Multi-scale variations of subglacial hydro-mechanical conditions at Kongsvegen glacier, Svalbard

The flow of glaciers is largely controlled by changes at the ice–bed interface, where basal slip and sediment deformation drive basal glacier motion. Determining subglacial conditions and their responses to hydraulic forcing remains challenging due to the difficulty of accessing the glacier bed. Here, we monitor the interplay between surface runoff and hydro-mechanical conditions at the base of the Kongsvegen glacier in Svalbard. From July 2021 to August 2022, we measured both subglacial water pressure and till strength. Additionally, we derived median values of subglacial hydraulic gradient and radius of channelized subglacial drainage system from seismic power, recorded at the glacier surface. To characterize the variations in the subglacial conditions caused by changes in surface runoff, we investigate the variations of the following hydro-mechanical properties: measured water pressure, measured sediment ploughing forces, and derived hydraulic gradient and radius, over seasonal, multi-day, and diurnal timescales. We discuss our results in light of existing theories of subglacial hydrology and till mechanics to describe subglacial conditions. We find that during the short, low-melt-rate season in 2021, the subglacial drainage system evolved at equilibrium with runoff, increasing its capacity as the melt season progressed. In contrast, during the long and high-melt-rate season in 2022, the subglacial drainage system evolved transiently to respond to the abrupt and large water supply. We suggest that in the latter configuration, the drainage capacity of the preferential drainage axis was exceeded, promoting the expansion of hydraulically connected regions and local weakening of ice–bed coupling and, hence, enhanced sliding.</p

Enquête exploratoire pour la mise en place d'un projet de recherche sur les connaissances et les attitudes des populations relatives à l'impact des activités industrielles sur la santé

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NMR and CD conformational studies of the C-terminal 16-peptides of Pseudomonas aeruginosa c(551) and Hydrogenobacter thermophilus c(552) cytochromes

The 16-amino acid sequences of the C-terminal helices of the homologous bacterial cytochromes C-551 from Pseudomonas aeruginosa and C-552 from Hydrogenobacter thermophilus were synthesized and their solution structure studied. Circular dichroism and NMR experiments in aqueous solution have shown the presence of alpha -helices and 3(10)-helices. The populations of helical structures in phosphate buffer, pH 3.5, 293 K, were 21% for C-551 and 20% for C-552, but increased to 56.7 and 48%, respectively, in 50% aqueous 2,2,2-trifluoroethanol. An isodichroic point was observed at 203 nm in CD spectra for the helix/coil transition in mixtures of water/2, 2,2-trifluoroethanol. NMR spectra in phosphate buffer show the presence of both alpha- and 3(10)-helical structures. In water/2,2,2-trifluoroethanol (50:50) alpha -helices are predominant. CD temperature-dependency studies indicate that both peptides exhibit the same cooperativity for the transition in waterl 2,2,2-trifluoroethanol (50:50). The experimental data show that the amino acid substitutions do not favor heat resistance of the secondary structure of the C-552 C-terminal helix at the local level. Instead, they optimize nonlocal contacts of the polypeptide chain, which stabilize the tertiary structure in the native protein