary productivity due to light and nutrient limitations. It has been speculated that the recent reduction in ice cover could lead to a substantial increase in primary production, but still little is known as to the fate of the ice-associated primary production, and of nutrient supply with increasing warming. This study presents results from the Central Arctic Ocean collected during summer 2012, when sea-ice reached a minimum extent since the onset of satellite observations. Net primary productivity (NPP) was measured in water column, sea ice and melt ponds by 14CO2 uptake at different irradiances. Photosynthesis vs. irradiance (PI) curves were established in laboratory experiments and used to upscale measured NPP to the deep Eurasian Basin (north of 78°N) using the irradiance-based Central Arctic Ocean Primary Productivity model (CAOPP). In addition, new annual production was calculated from the seasonal nutrient drawdown in the mixed layer since last winter. Results show that ice algae can contribute up to 60% to primary production in the Central Arctic at the end of the season. The ice-covered water column had lower NPP rates than open water probably due to light limitation. According to the nutrient ratios in the euphotic zone, nitrate limitation was detected in the Siberian Seas (Laptev Sea area), while silicate was the main limiting nutrient at the ice margin influenced by Atlantic waters. Although sea-ice cover was substantially reduced in 2012, total annual new production in the Eurasian Basin was 17 ± 7 Tg C/yr, which is similar to previous estimates. However, when including the contribution by sub-ice algal filaments, the annual production for the deep Eurasian Basin (north of 78°N) is 16 Tg C/yr higher than estimated before. Our data suggest that sub-ice algae might be responsible for potential local increases in NPP due to higher light availability under the ice, and their ability to benefit from a wider area of nutrients as they drift with the ice.

Phenotypic evolution in a venerid bivalve species lineage from the late Middle Miocene Central Paratethys Sea: a multi-approach morphometric analysis

A morphometric analysis was performed for the late Middle Miocene bivalve species lineage of Polititapes tricuspis (Eichwald, 1829) (Veneridae: Tapetini). Specimens from various localities grouped into two stratigraphically successive biozones, i.e. the upper Ervilia Zone and the Sarmatimactra Zone, were investigated using a multi-method approach. A Generalized Procrustes Analysis was computed for fifteen landmarks, covering characteristics of the hinge, muscle scars, and pallial line. The shell outline was separately quantified by applying the Fast Fourier Transform, which redraws the outline by fitting in a combination of trigonometric curves. Shell size was calculated as centroid size from the landmark configuration. Shell thickness, as not covered by either analysis, was additionally measured at the centroid. The analyses showed significant phenotypic differentiation between specimens from the two biozones. The bivalves become distinctly larger and thicker over geological time and develop circular shells with stronger cardinal teeth and a deeper pallial sinus. Data on the paleoenvironmental changes in the late Middle Miocene Central Paratethys Sea suggest the phenotypic shifts to be functional adaptations. The typical habitats for Polititapes changed to extensive, very shallow shores exposed to high wave action and tidal activity. Caused by the growing need for higher mechanical stability, the bivalves produced larger and thicker shells with stronger cardinal teeth. The latter are additionally shifted towards the hinge center to compensate for the lacking lateral teeth and improve stability. The deepening pallial sinus is related to a deeper burrowing habit, which is considered to impede being washed out in the new high-energy settings.