Supraglacial forcing of subglacial drainage in the ablation zone of the Greenland ice sheet

Peer reviewedPublisher PD

Short-term variability in Greenland Ice Sheet motion forced by time-varying meltwater inputs: implications for the relationship between subglacial drainage system behavior and ice velocity.

High resolution measurements of ice motion along a -120 km transect in a land-terminating section of the GrIS reveal short-term velocity variations (<1 day), which are forced by rapid variations in meltwater input to the subglacial drainage system from the ice sheet surface. The seasonal changes in ice velocity at low elevations (<1000 m) are dominated by events lasting from 1 day to 1 week, although daily cycles are largely absent at higher elevations, reflecting different patterns of meltwater input. Using a simple model of subglacial conduit behavior we show that the seasonal record of ice velocity can be understood in terms of a time-varying water input to a channelized subglacial drainage system. Our investigation substantiates arguments that variability in the duration and rate, rather than absolute volume, of meltwater delivery to the subglacial drainage system are important controls on seasonal patterns of subglacial water pressure, and therefore ice velocity. We suggest that interpretations of hydro-dynamic behavior in land-terminating sections of the GrIS margin which rely on steady state drainage theories are unsuitable for making predictions about the effect of increased summer ablation on future rates of ice motion. © 2012. American Geophysical Union

Variability in ice motion at a land-terminating Greenlandic outlet glacier: the role of channelized and distributed drainage systems

We use a combination of field observations and hydrological modelling to examine the mechanisms through which variability in meltwater input affects ice motion at a land-terminating Greenlandic outlet glacier. We find a close agreement between horizontal ice velocity, vertical ice velocity and modelled subglacial water pressure over the course of a melt season. On this basis, we argue that variation in horizontal and vertical ice velocity primarily reflects the displacement of basal ice during periods of cavity expansion and contraction, a process itself driven by fluctuations in basal water pressure originating in subglacial channels. This process is not captured by traditional sliding laws linking water pressure and basal velocity, which may hinder the simulation of realistic diurnal to seasonal variability in ice velocity in coupled models of glacial hydrology and dynamics

Hydrology and dynamics of a land-terminating Greenland outlet glacier

The purpose of this thesis is to investigate the hydrology and dynamics of a land-terminating outlet glacier on the western margin of the Greenland Ice Sheet (GrIS). The investigations are motivated by uncertainty about the effect of meltwater on rates of ice flow in the GrIS and the possibility that hydrologically forced changes in ice velocity might increase mass loss from the ice sheet significantly in response to climate warming. The impact of meltwater on fluctuations in ice flow has been a research focus for glaciologists studying Alpine and Arctic glaciers for decades. In these settings, one of the main controls on the relationship between surface melting and ice velocity is the structure of the subglacial drainage system, which evolves spatially and temporally on a seasonal basis in response to inputs of meltwater from the glacier surface. In this thesis we present three years of field observations of glacier velocity, surface ablation and hydrology from a land-terminating glacier in west Greenland. These data are supplemented by satellite data and the use of simple models to constrain surface melting. We find that hydrologically forced ice acceleration occurs each year along a 115 km transect, first at sites nearest the ice sheet margin and at locations further inland following the onset of surface melting at higher elevations. At sites near the ice sheet margin, the relationship between surface melting and ice velocity is not consistent throughout the melt season, and ice velocity becomes less sensitive to inputs of meltwater later in the summer. This is explained by development in the efficiency of the subglacial drainage system, in a manner similar to Alpine glaciers. We perform a hydrological study which indicates that an efficient subglacial drainage system expands upglacier over the course of the melt season, in response to inputs of water from the ice sheet surface. At higher elevation sites, however, thicker ice and colder temperatures mean that it is harder to generate enough water to reach the ice-bed interface and this only occurs once enough water has accumulated to propagate fractures through thick ice to the bed. One mechanism which allows this is drainage of supraglacial lakes. Inter-annual comparison shows that increased rates of annual ablation lead to higher annual ice velocities. At high elevation sites (>1000 m), timing of drainage of meltwater to the ice-bed interface appears to be the main control on the the overall magnitude of summer acceleration. At lower elevations, although development in the structure of the subglacial drainage system limits the overall summer acceleration signal, short-term variability in meltwater input can sustain high ice velocities even once the subglacial drainage system has become channelised. Overall, the research presented in this thesis suggests that hydrologically-forced acceleration can increase mass loss from the GrIS in a warmer climate due to inland expansion of the area of the ice sheet bed which is subject to inputs of meltwater from the ice sheet surface. The relationship between surface melting and ice velocity is mediated, however, by the structure of the subglacial drainage system and variations in the rate of meltwater drainage to the ice bed interface. Insights from this work can help in the development of numerical ice sheet models which aim to predict the future contribution to sea-level rise from the Greenland Ice Sheet

