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Water flowing below glaciers exerts a major control on glacier basal sliding. However, our knowledge of the physics of subglacial hydrology and its link with sliding is limited because of lacking observations. Here we use a 2-year-long dataset made of on-ice-measured seismic and in situ-measured glacier basal sliding speed on Glacier d'Argentière (French Alps) to investigate the physics of subglacial channels and its potential link with glacier basal sliding. Using dedicated theory and concomitant measurements of water discharge, we quantify temporal changes in channels' hydraulic radius and hydraulic pressure gradient. At seasonal timescales we find that hydraulic radius and hydraulic pressure gradient respectively exhibit a 2- and 6-fold increase from spring to summer, followed by comparable decrease towards autumn. At low discharge during the early and late melt season channels respond to changes in discharge mainly through changes in hydraulic radius, a regime that is consistent with predictions of channels' behaviour at equilibrium. In contrast, at high discharge and high short-term water-supply variability (summertime), channels undergo strong changes in hydraulic pressure gradient, a behaviour that is consistent with channels behaving out of equilibrium. This out-of-equilibrium regime is further supported by observations at the diurnal scale, which prove that channels pressurize in the morning and depressurize in the afternoon. During summer we also observe high and sustained basal sliding speed, which supports that the widespread inefficient drainage system (cavities) is likely pressurized concomitantly with the channel system. We propose that pressurized channels help sustain high pressure in cavities (and therefore high glacier sliding speed) through an efficient hydraulic connection between the two systems. The present findings provide an essential basis for testing the physics represented in subglacial hydrology and glacier sliding models., The Cryosphere, 14 (5), ISSN:1994-0416, ISSN:1994-0424

The ENVRI community (Environmental and Earth System Research Infrastructures) covers multiple scientific domains, such as oceanography, atmosphere, geophysics and biology. Whilst very different in terms of scope and technology, the research infrastructures and their personnel face common technical challenges related to the fact that field equipment is often installed in remote sites. Specifically, a large proportion of field equipment needs to be autonomous and sometimes operates in extreme conditions. Theme 1, “Technical innovation”, aims to provide and improve the technology used by environmental RIs by developing internal cooperation synergy and by collaborating with the industries that propose solutions for RIs. WP3, “Improving measurement networks: common technological solutions”, is focused on energy issues (WP3.1: Enhancing observation capacity in remote sites: improving energy production) and data transmission (WP3.3: Robust data provision: data transmission and near real time QC) in extreme environments (WP3.2: Testing robustness towards extreme conditions). This report deals with the work for WP3.1, which was conducted between 2015 and 2018, as a collaborative project involving CNRS EPOS, ANAEE and ACTRIS. The main questions for Task 3.1 were: - What is needed to provide energy to isolated scientific stations? - What are the most sustainable technical solutions regarding the specific needs of RIs? - What do RIs actually use? - How to improve RI use of these systems? The report gathers information on energy production and storage using land-based instruments. It contains advice for potential non-specialist users, with technical abstracts and data sheets on each technology. The report is the main outcome of Task 3.1, and is attached as ANNEX I. This deliverable has also benefitted from interaction with other ENVRI+ partners, and IFREMER’s contribution concerning energy solutions in marine environments, which can be found in ANNEX II. The report in ANNEX I is composed of five main chapters.