Structural characteristics of flow units in Svalbard valley glaciers and their utility for investigating ice-dynamic changes over centennial timescales

The aim of this paper is to characterise the internal structures and ice-flow history of representative valley glaciers in Svalbard, and infer from them dynamic changes over centennial timescales. Three polythermal and one cold valley glacier are investigated using field-and laboratory-based techniques, and remote sensing. Structures along flow-unit boundaries indicate that ice-flow configuration in three of the glaciers has remained stable spanning the residence time of the ice. Deformation of a flow-unit boundary in the fourth reveals an ice-flow instability, albeit one that has been maintained since its most recent advance. Macro-crystallographic, sedimentological, and isotopic analyses indicate that basal ice is elevated to the glacier surface, as shown by entrained sediments and enrichment in heavy isotopes. In narrow zones of enhanced cumulative strain, new ice facies are generated through dynamic recrystallization. The surface density of longitudinal foliation is shown to represent the relative magnitude of cumulative strain. Geometric similarities between flow-unit boundaries in Svalbard valley glaciers and larger scale longitudinal surface structures in ice sheets suggest that deformation mechanisms are common to both.