Elastic deformation plays a non-negligible role in Greenland’s outlet glacier flow

Future projections of global mean sea level change are uncertain, partly because of our limited understanding of the dynamics of Greenland’s outlet glaciers. Here we study Nioghalvfjerdsbræ, an outlet glacier of the Northeast Greenland Ice Stream that holds 1.1 m sea-level equivalent of ice. We use GPS observations and numerical modelling to investigate the role of tides as well as the elastic contribution to glacier flow. We find that ocean tides alter the basal lubrication of the glacier up to 10 km inland of the grounding line, and that their influence is best described by a viscoelastic rather than a viscous model. Further inland, sliding is the dominant mechanism of fast glacier motion, and the ice flow induces persistent elastic strain. We conclude that elastic deformation plays a role in glacier flow, particularly in areas of steep topographic changes and fast ice velocities.

Evaluation of ICEYE Microsatellites Sensor for Surface Motion Detection—Jakobshavn Glacier Case Study

The marine-terminating glaciers are one of the biggest contributors to global sea-level rise. Research on this aspect of the effects of global climate change is developing nowadays in several directions. One of them is monitoring of glaciers movements, especially with satellite data. In addition to well-known analyzes based on radar data from available satellites, the possibility of studying glacier displacements from new sensors, the so-called microsatellites need to be studied. The main purpose of research was evaluation of the possibility of applying new high-resolution ICEYE radar data to observe glacier motion. Stripmap High mode were used to obtain velocities for the Jakobshavn glacier with an Offset-Tracking method. Obtained results were compared with displacements obtained from the Sentinel-1 data. The comparative analysis was performed on displacements in range and azimuth directions and for maximum velocity values. Moreover, correlation plots showed that in different parts of glaciers, a comparison of obtained velocities delivers different correlation coefficients (R2) in a range from 0.52 to 0.97. The analysis showed that the scale of movements is similar from both sensors. However, Sentinel-1 data present underestimation of velocities comparing to ICEYE data. The biggest deviations between results were observed around the maximum velocities, near the Kangia Ice Fjord Bay. In the analysis the amplitude information was used as well. This research presents that data from the ICEYE microsatellites can be successfully used for monitoring glacial areas and it allows for more precise observations of displacement velocity field.

Ice-marginal lake hydrology and the seasonal dynamical evolution of Kennicott Glacier, Alaska

Glacier basal motion is responsible for the majority of ice flux on fast-flowing glaciers, enables rapid changes in glacier motion and provides the means by which glaciers shape alpine landscapes. In an effort to enhance our understanding of basal motion, we investigate the evolution of glacier velocity and ice-marginal lake stage on Kennicott Glacier, Alaska, during the spring–summer transition, a time when subglacial drainage is undergoing rapid change. A complicated record of > 50 m fill-and-drain sequences on a hydraulically-connected ice-marginal lake likely reflects the punctuated establishment of efficient subglacial drainage as the melt season begins. The rate of change of lake stage generally correlates with diurnal velocity maxima, both in timing and magnitude. At the seasonal scale, the up-glacier progression of enhanced summer basal motion promotes uniformity of daily glacier velocity fluctuations throughout the 10 km study reach, and results in diurnal velocity patterns suggesting increasingly efficient meltwater delivery to and drainage from the subglacial channel system. Our findings suggest the potential of using an ice-marginal lake as a proxy for subglacial water pressure, and show how widespread basal motion affects bulk glacier behavior.

