On 1 December 2011 the West Antarctic Ice Sheet (WAIS) Divide ice-core project reached its final depth of 3405 m. The WAIS Divide ice core is not only the longest US ice core to date, but is also the highest-quality deep ice core, including ice from the brittle ice zone, that the US has ever recovered. The methods used at WAIS Divide to handle and log the drilled ice, the procedures used to safely retrograde the ice back to the US National Ice Core Laboratory (NICL) and the methods used to process and sample the ice at the NICL are described and discussed.

Subglacial lakes beneath Antarctica’s fast-moving ice streams are known to undergo ∼1 km3 volume changes on annual timescales. Focusing on the MacAyeal Ice Stream (MacIS) lake system, we create a simple model for the response of subglacial water distribution to lake discharge events through assimilation of lake volume changes estimated from Ice, Cloud and land Elevation Satellite (ICESat) laser altimetry. We construct a steady-state water transport model in which known subglacial lakes are treated as either sinks or sources depending on the ICESat-derived filling or draining rates. The modeled volume change rates of five large subglacial lakes in the downstream portion of MacIS are shown to be consistent with observed filling rates if the dynamics of all upstream lakes are considered. However, the variable filling rate of the northernmost lake suggests the presence of an undetected lake of similar size upstream. Overall, we show that, for this fast-flowing ice stream, most subglacial lakes receive >90% of their water from distant distributed sources throughout the catchment, and we confirm that water is transported from regions of net basal melt to regions of net basal freezing. Our study provides a geophysically based means of validating subglacial water models in Antarctica and is a potential way to parameterize subglacial lake discharge events in large-scale ice-sheet models where adequate data are available.

Understanding the interaction between atomic hydrogen and solid tungsten is important for the development of fusion reactors in which proposed tungsten walls would be bombarded with high energy particles including hydrogen isotopes. Here, we report results from periodic density-functional theory calculations for three crucial aspects of this interaction: surface-to-subsurface diffusion of H into W, trapping of H at vacancies, and H-enhanced decohesion, with a view to assess the likely extent of hydrogen isotope incorporation into tungsten reactor walls. We find energy barriers of (at least) 2.08 eV and 1.77 eV for H uptake (inward diffusion) into W(001) and W(110) surfaces, respectively, along with very small barriers for the reverse process (outward diffusion). Although H dissolution in defect-free bulk W is predicted to be endothermic, vacancies in bulk W are predicted to exothermically trap multiple H atoms. Furthermore, adsorbed hydrogen is predicted to greatly stabilize W surfaces such that decohesion (fracture) may result from high local H concentrations.

Effective inhibitors of matrix metalloproteinases (MMPs), a family of connective tissue-degrading enzymes, could be useful for the treatment of diseases such as cancer, multiple sclerosis, and arthritis. Many of the known MMP inhibitors are derived from peptide substrates, with high potency in vitro but little selectivity among MMPs and poor bioavailability. We have discovered nonpeptidic MMP inhibitors with improved properties, and report here the crystal structures of human stromelysin-1 catalytic domain (SCD) complexed with four of these inhibitors. The structures were determined and refined at resolutions ranging from 1.64 to 2.0 Å. Each inhibitor binds in the active site of SCD such that a bulky diphenyl piperidine moiety penetrates a deep, predominantly hydrophobic S′1 pocket. The active site structure of the SCD is similar in all four inhibitor complexes, but differs substantially from the peptide hydroxamate complex, which has a smaller side chain bound in the S′1 pocket. The largest differences occur in the loop forming the “top” of this pocket. The occupation of these nonpeptidic inhibitors in the S′1 pocket provides a structural basis to explain their selectivity among MMPs. An analysis of the unique binding mode predicts structural modifications to design improved MMP inhibitors.

Morphologic discrimination of species of scleractinian reef corals has long been plagued by a shortage of independent characters and by high ecophenotypic plasticity. Because of these two factors, many species appear to intergrade morphologically. We outline a newly developed protocol for the morphometric recognition of species, which uses size and shape coordinates derived from landmark data. The landmarks consist of spatially homologous points digitized in three dimensions on upper calical surfaces. The approach is more powerful than linear measurements at detecting subtle distinctions among species; and the distinctions are easy to visualize and interpret biologically, which increases the accuracy and resolution of subsequent phylogenetic and large-scale faunal analyses.

As an example, we distinguish morphospecies in collections of Porites made at three Caribbean locations. Size and shape coordinates are analyzed using principal component analysis, average linkage cluster analysis, and a series of iterative discriminant analyses. Positions of different corallites from the same colonies are examined on cluster dendrograms to determine cutoffs for group recognition, and discriminant classifications for different corallites from the same colonies are compared to maximize group assignments. The results yield seven morphospecies, which are generally in 90% agreement with classification of the same animals using allozyme electrophoresis. Measures of corallite size and the relative heights and locations of the pali and septal denticles all reveal unique patterns of variation among morphospecies.

The Preceding discussions have considered the radiocarbon dates in relation to a number of archaeological, geological, and palynological problems. It remains to consider the endeavor as a whole, and to reach some conclusions concerning its present and future value and usefulness. Of primary importance is a consideration of what the dates mean. Basic to this is an understanding of the statistics involved. At the request of the Committee, Arnold, who has been intimately associated with the project, has kindly contributed the following explanatory paragraphs:

It seems worth while to review briefly the physical scientist's notions about the errors inherent in such measurements, as they apply to radiocarbon dates.