Browsing by Subject "ice-sheet"
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Item Challenges to Understanding the Dynamic Response of Greenland's Marine Terminating Glaciers to Oceanic and Atmospheric Forcing(2013-08) Straneo, Fiammetta; Heimbach, Patrick; Sergienko, Olga; Hamilton, Gordon; Catania, Ginny; Griffies, Stephen; Hallberg, Robert; Jenkins, Adrian; Joughin, Ian; Motyka, Roman; Pfeffer, W. Tad; Price, Stephen F.; Rignot, Eric; Scambos, Ted; Truffer, Martin; Vieli, Andreas; Catania, GinnyThe recent retreat and speedup of outlet glaciers, as well as enhanced surface melting around the ice sheet margin, have increased Greenland's contribution to sea level rise to 0.6 +/- 0.1 mm yr(-1) and its discharge of freshwater into the North Atlantic. The widespread, near-synchronous glacier retreat, and its coincidence with a period of oceanic and atmospheric warming, suggests a common climate driver. Evidence points to the marine margins of these glaciers as the region from which changes propagated inland. Yet, the forcings and mechanisms behind these dynamic responses are poorly understood and are either missing or crudely parameterized in climate and ice sheet models. Resulting projected sea level rise contributions from Greenland by 2100 remain highly uncertain. This paper summarizes the current state of knowledge and highlights key physical aspects of Greenland's coupled ice sheet-ocean-atmosphere system. Three research thrusts are identified to yield fundamental insights into ice sheet, ocean, sea ice, and atmosphere interactions, their role in Earth's climate system, and probable trajectories of future changes: 1) focused process studies addressing critical glacier, ocean, atmosphere, and coupled dynamics; 2) sustained observations at key sites; and 3) inclusion of relevant dynamics in Earth system models. Understanding the dynamic response of Greenland's glaciers to climate forcing constitutes both a scientific and technological frontier, given the challenges of obtaining the appropriate measurements from the glaciers' marine termini and the complexity of the dynamics involved, including the coupling of the ocean, atmosphere, glacier, and sea ice systems. Interdisciplinary and international cooperation are crucial to making progress on this novel and complex problem.Item A Ten-Year Record of Supraglacial Lake Evolution and Rapid Drainage in West Greenland Using an Automated Processing Algorithm for Multispectral Imagery(2013-12) Morriss, B. F.; Hawley, R. L.; Chipman, J. W.; Andrews, L. C.; Catania, G. A.; Hoffman, M. J.; Luthi, M. P.; Neumann, T. A.; Andrews, L. C.; Catania, G. A.The rapid drainage of supraglacial lakes introduces large pulses of meltwater to the subglacial environment and creates moulins, surface-to-bed conduits for future melt. Introduction of water to the subglacial system has been shown to affect ice flow, and modeling suggests that variability in water supply and delivery to the subsurface play an important role in the development of the subglacial hydrologic system and its ability to enhance or mitigate ice flow. We developed a fully automated method for tracking meltwater and rapid drainages in large (>0.125 km(2)) perennial lakes and applied it to a 10 yr time series of ETM+ and MODIS imagery of an outlet glacier flow band in West Greenland. Results indicate interannual variability in maximum coverage and spatial evolution of total lake area. We identify 238 rapid drainage events, occurring most often at low (< 900 m) and middle (900-1200 m) elevations during periods of net filling or peak lake coverage. We observe a general progression of both lake filling and draining from lower to higher elevations but note that the timing of filling onset, peak coverage, and dissipation are also variable. Lake coverage is sensitive to air temperature, and warm years exhibit greater variability in both coverage evolution and rapid drainage. Mid-elevation drainages in 2011 coincide with large surface velocity increases at nearby GPS sites, though the relationships between ice-shed-scale dynamics and meltwater input are still unclear.