I recently completed my Ph.D. research under the supervision of Dr. Ian Howat (Glacier Dynamics Group, Byrd Polar Research Center). To date, my research has focused on understanding the controls of variability in tidewater glacier behavior in response to climate change using remote sensing and numerical ice flow modeling techniques. I am particularly interested in ice-ocean interactions that occur at the margins of the Greenland and Antarctic ice sheets, which have the potential to contribute significant volumes of melt water to the global oceans as a result of ice dynamics. My postdoctoral research will explore ice-ocean interactions at Helheim Glacier, East Greenland under the supervision of Dr. Gordon Hamilton (University of Maine, Climate Change Institute). In order to develop a better understanding of recent mass loss from the Greenland Ice Sheet, I constructed time series of ice discharge change for 178 marine-terminating outlet glaciers from 2000-2012 with help from my colleagues at The Ohio State University. These discharge time series were then compiled to create a record of ice sheet discharge change. A time series of annual surface mass balance change was obtained from the Regional Atmospheric Climate Model for the Greenland Ice Sheet (RACMO/GR). The surface mass balance and discharge time series were combined to create record of ice sheet mass change since 2000. We found that changes in ice sheet discharge were driven by increased discharge from a small number of large and fast-flowing outlet glaciers (50% of cumulative discharge change from 4 glaciers). Despite the observed increase in ice sheet discharge from ~462 Gt/yr in 2000 to ~547 Gt/yr in 2012, ice sheet mass loss since 2000 was primarily due to increased meltwater runoff. The discharge data used for the published analysis (article) can be found here. As part of my dissertation project, I also developed a depth-integrated, width-averaged numerical ice flow model that can be used to efficiently model ice flow for the channelized tidewater glaciers draining much of the Greenland Ice Sheet. Thus far, the model has been used to examine the influence of uncertainty in glacier shape (article) as well as ice rheology and basal sliding parameterizations (article) on predictions of future glacier behavior. I have found that variations in outlet width control both the magnitude and timing of grounding line retreat into a basal depression following the onset of a perturbation to the glacier stress balance. In particular, lowering the depression height within the uncertainty of current ice-penetrating radar observations can result in glaciers switching from stable (i.e., ice remains grounded on a marine shoal) to unstable (i.e., rapid retreat into a basal depression). Additionally, I found that a non-unique combination of ice rheology and basal sliding parameterizations can be used to reproduce similar steady-state thickness and speed profiles but that following the onset of a perturbation, the dynamic behavior varies with the parameter choice. Based on these results, I suggest that prognostic ice flow models are either accompanied by sensitivity studies that investigate the influence of geometry and parameter uncertainty on predictions of dynamic behavior or that these models are not used as precise predictors of future glacier behavior. The model that I developed to perform my sensitivity studies is open access and can be obtained by sending an email to ellyn.enderlin@gmail.com. The model is set-up to run a demonstration and is accompanied by a user guide that explains the model basics, the demonstration, and how to modify the model for application to real glacier systems. I have also calculated submarine melt rates beneath floating termini for 13 marine-terminating outlet glaciers in Greenland from 2000-2010 in order to develop a better understanding of variability in ocean forcing that may be triggering the observed changes in dynamics. Annual melt season submarine melt rates were calculated by differencing grounding line and front discharge obtained through satellite image analysis, assuming that mass loss between the grounding line and front is due to submarine melting after accounting for mass loss from surface melt. Although the data are spatially and temporally limited, there was no correlation between changes in dynamics and submarine melt rates during the study period. Melt rates varied widely between glaciers, but, on average, mass loss from submarine melting was approximately equal to mass loss from the calving of icebergs from the glacier termini (article). My future research on ice-ocean interactions will rely on collaborative research projects that focus on using in situ and satellite-derived data to estimate submarine melt rates and determine how variability in ocean conditions influences ice dynamics. |
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