Elmer/Ice News

Calving forensics in Northwest Greenland

This article highlights the influence of surface meltwater and tides on crevasse opening leaEefDongen Bowdoin ElmerIceWebding to major calving events at grounded tidewater glaciers, such as Bowdoin Glacier, Northwest Greenland, where most calving occurs by a few large events resulting from kilometre-scale fractures forming parallel to the calving front. High-resolution terrestrial radar interferometry data of such an event reveal that crevasse opening is fastest at low tide and accelerates during the final 36 h before calving. Using  Elmer/Ice, the authors identify the crevasse water level as a key driver of modelled opening rates. Sea water-level variations in the range of local tidal amplitude (1 m) can reproduce observed opening rate fluctuations, provided crevasse water level is at least 4 m above the low-tide sea level. The accelerated opening rates within the final 36 h before calving can be modelled by additional meltwater input into the crevasse, enhanced ice cliff undercutting by submarine melt, ice damage increase due to tidal cyclic fatigue, crevasse deepening or a combination of all these processes.

Read more: van Dongen E.,G. Jouvet,A. Walter,J. Todd,T. Zwinger,I. Asaji,S. Sugiyama, F. Walter and M. Funk, 2019. Tides modulate crevasse opening prior to a major calving event at Bowdoin Glacier, Northwest Greenland. Journal of Glaciology 1–11, DOI: 10.1017/jog.2019.89.

Elmer/Ice used for the interpretation of millennial-scale ice cores drilled at Colle Gnifetti

liciulli2019The high-Alpine ice-core drilling site Colle Gnifetti (CG), Monte Rosa, Swiss/Italian Alps, provides climate records over the last millennium and beyond. However, the full exploitation of the oldest part of the existing ice cores requires complementary knowledge of the intricate glacio-meteorological settings, including glacier dynamics. Here, we present new ice-flow modeling studies of CG, focused on characterizing the flow at two neighboring drill sites in the eastern part of the glacier. The 3-D full Stokes ice-flow model is implemented using the finite element software Elmer/Ice and is thermo-mechanically coupled, includes firn rheology, firn densification and enthalpy transport. Measurements of surface velocities, accumulation, borehole inclination, density and englacial temperatures are used to validate the model output. We calculate backward trajectories using the Runge–Kutta integrator implemented in ParaView and map the core catchment areas. This constrains, for the first time at this site, the so-called upstream effects for the stable water isotope time series of the two ice cores drilled in 2005 and 2013. The model also provides a 3-D age field of the glacier and independent ice-core chronologies for five ice-core sites. Considering the ice core recovered in 2013, the model predicts a near-to-basal age of ~3000 years, which is consistent with radiocarbon dating results. Model results are a valuable addition to the existing glaciological and ice-core datasets. This especially concerns the quantitative estimate of upstream conditions affecting the interpretation of the deep ice-core layers.

Read more: Licciulli C, P. Bohleber, J. Lier, O. Gagliardini, M. Hoelzle and O. Eisen, 2019. A fullStokes ice-flow model to assist theinterpretation of millennial-scale ice cores atthe high-Alpine drilling site Colle Gnifetti, Swiss/Italian Alps. Journal of Glaciology 1-14, DOI: 10.1017/jog.2019.82.

Kinematic response of ice-rise divides to changes in ocean and atmosphere forcing

Fig2 DivArchSketchFinalThe majority of Antarctic ice shelves are bounded by grounded ice rises. These ice rises exhibit local flow fields that partially oppose the flow of the surrounding ice shelves. Formation of ice rises is accompanied by a characteristic upward-arching internal stratigraphy (“Raymond arches”), whose geometry can be analysed to infer information about past ice-sheet changes in areas where other archives such as rock outcrops are missing. Here we present an improved modelling framework using Elmer/Ice to study ice-rise evolution using a satellite-velocity calibrated, isothermal, and isotropic 3-D full-Stokes model including grounding-line dynamics at the required mesh resolution (<500 m). This overcomes limitations of previous studies where ice-rise modelling has been restricted to 2-D and excluded the coupling between the ice shelf and ice rise. We apply the model to the Ekström Ice Shelf, Antarctica, containing two ice rises. Our simulations investigate the effect of surface mass balance and ocean perturbations onto ice-rise divide position and interpret possible resulting unique Raymond arch geometries. Our perturbation simulations for the Ekström catchment reveal that SMB perturbations result in fast divide migration (up to 3.5 m /a), while shelf thickness perturbations only trigger slow divide migration (< 0.75 m /a). The amplitude of divide migration is predominately controlled by the subglacial topography and SMB, with ice-shelf buttressing being of secondary importance. We also track the migration of a triple junction and synchronous ice-divide migration in both ice rises with similar magnitude but differing rates. The model is suitable for glacial/interglacial simulations on the catchment scale, providing the next step forward to unravel the ice-dynamic history stored in ice rises all around Antarctica.

Read more: Schannwell C., R. Drews, T.A. Ehlers, O. Eisen, C. Mayer and F. Gillet-Chaulet, 2019. Kinematic response of ice-rise divides to changes in ocean and atmosphere forcing, The Cryosphere, 13, 2673–2691, DOI: 10.5194/tc-13-2673-2019.

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