Marine pelagic ecosystems: the West Antarctic Peninsula

The marine ecosystem of the West Antarctic Peninsula (WAP) extends from the Bellingshausen Sea to the northern tip of the peninsula and from the mostly glaciated coast across the continental shelf to the shelf break in the west. The glacially sculpted coastline along the peninsula is highly convoluted and characterized by deep embayments that are often interconnected by channels that facilitate transport of heat and nutrients into the shelf domain. The ecosystem is divided into three subregions, the continental slope, shelf and coastal regions, each with unique ocean dynamics, water mass and biological distributions. The WAP shelf lies within the Antarctic Sea Ice Zone (SIZ) and like other SIZs, the WAP system is very productive, supporting large stocks of marine mammals, birds and the Antarctic krill, Euphausia superba. Ecosystem dynamics is dominated by the seasonal and interannual variation in sea ice extent and retreat. The Antarctic Peninsula is one among the most rapidly warming regions on Earth, having experienced a 28C increase in the annual mean temperature and a 68C rise in the mean winter temperature since 1950. Delivery of heat from the Antarctic Circumpolar Current has increased significantly in the past decade, sufficient to drive to a 0.68C warming of the upper 300 m of shelf water. In the past 50 years and continuing in the twenty-first century, the warm, moist maritime climate of the northern WAP has been migrating south, displacing the once dominant cold, dry continental Antarctic climate and causing multi-level responses in the marine ecosystem. Ecosystem responses to the regional warming include increased heat transport, decreased sea ice extent and duration, local declines in icedependent Ade´lie penguins, increase in ice-tolerant gentoo and chinstrap penguins, alterations in phytoplankton and zooplankton community composition and changes in krill recruitment, abundance and availability to predators. The climate/ecological gradients extending along theWAPand the presence of monitoring systems, field stations and long-term research programmes make the region an invaluable observatory of climate change and marine ecosystem response

Grain-boundary sliding and axial strain during diffusional creep

During diffusional creep, the grains of a polycrystal move relative to each other to maintain specimen coherency. This movement is analysed and it is shown that grain-boundary sliding and diffusion creep do not generally make separate contributions to the total creep strain

The dependence of grain-boundary sliding on shear stress

Polycrystalline specimens of four materials: aluminium, a lead/thallium alloy, /3-brass and Magnox AL80 were subjected to slow creep at a temperature of approximately 0.5 Tm (where Tm is the melting temperature in degrees Kelvin) and measurements made of the dependence of grain-boundary sliding on the orientation of the boundary with respect to the applied stress. The results were analysed in detail on the basis of the hypothesis that sliding is governed by the component of the applied stress resolved in the boundary plane. Agreement between theory and experiment leads to the conclusion that this is a most important factor governing sliding. The component of sliding revealed by steps on a free surface is seen to contain an extra term due to the unbalanced pressure from grains below the surface

Processing different magnesium alloys through HPT

High-Pressure Torsion (HPT) is widely used to refine the structure of metallic materials through the use of severe plastic deformation. This technique is used in this report to process different magnesium alloys using various processing conditions. The high hydrostatic pressure allows processing of these materials at room temperature without cracking. The structure was characterized and hardness distribution was determined at different areas of the processed samples. The results show significant structure refinement and increased hardness. The evolution of the structure and hardness depends on the alloying and HPT processing conditions.</jats:p

Compilation of non-annually resolved Holocene proxy climate records: stacked Holocene peatland palaeo-water table reconstructions from northern Britain

The number and range of Holocene palaeoclimate reconstructions from various regions of the world have increased dramatically over the last decade. The data density for many regions and proxies now offers the potential of robust regional-scale reconstructions that avoid the problems of records from individual sites, and improve communication between palaeoclimate subdisciplines and climate modellers. However, there are problems with chronological uncertainties and quantification of proxies, which make compilation of multiple records difficult. Here we explore a �stacking� and �tuning� approach to the derivation of regional records from peatland climate proxies to test its applicability to non-annually resolved terrestrial records. Twelve individual records from northern Britain based on water table reconstructions from testate amoebae analysis were divided into four regions. Records were detrended, normalised and compared within regions to identify clear correlative events. The original chronologies of the records were tuned using both these events and independent age markers. The stacked record for northern Britain indicates pronounced changes to wet conditions at 3600, 2760 and 1600 cal yr BP with more minor changes at 3060, 2050, 1260, 860, 550 and 260 cal yr BP. The main wet phases are highly correlated with mid-European lake highstands, wider North Atlantic climate change inferred from ocean and ice core records, and solar variability. Tuning and stacking of non-annual terrestrial palaeoclimate records is a new approach to the compilation and reconciliation of individual records within coherent climatic regions and provides a tool for upscaling of palaeoclimate records for climate model-data comparisons