TY - JOUR T1 - Rapid Submarine Melting Driven by Subglacial Discharge, LeConte Glacier, Alaska JF - Geophysical Research Letters Y1 - 2013 A1 - Roman J. Motyka A1 - Dryer, W. P. A1 - Jason M Amundson A1 - Martin Truffer A1 - Mark Fahnestock KW - frontal ablation KW - submarine melting KW - tidewater glaciers AB - We show that subglacial freshwater discharge is the principal process driving high rates of submarine melting at tidewater glaciers. This buoyant discharge draws in warm seawater, entraining it in a turbulent upwelling flow along the submarine face that melts glacier ice. To capture the effects of subglacial discharge on submarine melting, we conducted 4 days of hydrographic transects during late summer 2012 at LeConte Glacier, Alaska. A major rainstorm allowed us to document the influence of large changes in subglacial discharge. We found strong submarine melt fluxes that increased from 9.1 ± 1.0 to 16.8 ± 1.3 m d−1 (ice face equivalent frontal ablation) as a result of the rainstorm. With projected continued global warming and increased glacial runoff, our results highlight the direct impact that increases in subglacial discharge will have on tidewater outlet systems. These effects must be considered when modeling glacier response to future warming and increased runoff. VL - 40 UR - http://dx.doi.org/10.1002/grl.51011 ER - TY - JOUR T1 - On the seasonal freshwater stratification in the proximity of fast-flowing tidewater outlet glaciers in a sub-Arctic sill fjord JF - Journal of Geophysical Research: Oceans Y1 - 2013 A1 - Mortensen, J. A1 - Bendtsen, J. A1 - Roman J. Motyka A1 - Lennert, K. A1 - Martin Truffer A1 - Mark Fahnestock A1 - Rysgaard, S. KW - fjord KW - freshwater sources and their distribution KW - Greenland Ice Sheet KW - subglacial freshwater fraction model KW - subsurface heat sources for glacial ice melt KW - tidewater outlet glaciers AB - The Greenland Ice Sheet releases large amounts of freshwater into the fjords around Greenland and many fjords are in direct contact with the ice sheet through tidewater outlet glaciers. Here we present the first seasonal hydrographic observations from the inner part of a sub-Arctic fjord, relatively close to and within 4–50 km of a fast-flowing tidewater outlet glacier. This region is characterized by a dense glacial and sea ice cover. Freshwater from runoff, subglacial freshwater (SgFW) discharge, glacial, and sea ice melt are observed above 50–90 m depth. During summer, SgFW and subsurface glacial melt mixed with ambient water are observed as a layered structure in the temperature profiles below the low-saline summer surface layer (<7 m). During winter, the upper water column is characterized by stepwise halo- and thermoclines formed by mixing between deeper layers and the surface layer influenced by ice melt. The warm (T > 1°C) intermediate water mass is a significant subsurface heat source for ice melt. We analyze the temperature and salinity profiles observed in late summer with a thermodynamic mixing model and determine the total freshwater content in the layer below the summer surface layer to be between 5% and 11%. The total freshwater contribution in this layer from melted glacial ice was estimated to be 1–2%, while the corresponding SgFW was estimated to be 3–10%. The winter measurements in the subsurface halocline layer showed a total freshwater content of about 1% and no significant contribution from SgFW. VL - 118 UR - http://dx.doi.org/10.1002/jgrc.20134 ER - TY - JOUR T1 - Outlet glacier response to forcing over hourly to interannual timescales, Jakobshavn Isbræ, Greenland JF - Journal of Glaciology Y1 - 2012 A1 - Podrasky, David A1 - Martin Truffer A1 - Mark Fahnestock A1 - Jason M Amundson A1 - Cassotto, Ryan A1 - Ian Joughin VL - 58 ER - TY - JOUR T1 - Submarine melting of the 1985 Jakobshavn Isbræ floating tongue and the triggering of the current retreat JF - Journal of Geophysical Research Y1 - 2011 A1 - Roman J. Motyka A1 - Martin Truffer A1 - Mark Fahnestock A1 - Mortensen, J. A1 - Rysgaard, S. A1 - I M Howat VL - 116 ER - TY - JOUR T1 - Ice mélange dynamics and implications for terminus stability, Jakobshavn Isbræ, Greenland JF - Journal of Geophysical Research Y1 - 2010 A1 - Jason M Amundson A1 - Mark Fahnestock A1 - Martin Truffer A1 - Brown, J. A1 - M P Lüthi A1 - Roman J. Motyka VL - 115 ER - TY - JOUR T1 - