Calving on tidewater glaciers amplified by submarine frontal melting

While it has been shown repeatedly that ocean conditions exhibit an important control on the behaviour of grounded tidewater glaciers, modelling studies have focused largely on the effects of basal and surface melting. Here, a finite-element model of stresses near the front of a tidewater glacier is used to investigate the effects of frontal melting on calving, independently of the calving criterion used. Applications of the stress model to idealized scenarios reveal that undercutting of the ice front due to frontal melting can drive calving at up to ten times the mean melt rate. Factors which cause increased frontal melt-driven calving include a strong thermal gradient in the ice, and a concentration of frontal melt at the base of the glacier. These properties are typical of both Arctic and Antarctic tidewater glaciers. The finding that frontal melt near the base is a strong driver of calving leads to the conclusion that water temperatures near the bed of the glacier are critically important to the glacier front, and thus the flow of the glacier. These conclusions are robust against changes in the basal boundary condition and the choice of calving criterion, as well as variations in the glacier size or level of crevassing

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Fælles udenrigstjeneste med fødselsvanskeligheder

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Calving on tidewater glaciers amplified by submarine frontal melting

While it has been shown repeatedly that ocean conditions exhibit an important control on the behaviour of grounded tidewater glaciers, modelling studies have focused largely on the effects of basal and surface melting. Here, a finite-element model of stresses near the front of a tidewater glacier is used to investigate the effects of frontal melting on calving, independently of the calving criterion used. Applications of the stress model to idealized scenarios reveal that undercutting of the ice front due to frontal melting can drive calving at up to ten times the mean melt rate. Factors which cause increased frontal melt-driven calving include a strong thermal gradient in the ice, and a concentration of frontal melt at the base of the glacier. These properties are typical of both Arctic and Antarctic tidewater glaciers. The finding that frontal melt near the base is a strong driver of calving leads to the conclusion that water temperatures near the bed of the glacier are critically important to the glacier front, and thus the flow of the glacier. These conclusions are robust against changes in the basal boundary condition and the choice of calving criterion, as well as variations in the glacier size or level of crevassing

Sensitivity of calving glaciers to ice-ocean interactions under climate change: New insights from a 3D full-Stokes model

Iceberg calving accounts for between 30% and 60% of net mass loss from the Greenland Ice Sheet, which has intensified and is now the single largest contributor to global sea level rise in the cryosphere. Changes to calving rates and the dynamics of calving glaciers represent a significant uncertainty in projections of future sea level rise. A growing body of observational evidence suggests that calving glaciers respond rapidly to regional environmental change, but predictive capacity is limited by the lack of suitable models capable of simulating calving mechanisms realistically. Here, we use a 3-D full-Stokes calving model to investigate the environmental sensitivity of Store Glacier, a large outlet glacier inWest Greenland.We focus on two environmental processes: undercutting by submarine melting and buttressing by ice mélange, and our results indicate that Store Glacier is likely to be able to withstand moderate warming perturbations in which the former is increased by 50% and the latter reduced by 50 %. However, severe perturbation with a doubling of submarine melt rates or a complete loss of ice mélange destabilises the calving front in our model runs. Furthermore, our analysis reveals that stress and fracture patterns at Store’s terminus are complex and varied, primarily due to the influence of basal topography. Calving style and environmental sensitivity vary greatly, with propagation of surface crevasses significantly influencing iceberg production in the northern side, whereas basal crevasses dominate in the south. Any future retreat is likely to be initiated in the southern side by a combination of increased submarine melt rates in summer and reduced mélange strength in winter. The lateral variability, as well as the importance of rotational and bending forces at the terminus, underlines the importance of using the 3-D full-Stokes stress solution when modelling Greenland’s calving glaciers.Article is output from NERC PhD studentship (Todd) and NERC grant (Christoffersen

Cascading lake drainage on the Greenland Ice Sheet triggered by tensile shock and fracture

Supraglacial lakes on the Greenland Ice Sheet are expanding inland, but the impact on ice flow is equivocal because interior surface conditions may preclude the transfer of surface water to the bed. Here we use a well-constrained 3D model to demonstrate that supraglacial lakes in Greenland drain when tensile-stress perturbations propagate fractures in areas where fractures are normally absent or closed. These melt-induced perturbations escalate when lakes as far as 80?km apart form expansive networks and drain in rapid succession. The result is a tensile shock that establishes new surface-to-bed hydraulic pathways in areas where crevasses transiently open. We show evidence for open crevasses 135?km inland from the ice margin, which is much farther inland than previously considered possible. We hypothesise that inland expansion of lakes will deliver water and heat to isolated regions of the ice sheet?s interior where the impact on ice flow is potentially largepublishersversionPeer reviewe

Про ефективність діяльності товарних бірж України в роки НЕПу

Об’єктом дослідження статті є економічна та соціальна ефективність діяльності товарних бірж України в період непу. При цьому основна увага зосереджується на таких аспектах проблеми: посередництво в купівлі й продажу товарів; реєстрація позабіржових угод; надання послуг учасникам біржового торгу; підтримка комерційної освіти, благодійність тощо.Объектом исследования статьи является экономическая и социальная эффективность деятельности товарных бирж Украины в период нэпа. При этом основное внимание сосредоточивается на таких аспектах проблемы: посредничество в купле и продаже товаров; регистрация внебиржевых сделок; предоставление услуг участникам биржевого торга; поддержка коммерческого образования, благотворительность и т. п

Sensitive response of the Greenland Ice Sheet to surface melt drainage over a soft bed

This is the accepted manuscript. The final version is available from Nature Communications at http://www.nature.com/ncomms/2014/140929/ncomms6052/full/ncomms6052.html.The dynamic response of the Greenland Ice Sheet (GrIS) depends on feedbacks between surface meltwater delivery to the subglacial environment and ice flow. Recent work has highlighted an important role of hydrological processes in regulating the ice flow, but models have so far overlooked the mechanical effect of soft basal sediment. Here we use a three-dimensional model to investigate hydrological controls on a GrIS soft-bedded region. Our results demonstrate that weakening and strengthening of subglacial sediment, associated with the seasonal delivery of surface meltwater to the bed, modulates ice flow consistent with observations. We propose that sedimentary control on ice flow is a viable alternative to existing models of evolving hydrological systems, and find a strong link between the annual flow stability, and the frequency of high meltwater discharge events. Consequently, the observed GrIS resilience to enhanced melt could be compromised if runoff variability increases further with future climate warming.RCU