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Dewey Library - HJ1441.F54 2021

Is there a single surge mechanism? Contrasts in dynamics between glacier surges in Svalbard and other regions Murray, Tavi; Strozzi, Tazio; Luckman, Adrian; Jiskoot, Hester; Christakos, Panos During the 1990s, Monacobreen, a 40-km-long tidewater glacier in Svalbard, underwent a major surge. We mapped the surge dynamics using ERS synthetic aperture radar images, differential dual-azimuth interferometry and intensity correlation tracking. A series of 11 three-dimensional (3-D) velocity maps covering the period 1991–1997 show a months-long initiation and years-long termination to the surge, with no indication of a surge front travelling downglacier. During the surge, the front of the glacier advanced 2 km, the velocity and derived strain rate increased by more than an order of magnitude, and maximum ice flow rates measured during 1994 were 5md 1. The spatial pattern of both velocity and strain rate was remarkably consistent and must therefore be controlled by spatially fixed processes operating at the glacier bed. We combine these results with those published in the literature to construct a typical Svalbard glacier surge cycle and compare this to surge dynamics of glaciers from other cluster regions, especially those of Variegated Glacier in Alaska. The strong contrast in dynamics suggests that there exist at least two distinct surge mechanisms. Sherpa Romeo green journal. Permission to archive final published version.

Late surge glacial conditions on Bakaninbreen, Svalbard, and implications for surge termination Smith, A. M.; Murray, Tavi; Davison, B. M.; Clough, A. F.; Woodward, J.; Jiskoot, Hester Bakaninbreen is a polythermal glacier in southern Spitsbergen, Svalbard, that last surged between 1985 and 1995. Seismic reflection data were acquired during early quiescence in spring 1998, just upstream of the surge front. The results were combined with complementary ground-penetrating radar data to investigate the glacial structure and basal conditions. We find no difference between the ice thickness values determined from the seismic and radar methods, suggesting that any layer of basal ice cannot be greater than 5 m thick. Interpretation of the amplitude of the seismic reflections indicates the presence of permafrost close to the glacier base. A thin layer of thawed deforming sediment separates the glacier from this underlying permafrost. In an area just upstream of the surge front the permafrost becomes discontinuous and may even be absent, the ice being underlain by 10–15 m of thawed sediments overlying deeper bedrock. Highpressure water is believed to have been required to maintain the propagation of the surge, and this area of thawed sediment is interpreted as a route for that water to escape from the basal system. When the surge front passed over this thawed bed, the escaping water reduced the pressure in the subglacial hydraulic system, initiating the termination of the surge. Surge termination was therefore primarily controlled by the presurge permafrost distribution beneath the glacier, rather than any feature of the surge itself. This termination mechanism is probably limited to surges in polythermal glaciers, but the techniques used may have wider glaciological applications. Sherpa Romeo green journal. Permission to archive final published version

Glacier surge propagation by thermal evolution at the bed Murray, Tavi; Stuart, Graham W.; Miller, Paul J.; Woodward, John; Smith, Andrew M.; Porter, Philip R.; Jiskoot, Hester Bakaninbreen, southern Svalbard, began a prolonged surge during 1985. In 1986, an internal reflecting horizon on radio echo sounding data was interpreted to show that the position of the surge front coincided with a transition between areas of warm (unfrozen) and cold (frozen) bed. Ground-penetrating radar lines run in 1996 and 1998 during early quiescence show that the basal region of the glacier is characterized by a strong reflection, interpreted as the top of a thick layer of sediment-rich basal ice. Down glacier of the present surge front, features imaged beneath the basal reflection are interpreted as the bottom of the basal ice layer, the base of a permafrost layer, and local ice lenses. This indicates that this region of the bed is cold. Up glacier of the surge front, a scattering zone above the basal reflection is interpreted as warm ice. There is no evidence for this warm zone down glacier of the surge front, nor do we see basal permafrost up glacier of it. Thus, as in early surge phase, the location of the surge front is now at the transition between warm and cold ice at the glacier bed. We suggest that the propagation of the front is associated with this basal thermal transition throughout the surge. Because propagation of the front occurs rapidly and generates only limited heat, basal motion during fast flow must have been restricted to a thin layer at the bed and occurred by sliding or deformation localized at the ice-bed interface. Sherpa Romeo green journal. Permission to archive final published version.

Multiple tropical Andean glaciations during a period of late Pliocene warmth Roberts, Nicholas J.; Barendregt, René W.; Clague, John J. The extent and behaviour of glaciers during the mid-Piacenzian warm period illustrate the sensitivity of the cryosphere to atmospheric CO2 concentrations above pre-industrial levels. Knowledge of glaciation during this period is restricted to globally or regionally averaged records from marine sediments and to sparse terrestrial glacial deposits in mid-to-high latitudes. Here we expand the Pliocene glacial record to the tropics by reporting recurrent large-scale glaciation in the Bolivian Andes based on stratigraphic and paleomagnetic analysis of a 95-m sequence of glacial sediments underlying the 2.74-Ma Chijini Tuff. Paleosols and polarity reversals separate eight glacial diamictons, which we link to cold periods in the benthic oxygen isotope record. The glaciations appear to coincide with the earliest glacial activity at high northern latitudes and with events in Antarctica, including the strong M2 cold peak and terminal Pliocene climate deterioration. This concordance suggests inter-hemispheric climate linkages during the late Pliocene and requires that the Central Andes were at least as high in the late Pliocene as today. Our record fills a critical gap in knowledge of Earth systems during the globally warm mid-Piacenzian and suggests a possible driver of faunal migration preceding the large-scale biotic interchange in the Americas during the earliest Pleistocene. Sherpa Romeo green journal. Open access article. Creative Commons Attribution 4.0 International License (CC by 4.0) applies

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Questions remain about the safety and effectiveness of alternative solvents

Es necesario un cambio cultural para evitar seguir perjudicando a las investigadoras

Although some kinks are still being worked out, the European XFEL is now giving researchers an unprecedented view of the inner workings of molecules and materials

Rising CO₂ levels could stop fish finding food and detecting predators

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