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A new calving algorithm is developed in the glacier model Elmer/Ice that allows unrestricted calving and terminus advance in 3D. The algorithm uses the meshing software Mmg to implement anisotropic remeshing and allow mesh adaptation at each time step. The development of the algorithm, along with the implementation of the crevasse depth law, produces a new full-Stokes calving model capable of simulating calving and terminus advance across an array of complex geometries. Using a synthetic tidewater glacier geometry, the model is tested to highlight the numerical model parameters that can alter calving when using the crevasse depth law. For a system with no clear attractor at a pinning point, the model time step and mesh resolution are shown to alter the simulated calving. In particular, the vertical mesh resolution has a large impact, increasing calving, as the frontal bending stresses are better resolved. However, when the system has a strong attractor, provided by basal pinning points, numerical model parameters have a limited effect on the terminus evolution. Conversely, transient systems with no clear attractors are highly influenced by the choice of numerical model parameters. The new algorithm is capable of implementing unlimited terminus advance and retreat, as well as unrestricted calving geometries, applying any vertically varying melt distribution to the front for use in conjunction with any calving law or potentially advecting variables downstream. In overcoming previous technical hurdles, the algorithm opens up the opportunity to improve both our understanding of the physical processes and our ability to predict calving. [ABSTRACT FROM AUTHOR]

We investigate the physical basis of the crevasse-depth (CD) calving law by analysing relationships between glaciological stresses and calving behaviour at Sermeq Kujalleq (Store Glacier), Greenland. Our observations and model simulations show that the glacier has a stable position defined by a compressive arch between lateral pinning points. Ice advance beyond the arch results in calving back to the stable position; conversely, if melt-undercutting forces the ice front behind the stable position, it readvances because ice velocities exceed subaqueous melt rates. This behaviour is typical of self-organising criticality, in which the stable ice-front position acts as an attractor between unstable super-critical and sub-critical regimes. This perspective provides strong support for a 'position-law' approach to modelling calving at Sermeq Kujalleq, because any calving 'rate' is simply a by-product of how quickly ice is delivered to the critical point. The CD calving law predicts ice-front position from the penetration of surface and basal crevasse fields, and accurately simulates super-critical calving back to the compressive arch and melt-driven calving into the sub-critical zone. The CD calving law reflects the glaciological controls on calving at Sermeq Kujalleq and exhibits considerable skill in simulating its mean position and seasonal fluctuations. [ABSTRACT FROM AUTHOR]

We present the first fully coupled 3D full-Stokes model of a tidewater glacier, incorporating ice flow, subglacial hydrology, plume-induced frontal melting and calving. We apply the model to Store Glacier (Sermeq Kujalleq) in west Greenland to simulate a year of high melt (2012) and one of low melt (2017). In terms of modelled hydrology, we find perennial channels extending 5 km inland from the terminus and up to 41 and 29 km inland in summer 2012 and 2017, respectively. We also report a hydrodynamic feedback that suppresses channel growth under thicker ice inland and allows water to be stored in the distributed system. At the terminus, we find hydrodynamic feedbacks exert a major control on calving through their impact on velocity. We show that 2012 marked a year in which Store Glacier developed a fully channelised drainage system, unlike 2017, where it remained only partially developed. This contrast in modelled behaviour indicates that tidewater glaciers can experience a strong hydrological, as well as oceanic, control, which is consistent with observations showing glaciers switching between types of behaviour. The fully coupled nature of the model allows us to demonstrate the likely lack of any hydrological or ice-dynamic memory at Store Glacier. [ABSTRACT FROM AUTHOR]

The response of tidewater glaciers to ocean warming remains a key uncertainty in sea level rise predictions. Here we use a 3‐D numerical model to examine the response of an idealized tidewater glacier to spatial variations in submarine melt rate. While melting toward the center of the terminus causes only a localized increase in mass loss, melting near the lateral margins triggers increased calving across the width of the glacier, causing the terminus to retreat at several times the width‐averaged melt rate. This occurs because melting near the margins has a greater disruptive impact on the compressive stress arch that transfers resistance from the side walls to the body of the glacier. We suggest that the rate of terminus advance or retreat may thus be governed by the difference between ice velocity and submarine melting in the slow‐flowing zones away from the glacier center. Plain Language Summary: The rapid retreat of tidewater glaciers (i.e., glaciers that drain directly into the ocean) has become an increasing source of concern in recent years. Increased melting of the submerged parts of these glaciers by warming ocean waters is thought to be an important driver of this retreat, but exactly how glaciers respond to this submarine melting remains unclear. Using a numerical model, we find that tidewater glaciers may be most sensitive to melting close to the valleysides, which reduces structural support for the central section of the glacier and so triggers an increase in iceberg calving. By better constraining the relationships between submarine melting, calving, and glacier retreat, our findings allow improved prediction of the ice loss expected from tidewater glaciers as the climate continues to warm. Key Points: We use a 3‐D numerical model to examine the response of an idealized tidewater glacier to spatial variations in submarine melt rateThe glacier is most sensitive to melting near the lateral margins, which triggers increased calving across the width of the terminusTerminus retreat may thus be paced by the difference between ice velocity and submarine melting across slow flowing marginal zones [ABSTRACT FROM AUTHOR]

The ongoing retreat of many tidewater glaciers has been attributed to the increased submarine melting of calving fronts in response to warming oceans and increased meltwater runoff. The mechanisms through which submarine melting affects the stability of tidewater glaciers remain poorly understood however. In particular, the existence of a 'calving amplifier effect', in which submarine melting leads to a further increase in ice loss through calving, remains uncertain. Numerical modelling experiments have shown that this effect may occur when a glacier calving front is undercut due to vertical variation in the rate of submarine melting. There has however been relatively little investigation of the impact on calving, and thus total mass loss, of lateral variation in melting across the calving front.Here, we use a three-dimensional, full-Stokes glacier calving model implemented in Elmer/Ice to examine the response of an idealised tidewater glacier to spatially variable submarine melting. The model uses a crevasse-depth calving criterion that triggers calving when surface and basal crevasses penetrate the full thickness of the glacier. We subject the model glacier to spatially discrete areas of submarine melting representing the zones of intense localised melting that occur at tidewater glaciers where the input of subglacial runoff drives vigorous plumes adjacent to the calving front. We find that submarine melting may have both a positive and a negative impact on the calving rate, depending on a range of variables including the intensity of the melting, the extent of the calving front subject to melting, and location of these zones of intense melting along the calving front. In particular, we find that the greatest positive impact on calving occurs when submarine melting is applied close to the ice margins rather than in the centre of the glacier. This occurs because as the melting incises notches into the calving front, it disrupts the natural compressive stress-arch that provides support to the centre of the glacier, isolating it from the stabilising influence of the fjord walls and thus triggering calving until a new stable geometry is formed. It is thus possible that through this calving amplifier effect, small areas of intense plume-driven melting could trigger enhanced calving and retreat even at large and fast-flowing glaciers at which the average submarine melt rate remains below the glacier velocity. [ABSTRACT FROM AUTHOR]