ABSTRACT. During an ice-tank experiment, samples were taken to study the processes of acquisition and alteration of the gas properties in young first-year sea ice during a complete growth^warming^cooling cycle. The goal was to obtain reference levels for total gas content and concentrations of atmospheric gases (O 2 , N 2 , CO 2 ) in the absence of significant biological activity. The range of total gas-content values obtained (3.5^18 mL STP kg^1) was similar to previous measurements or estimates. However, major differences occurred between current and quiet basins, showing the role of the water dynamics at the ice^water interface in controlling bubble nucleation processes. Extremely high CO 2 concentrations were observed in all the experiments (up to 57% in volume parts). It is argued that these could have resulted from two unexpected biases in the experimental settings. Concentrations in bubbles nucleated at the interface are controlled by diffusion both from the ice^water interface towards the wellmixed reservoir and between the interface water and the bubble itself.This double kinetic effect results in a transition of the gas composition in the bubbles from values close to solubility in sea water toward values close to atmospheric, as the ice cover builds up. FRAMEWORKThe impact of sea ice on the ocean^atmosphere^biosphere interactions in the polar regions is well recognized. Annual growth of a continuous sea-ice cover is considered to impede gaseous exchanges with the atmosphere so efficiently that global coupled models either assume a yes/no scenario, respectively, for absence/presence of sea ice (England and others, 1994; Dixon and others, 1996), or, more recently (Goosse and others, 1999), reduce winter exchanges to thè`l ead'' areas (open-water fraction, generally <10%, of the total area covered with sea ice in mid-winter). However, since for temperatures higher than roughly^5³C a marked transition is assumed to occur toward increased permeability for inclusions in sea ice (Weeks and Ackley, 1986; Golden and others, 1998), this should allow, in both autumn and spring, gas transfer between the ocean and the atmosphere across the sea-ice cover mainly via the brine-channel network. On the other hand, recent studies of the biogeochemistry of the sea-ice habitat others,1995,1996) have shown that under favourable circumstances such as summer algal blooms, biological activity can profoundly affect the brine geochemistry, including the gaseous components. This has important implications for pathways of algal carbon acquisition (and therefore ice-algal species succession during summer blooms), carbon isotope fractionation and species distribution in the open-water phytoplankton. These two examples point to the need for a better understanding of the behaviour of the gaseous components of sea ice, both as gas bubbles and dissolved in brines.Datasets on total gas content and gas composition of sea ice are scarce. To our knowledge, only two attempts, both in the mid-1960s, have been made to measure gas propertie...

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Background and aims : Vegetation can be used to stabilise slopes with regard to shallow landslides, but the optimal plant architecture for conferring resistance is not known. This study aims at identifying root morphological traits which confer the most resistance to soil during shearing.Methods : Three species used for slope stabilisation (Ricinus communis L., Jatropha curcas L. and Rhus chinensis Mill.) were grown for 10 months in large shear boxes filled with silty clay similar to that found in Yunnan, China. Direct shear tests were then performed and compared to fallow soil. Root systems were excavated and a large number of traits measured.Results : Shear strength and deformation energy were enhanced by the presence of roots. Regardless of confining pressure, R. communis conferred most resistance due to its taprooted system with many vertical roots. J. curcas possessed oblique and vertical roots which created fragile zones throughout the soil profile. The least efficient root system was R. chinensis which possessed many horizontal lateral roots. Soil mechanical properties were most influenced by (i) density of roots crossing the shear plane, (ii) branching density throughout the soil profile, (iii) total length of coarse roots above the shear plane and (iv) total volume of coarse roots and fine root density below the shear plane. During failure, fine, short and branched roots slipped through soil rather than breaking.Conclusion : Root morphological traits such as density, branching, length, volume, inclination and orientation influence significantly soil mechanical propertie

Kawah Ijen is a composite volcano located at the easternmost part of Java island in Indonesia and hosts the largest natural acidic lake in the world. We have gathered all available historical reports on Kawah Ijen's activity since 1770 with the purpose of reviewing the temporal evolution of its activity. Most of these observations and studies have been conducted from a geochemical perspective and in punctuated scientific campaigns. Starting in 1991, the seismic activity and a set of volcanic lake parameters began to be weekly available. We present a database of those measurements that, combined with historical reports, allow us to review each eruption/unrest that occurred during the last two centuries. As of 2010, the volcanic activity is monitored by a new multi-disciplinary network, including digital seismic stations, and lake level and temperature measurements. This detailed monitoring provides an opportunity for better Editorial responsibility: G. Giordano C. Caudron ( ) ·

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Remotely sensed measurements of sulphur dioxide (SO 2 ) emitted by Turrialba Volcano (Costa Rica) are reported for the period September 2009-January 2011. These measurements were obtained using images from Advanced Spaceborne Thermal Emission and Reflexion radiometer, Ozone Monitoring Instrument and a ground-based UV camera. These three very different instruments provide flux measurements in good agreement with each other, which demonstrate that they can be integrated for monitoring SO 2 fluxes. Fluxes from Turrialba increased fourfold in January 2010, following a phreatic explosion that formed a degassing vent in the W crater of Turrialba. Since then, the SO 2 flux has remained high (30-50 kg/s) but seems to be showing a slowly decreasing trend. We interpret this evolution as the start of open vent degassing from a recently intruded magma body. The opening of the degassing vent decreased the confining pressure of the magma body and allowed the gases to bypass the hydrothermal system.

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