Lacustrine ice-margin dynamics in west Greenland

There has been a progressive increase in the number and area of ice-marginal lakes along the western margin of the Greenland Ice Sheet (GrIS) since the late 1980s. Ice-marginal lake formation and growth have been widely associated with accelerated rates of mass loss and terminus recession at alpine glaciers, yet their impacts on the GrIS have remained unquantified. This thesis therefore investigated the influence of ice-marginal lakes on ice-margin dynamics in west Greenland at multiple spatial and temporal scales, using both established remote sensing techniques and the novel integration of time-lapse photography with Structure-from-Motion and Multi-View Stereo. A regional-decadal scale analysis of ice-margin change along a ~5000 km length of the GrIS revealed that lake-terminating ice-margins receded faster than their terrestrial counterparts between 1987 and 2015. In addition, the rate of recession at lake-terminating ice-margins accelerated over the study period and increasingly outpaced recession at terrestrial ice-margins. Altitude, latitude, lake area and the length of the lake – ice-margin interface were also identified as significant controls on rates of lake-terminating ice-margin recession. Local-seasonal scale ice-margin dynamics were investigated using the first continuous year-round volumetric record of calving at a lacustrine ice-margin. These data highlighted two distinct calving regimes; with melt-undercutting driving high calving rates under ice-free lake conditions, and force imbalances at the ice-cliff driving low calving rates when the lake was frozen. These results are important because they demonstrate that ice-marginal lakes are key regulators of ice-margin dynamics at the GrIS. The quantitative data derived through this study provide an empirical foundation upon which modelling efforts can incorporate the influence of ice-marginal processes. This is particularly pertinent given that rates of mass loss and recession at lake-terminating margins of the GrIS are likely to accelerate in coming decades in response to continued ice-marginal lake expansion and a lengthening melt season

Calving Seasonality Associated With Melt-Undercutting and Lake Ice Cover

A detailed understanding of calving processes at the lacustrine margins of the Greenland ice sheet is necessary for accurately forecasting its dynamic response to ongoing climate change. However, existing data sets of lacustrine calving are limited to summer seasons and to alpine glaciers. Here, we use an integrated time‐lapse and structure‐from‐motion approach to generate the first continuous year‐round volumetric record of calving processes at a lacustrine ice sheet margin. We identify two distinct calving regimes that are associated with melt‐undercutting and lake ice cover. We also find that calving rates respond rapidly to sudden lake drainage. Given that lake temperature, lake ice cover, and sudden lake drainages are controlled by air temperature and ice‐margin thinning, we suggest that climate change, manifested in lengthening summer seasons, will accelerate rates of mass loss and terminus recession at lacustrine ice‐margins in Greenland

An integrated Structure-from-Motion and time-lapse technique for quantifying ice-margin dynamics

Fine resolution topographic data derived from methods such as Structure from Motion (SfM) and Multi-View Stereo (MVS) have the potential to provide detailed observations of geomorphological change, but have thus far been limited by the logistical constraints of conducting repeat surveys in the field. Here, we present the results from an automated time-lapse camera array, deployed around an ice-marginal lake on the western margin of the Greenland ice sheet. Fifteen cameras acquired imagery three-times per day over a 426 day period, yielding a dataset of ~19 000 images. From these data we derived 18 point clouds of the ice-margin across a range of seasons and successfully identified calving events (ranging from 234 to 1475 m2 in area and 815–8725 m3 in volume) induced by ice cliff undercutting at the waterline and the collapse of spalling flakes. Low ambient light levels, locally reflective surfaces and the large survey range hindered analysis of smaller scale ice-margin dynamics. Nevertheless, this study demonstrates that an integrated SfM-MVS and time-lapse approach can be employed to generate long-term 3-D topographic datasets and thus quantify ice-margin dynamics at a fine spatio-temporal scale. This approach provides a template for future studies of geomorphological change

Ice-Dammed Lake Drainage Evolution at Russell Glacier, West Greenland

KEY POINTS/HIGHLIGHTSTwo rapid ice-dammed lake drainage events gauged and ice dam geometry measured.A melt enlargement model is developed to examine the evolution of drainage mechanism(s).Lake temperature dominated conduit melt enlargement and we hypothesize a flotation trigger.Glaciological and hydraulic factors that control the timing and mechanisms of glacier lake outburst floods (GLOFs) remain poorly understood. This study used measurements of lake level at 15 min intervals and known lake bathymetry to calculate lake outflow during two GLOF events from the northern margin of Russell Glacier, west Greenland. We used measured ice surface elevation, interpolated subglacial topography and likely conduit geometry to inform a melt enlargement model of the outburst evolution. The model was tuned to best-fit the hydrograph rising limb and timing of peak discharge in both events; it achieved Mean Absolute Errors of <5%. About one third of the way through the rising limb, conduit melt enlargement became the dominant drainage mechanism. Lake water temperature, which strongly governed the enlargement rate, preconditioned the high peak discharge and short duration of these floods. We hypothesize that both GLOFs were triggered by ice dam flotation, and localized hydraulic jacking sustained most of their early-stage outflow, explaining the particularly rapid water egress in comparison to that recorded at other ice-marginal lakes. As ice overburden pressure relative to lake water hydraulic head diminished, flow became confined to a subglacial conduit. This study has emphasized the inter-play between ice dam thickness and lake level, drainage timing, lake water temperature and consequently rising stage lake outflow and flood evolution

Ice‐marginal proglacial lakes across Greenland: Present status and a possible future

Ice-marginal lakes can affect glacier dynamics but are ignored in studies of the evolution of the Greenland ice sheet (GrIS) and of peripheral mountain glaciers and ice caps (PGICs). Here we show that lakes occupy 10 % of the GrIS ice margin and occur on 5 % of PGICs. Ice velocity at the GrIS margin is enhanced by ∼ 25 % at lakes versus on land. Mean ice discharge into lakes is ∼ 4.9 Gt.yr, which is ∼1 % of ice discharged through marine termini. We locate thousands of subglacial overdeepenings within which 7,404 km2 of future lakes could form, all of which will be ice-marginal at some time. Future lakes in the west and east will be restricted to the margin of the GrIS and within alpine valleys, respectively. This status and possible future leads us to contend that lakes should be incorporated into projections of Greenland ice loss

Identification of RO4597014, a Glucokinase Activator Studied in the Clinic for the Treatment of Type 2 Diabetes

To resolve the metabolite redox cycling associated with our earlier clinical compound <b>2</b>, we carried out lead optimization of lead molecule <b>1</b>. Compound <b>4</b> showed improved lipophilic ligand efficiency and demonstrated robust glucose lowering in diet-induced obese mice without a liability in predictive preclinical drug safety studies. Thus, it was selected as a clinical candidate and further studied in type 2 diabetic patients. Clinical data suggests no evidence of metabolite cycling, which is consistent with the preclinical profiling of metabolism