Investigating changes in basal conditions of Variegated Glacier prior to and during its 1982–1983 surge

Variegated Glacier (Alaska) is known to surge periodically after a sufficient amount of cumulative mass balance is reached, but this observation is difficult to link with changes in the basal conditions. Here, using a 10-yr dataset, consisting of surface topography and surface velocity observations along a flow line for 25 dates, we have reconstructed the evolution of the basal conditions prior to and during the 1982–1983 surge. The model solves the full-Stokes problem along the central flow line using the finite element method. For the 25 dates of the dataset, the basal friction parameter distribution is inferred using the inverse method proposed by Arthern and Gudmundsson (2010). This method is here slightly modified by incorporating a regularisation term in the cost function to avoid short wavelength changes in the friction parameter. Our results indicate that dramatic changes in the basal conditions occurred between 1973 to 1983. Prior to the surge, periodic changes can be observed between winter and summer, with a regular increase of the sliding from 1973 to 1982. During the surge, the basal friction decreased dramatically and an area of very low friction moved from the upper part of the glacier to its terminus. Using a more complex friction law, these changes in basal sliding are then interpreted in terms of basal water pressure. Our results support that dramatic changes took place in the subglacial drainage system of Variegated Glacier, moving from a relatively efficient drainage system prior to the surge to an inefficient one during the surge. By reconstructing the water pressure evolution at the base of the glacier it is possible to propose a scenario for the hydrological history leading to the occurrence of a surge

Optimal Operation of the Multireservoir System in the Seine River Basin Using Deterministic and Ensemble Forecasts

International audienceThis article investigates the improvement of the operation of a four-reservoir system in the Seine River basin, France, by use of deterministic and ensemble weather forecasts and real-time control. In the current management, each reservoir is operated independently from the others and following prescribed rule-curves, designed to reduce floods and sustain low flows under the historical hydrological conditions. However, this management system is inefficient when inflows are significantly different from their seasonal average and may become even more inadequate to cope with the predicted increase in extreme events induced by climate change. In this work, a centralized real-time control system is developed to improve reservoirs operation by exploiting numerical weather forecasts that are becoming increasingly available. The proposed management system implements a well-established optimization technique, model predictive control (MPC), and its recently modified version that can incorporate uncertainties, tree-based model predictive control (TB-MPC), to account for deterministic and ensemble forecasts respectively. The management system is assessed by simulation over historical events and compared to the no-forecasts strategy based on rule-curves. Simulation results show that the proposed real-time control system largely outperforms the no-forecasts management strategy, and that explicitly considering forecast uncertainty through ensembles can compensate for the loss in performance due to forecast inaccuracy

An Auxin Transport-Based Model of Root Branching in Arabidopsis thaliana

Root architecture is a crucial part of plant adaptation to soil heterogeneity and is mainly controlled by root branching. The process of root system development can be divided into two successive steps: lateral root initiation and lateral root development/emergence which are controlled by different fluxes of the plant hormone auxin. While shoot architecture appears to be highly regular, following rules such as the phyllotactic spiral, root architecture appears more chaotic. We used stochastic modeling to extract hidden rules regulating root branching in Arabidopsis thaliana. These rules were used to build an integrative mechanistic model of root ramification based on auxin. This model was experimentally tested using plants with modified rhythm of lateral root initiation or mutants perturbed in auxin transport. Our analysis revealed that lateral root initiation and lateral root development/emergence are interacting with each other to create a global balance between the respective ratio of initiation and emergence. A mechanistic model based on auxin fluxes successfully predicted this property and the phenotype alteration of auxin transport mutants or plants with modified rythms of lateral root initiation. This suggests that root branching is controlled by mechanisms of lateral inhibition due to a competition between initiation and development/emergence for auxin

The effect of sucrose on the development of hybrid walnut microcuttings (Juglans nigra x Juglans regia). Consequences on their survival during acclimatization

We studied the effect of sucrose concentration in the root-development medium on the formation of adventitious roots and survival of microcuttings during acclimatization in 2 interspecific hybrid walnut (Juglans nigra n° 23 x J regia) clones. Sucrose increased the rooting percentage (fig 1), the number of adventitious roots (fig 2A) and the dry-matter content (table I) per rooted shoot. These effects were due to the energy properties of sucrose rather than to its osmotic function. High sucrose concentrations in the root-development medium (> 20 g·l-1) resulted in a high soluble carbohydrate content in the plantlets (fig 3), mainly located in roots and callus. The 2 clones showed different capacities in rooting and growth. Survival of microcuttings during acclimatization was not directly influenced by the sucrose concentration (fig 5) but was correlated with the number of adventitious roots (fig 6A) as well as with the number of leaves (fig 6B) present at the time of transfer to the growth chamber for each individual plant.Rôle du saccharose sur le développement des microboutures de noyers hybrides (Juglans nigra x Juglans regia). Conséquences sur leur taux de survie en acclimatation. Nous avons étudié l'effet de la concentration en saccharose dans le milieu de développement racinaire sur la formation de racines adventives et la survie de 2 clones d'hybrides interspécifiques de noyer (Juglans nigra 23 x Juglans regia). Les expériences montrent que l'enracinement nécessite la présence de saccharose dans le milieu (fig 1). Le saccharose augmente à la fois le taux d'enracinement, le nombre de racines adventives (fig 2A) et la quantité de matière sèche (tableau I) par pousse enracinée. Cet effet du saccharose est à relier à ses propriétés énergétiques plus qu'à son rôle osmotique. Les concentra- tions élevées en saccharose dans le milieu de développement (> 20 g·l-1) induisent aussi une teneur élevée en sucres solubles dans les pousses enracinées (fig 3), essentiellement des racines et du cal. Les 2 clones montrent des différences d'enracinement et de croissance. La concentration en saccharose dans le milieu de développement n'a pas d'effet sur la survie des microboutures pendant la phase dacclimatation. La survie des pousses enracinées des 2 clones augmente avec le nombre de racines adventives (fig 6A) et avec le nombre de feuilles étalées (fig 6B) présentes au moment de la phase de transfert en chambre climatisée

Development of photosynthetic ability of hybrid walnut plantlets during acclimatization

International audienc

Rôle du saccharose sur le développement des microboutures de noyers hybrides (Juglans nigra x Juglans regia). Conséquences sur leur taux de survie en acclimatation

27 ref.International audienc

Carbon partitioning in walnut seedlings and microcuttings during the acquisition of autotrophy

National audienc