Five decades of terrestrial and freshwater research at Ny-Ålesund, Svalbard

For more than five decades, research has been conducted at Ny-Ålesund, in Svalbard, Norway, to understand the structure and functioning of High-Arctic ecosystems and the profound impacts on them of environmental change. Terrestrial, freshwater, glacial and marine ecosystems are accessible year-round from Ny-Ålesund, providing unique opportunities for interdisciplinary observational and experimental studies along physical, chemical, hydrological and climatic gradients. Here, we synthesize terrestrial and freshwater research at Ny-Ålesund and review current knowledge of biodiversity patterns, species population dynamics and interactions, ecosystem processes, biogeochemical cycles and anthropogenic impacts. There is now strong evidence of past and ongoing biotic changes caused by climate change, including negative effects on populations of many taxa and impacts of rain-on-snow events across multiple trophic levels. While species-level characteristics and responses are well understood for macro-organisms, major knowledge gaps exist for microbes, invertebrates and ecosystem-level processes. In order to fill current knowledge gaps, we recommend (1) maintaining monitoring efforts, while establishing a long-term ecosystem-based monitoring programme; (2) gaining a mechanistic understanding of environmental change impacts on processes and linkages in food webs; (3) identifying trophic interactions and cascades across ecosystems; and (4) integrating long-term data on microbial, invertebrate and freshwater communities, along with measurements of carbon and nutrient fluxes among soils, atmosphere, freshwaters and the marine environment. The synthesis here shows that the Ny-Ålesund study system has the characteristics needed to fill these gaps in knowledge, thereby enhancing our understanding of High-Arctic ecosystems and their responses to environmental variability and change

High-velocity impact of solid objects on Non-Newtonian Fluids

Abstract We investigate which property of non-Newtonian fluids determines the deceleration of a high-speed impacting object. Using high-speed camera footage, we measure the velocity decrease of a high-speed spherical object impacting a typical Newtonian fluid (water) as a reference and compare it with a shear thickening fluid (cornstarch) and a shear thinning viscoelastic fluid (a weakly cross-linked polymer gel). Three models describing the kinetic energy loss of the object are considered: fluid inertia, shear thickening and viscoelasticity. By fitting the three models to the experimental data, we conclude that the viscoelastic model works best for both the cornstarch and the polymer gel. Since the cornstarch is also viscoelastic, we conclude that the ability to stop objects of these complex fluids is given by their viscoelasticity rather than shear thickening or shear thinning

Predicting the maximum spreading of a liquid drop impacting on a solid surface:Effect of surface tension and entrapped air layer

The spreading of liquid droplets impacting a surface at high speed is well understood by now. However, when a droplet impacts a surface at relatively low impact velocities (<1 m/s), the wetting properties of the fluid become important, and the entrapped air layer between the impacting drop and the solid surface prevents the immediate wetting of the surface. To determine the influence of both wetting and the entrapped air, we perform experiments by systematically varying the surface tension of the liquid and the air pressure. Drop impact measurements at reduced air pressures show that the spreading is independent of the pressure; dynamic contact-angle measurements indicate that this happens because the air film breaks rapidly. By varying the surface tension and surface wettability, we show that droplet spreading at low velocities can be predicted from the wetting properties of the surface and the known energy balance for the impact

Effect of Wetting on Drop Splashing of Newtonian Fluids and Blood

We investigate the impact velocity beyond which the ejection of smaller droplets from the main droplet (splashing) occurs for droplets of different liquids impacting different smooth surfaces. We examine its dependence on the surface wetting properties and droplet surface tension. We show that the splashing velocity is independent of the wetting properties of the surface but increases roughly linearly with increasing surface tension of the liquid. A preexisting splashing model and simplification are considered that predict the splashing velocity by incorporating the air viscosity. Both the splashing model and simplification give a good prediction of the splashing velocity for each surface and liquid, demonstrating the robustness of the splashing model. We also show that the splashing model can also predict the splashing velocity of blood, a shear-thinning fluid