Development of a peer support intervention to encourage dietary behaviour change towards a Mediterranean diet in adults at high cardiovascular risk.

BACKGROUND: Mediterranean diet (MD) interventions are demonstrated to significantly reduce cardiovascular disease (CVD) risk but are typically resource intensive and delivered by health professionals. There is considerable interest to develop interventions that target sustained dietary behaviour change and that are feasible to scale-up for wider public health benefit. The aim of this paper is to describe the process used to develop a peer support intervention to encourage dietary behaviour change towards a MD in non-Mediterranean adults at high CVD risk. METHODS: The Medical Research Council (MRC) and Behaviour Change Wheel (BCW) frameworks and the COM-B (Capability, Opportunity, Motivation, Behaviour) theoretical model were used to guide the intervention development process. We used a combination of evidence synthesis and qualitative research with the target population, health professionals, and community health personnel to develop the intervention over three main stages: (1) we identified the evidence base and selected dietary behaviours that needed to change, (2) we developed a theoretical basis for how the intervention might encourage behaviour change towards a MD and selected intervention functions that could drive the desired MD behaviour change, and (3) we defined the intervention content and modelled outcomes. RESULTS: A theory-based, culturally tailored, peer support intervention was developed to specifically target behaviour change towards a MD in the target population. The intervention was a group-based program delivered by trained peer volunteers over 12-months, and incorporated strategies to enhance social support, self-efficacy, problem-solving, knowledge, and attitudes to address identified barriers to adopting a MD from the COM-B analysis. CONCLUSIONS: The MRC and BCW frameworks provided a systematic and complementary process for development of a theory-based peer support intervention to encourage dietary behaviour change towards a MD in non-Mediterranean adults at high CVD risk. The next step is to evaluate feasibility, acceptability, and diet behaviour change outcomes in response to the peer support intervention (change towards a MD and nutrient biomarkers) using a randomized controlled trial design

A live weight-heart girth relationship for accurate dosing of east African shorthorn zebu cattle

The accurate estimation of livestock weights is important for many aspects of livestock management including nutrition, production and appropriate dosing of pharmaceuticals. Subtherapeutic dosing has been shown to accelerate pathogen resistance which can have subsequent widespread impacts. There are a number of published models for the prediction of live weight from morphometric measurements of cattle, but many of these models use measurements difficult to gather and include complicated age, size and gender stratification. In this paper, we use data from the Infectious Diseases of East Africa calf cohort study and additional data collected at local markets in western Kenya to develop a simple model based on heart girth circumference to predict live weight of east African shorthorn zebu (SHZ) cattle. SHZ cattle are widespread throughout eastern and southern Africa and are economically important multipurpose animals. We demonstrate model accuracy by splitting the data into training and validation subsets and comparing fitted and predicted values. The final model is weight0.262 =0.95 + 0.022 × girth which has an R2 value of 0.98 and 95 % prediction intervals that fall within the ±20 % body weight error band regarded as acceptable when dosing livestock. This model provides a highly reliable and accurate method for predicting weights of SHZ cattle using a single heart girth measurement which can be easily obtained with a tape measure in the field setting

Identification of two novel powdery mildew resistance loci, Ren6 and Ren7, from the wild Chinese grape species Vitis piasezkii

Descriptive statistics of the phenotypic scores within the base mapping population 11-373. Powdery mildew symptoms in the field were evaluated in two subsequent years. Greenhouse, in vitro experiments and the qPCR-based molecular assay were carried out with three to four biological replicates of each seedling plant in 2014. (DOCX 14ย�kb