Future impact of the Harmony InSAR satellite mission on land ice monitoring

<p>Current InSAR satellite missions have proven to be a valuable tool to monitor land ice worldwide. Applications are monitoring of glacier motion, ice/snow characteristics, but also glacier and snow type extend. Because these satellites work under all weather and lighting conditions, these missions are especially valuable in polar regions.</p><p>However, almost all current systems are restricted to repeat-pass interferometry and a single viewing geometry, limiting their use for land ice applications.</p><p>Harmony, an Earth Explorer 10 candidate mission, will strongly improve the capabilities of InSAR data for monitoring of land ice worldwide. This constellation comprises of two satellites that will fly as companions of one of the Sentinel-1 satellites. Harmony will make single-pass interferometry possible, which will be used to create improved, high-resolution digital elevation models to monitor ice mass loss. Additionally, single-pass interferometry will also provide us more details on ice and snow characteristics. Finally, every scene will be viewed from different look angles, which can enhance current ice flow estimates and allows the generation of precise three-dimensional ice motion products over the ice sheets.</p><p>In this study we show the future capabilities of the Harmony for land ice monitoring using performance models. Where possible, these models are calibrated and compared with already available Sentinel-1 data. Capabilities of the Sentinel-1 satellites for the monitoring of year-round ice movements and ice/snow characteristics are illustrated by a number of case studies.</p>

Subglacial water pressure records from a fast-flowing outlet glacier in Greenland

<p>Glacier motion is resisted by basal traction that can be reduced significantly by pressurised water at the ice-bed interface. Few records of subglacial water pressure have been collected from fast-flowing, marine-terminating glaciers despite such glaciers accounting for approximately half of total ice discharge from the Greenland Ice Sheet.  The paucity of such measurements is due to the practical challenges in drilling and instrumenting boreholes to the bed, in areas that are often heavily-crevassed, through rapidly-deforming ice that ruptures sensor cables within weeks. Here, we present pressure records and drilling observations from two sites located 30 km from the calving front of Store Glacier in West Greenland, where ice flow averages ~600 m yr<sup>-1</sup>.  In 2018, boreholes were drilled 950 m to the bed near the margin of a large, rapidly-draining supraglacial lake. In 2019, multiple boreholes were drilled ~1030 m to the bed in the centre of the drained supraglacial lake, and in close proximity to a large, active moulin. All boreholes drained rapidly when they intersected or approached the ice-bed interface, which is commonly interpreted as indicating connection to an active subglacial drainage system. Neighbouring boreholes responded to the breakthrough of subsequent boreholes demonstrating hydrological or mechanical inter-connection over a distance of ~70 m. Differences in the time series of water pressure indicate that each borehole intersected a distinct component of the subglacial hydrological system. Boreholes located within 250 m of the moulin reveal clear diurnal cycles either in phase or anti-phase with moulin discharge. Pressure records from boreholes located on the lake margin, however, show smaller amplitude, and less distinct, diurnal cycles superimposed on longer-period (e.g. multiday) variability. We compare these datasets to those in the literature and investigate consistencies and inconsistencies with glacio-hydrological theory.</p>

Effects of undercutting and sliding on calving: a coupled approach applied to Kronebreen, Svalbard

In this paper, we study the effects of basal friction, sub-aqueous undercutting and glacier geometry on the calving process with six different models: a continuum-mechanical ice flow model (Elmer/Ice), a climatic mass balance model, a simple subglacial hydrology model, a plume model, an undercut model and a discrete particle model to investigate fracture dynamics (Helsinki Discrete Element Model, HiDEM). We also demonstrate the feasibility of reproducing the observed calving retreat at the front of Kronebreen, a tidewater glacier in Svalbard, during a melt season. Basal sliding and glacier motion is addressed using Elmer/Ice while calving is modelled by HiDEM. An hydrology model calculates subglacial drainage paths and indicates two main outlets at relatively different rates. Depending on the discharge, the plume model computes frontal melt rates, which are iteratively projected to the actual front of the glacier at subglacial discharge locations. This produces undercutting of different sizes, as melt is concentrated close to the surface for high discharge and is more diffuse for low discharge. By testing different configurations, we show that the geometry (frontal position and topography) controls the calving location while basal sliding controls the calving rate. Undercutting plays a key role in glacier retreat and is necessary to reproduce observed retreat in the vicinity of the discharge location.