Water and the density of silicate glasses

A review of published and newly measured densities for 40 hydrous silicate glasses indicates that the room-temperature partial molar volume of water is 12.0 ± 0.5 cm³/mol. This value holds for simple or mineral compositions as well as for complex natural glasses, from rhyolite to tephrite compositions, prepared up to 10–20 kbar pressures and containing up to 7 wt% H₂O. This volume does not vary either with the molar volume of the water-free silicate phase, with its degree of polymerization or with water speciation. Over a wide range of compositions, this constant value implies that the volume change for the reaction between hydroxyl ions and molecular water is zero and that, at least in glasses, speciation does not depend on pressure. Consistent with data from Ochs and Lange (1997, 1999), systematics in volume expansion for SiO₂–M₂O systems (M=H, Li, Na, K) suggests that the partial molar thermal expansion coefficient of H₂O is about 4 × 10⁻⁵ K⁻¹ in silicate glasses. Received: 30 June 1999 / Accepted: 5 November 1999     

The 10Be deglaciation chronology of the Göschenertal,central Swiss Alps,and new insights into the Göschenen Cold Phases

The Göschenertal (Göschenen valley) is the type locality of the so‐called Göschenen Cold Phases I (~3–2.3 ka) and II (~1.8–1.1 ka). According to earlier studies, these Late Holocene climatic cooling periods were characterized by changes in vegetation and pronounced glacier advances. As a peculiarity, the Göschenen Cold Phase I was thought to be connected to a local surge‐type advance of the Chelengletscher (Chelen glacier) – an exceptional event of unparalleled dimension in the European Alps. Based on cosmogenic ¹⁰Be exposure ages from moraine boulders, we investigated the local glacier chronology. In contrast to former research, moraines at different positions within the Göschenen valley (central Swiss Alps) have been dated to the Younger Dryas and the Early Holocene. This questions the applicability of palaeo‐Equilibrium Line Altitude (ELA) calculations for stadial attributions without additional numerical age constraints. Furthermore, we have found compelling evidence that the proposed non‐climatic glacier advance attributed to the Göschenen Cold Phase I did not occur. The present results, along with a reappraisal of the original study, question the scientific reliability and the glaciological definition of the Göschenen Cold Phases as glacier advances that clearly exceeded the Little Ice Age positions. While our data do not exclude potential changes in climate and vegetation, we nonetheless show that the Göschenen Cold Phases are not suitable as reference stadials in the system of Alpine Holocene glacier fluctuations.     

Decadal prediction skill in the GEOS-5 forecast system

A suite of decadal predictions has been conducted with the NASA Global Modeling and Assimilation Office’s (GMAO’s) GEOS-5 Atmosphere–Ocean general circulation model. The hind casts are initialized every December 1st from 1959 to 2010, following the CMIP5 experimental protocol for decadal predictions. The initial conditions are from a multi-variate ensemble optimal interpolation ocean and sea-ice reanalysis, and from GMAO’s atmospheric reanalysis, the modern-era retrospective analysis for research and applications. The mean forecast skill of a three-member-ensemble is compared to that of an experiment without initialization but also forced with observed greenhouse gases. The results show that initialization increases the forecast skill of North Atlantic sea surface temperature compared to the uninitialized runs, with the increase in skill maintained for almost a decade over the subtropical and mid-latitude Atlantic. On the other hand, the initialization reduces the skill in predicting the warming trend over some regions outside the Atlantic. The annual-mean atlantic meridional overturning circulation index, which is defined here as the maximum of the zonally-integrated overturning stream function at mid-latitude, is predictable up to a 4-year lead time, consistent with the predictable signal in upper ocean heat content over the North Atlantic. While the 6- to 9-year forecast skill measured by mean squared skill score shows 50 % improvement in the upper ocean heat content over the subtropical and mid-latitude Atlantic, prediction skill is relatively low in the subpolar gyre. This low skill is due in part to features in the spatial pattern of the dominant simulated decadal mode in upper ocean heat content over this region that differ from observations. An analysis of the large-scale temperature budget shows that this is the result of a model bias, implying that realistic simulation of the climatological fields is crucial for skillful decadal forecasts.     

The Community Economic Impacts of Large Wildfires: A Case Study from Trinity County,California

Wildfires are increasing in severity and frequency in the American West, but there is limited understanding of their economic effects at the community level. We conducted a case study of the impacts of large wildfires in 2008 in Trinity County, California, by examining labor market, suppression spending, and qualitative interview data. We found that the 2008 fires had interrelated effects on several economic sectors in the county. Labor market data indicated a decrease in total private-sector employment and wages and an increase in public-sector employment and wages during the summer of 2008 compared to the previous year, while interviews captured more nuanced impacts for individual businesses.     

Sea-floor methane blow-out and global firestorm at the K–T boundary

 A previously unsuspected source of fuel for the global firestorm recorded by soot in the Cretaceous–Tertiary impact layer may have resided in methane gas associated with gas hydrate in the end-Cretaceous seafloor. End-Cretaceous impact-generated shock and megawaves would have had the potential to initiate worldwide oceanic methane gas blow-outs from these deposits. The methane would likely have ignited and incompletely combusted. This large burst of methane would have been followed by longer-term methane release as a part of a positive thermal feedback in the disturbed ocean-atmosphere system. Received: 16 September 1998 / revision received: 11 January 1999     

Das südliche Rheintal an der Zeitwende von Rhät und Lias

Ohne Zusammenfassung     

The large-scale polarization of the microwave foreground

Most of the useful information about inflationary gravitational waves and reionization is on large angular scales where Galactic foreground contamination is the worst, so a key challenge is to model, quantify and remove polarized foregrounds. We use the Leiden radio surveys to quantify the polarized synchrotron radiation at large angular scales, which is likely to be the most challenging polarized contaminant for the WMAP satellite. We find that the synchrotron E- and B-contributions are equal to within 10% from 408–820 MHz with a hint of E-domination at higher frequencies. We quantify Faraday rotation and depolarization effects and show that they cause the synchrotron polarization percentage to drop both towards lower frequencies and towards lower multipoles.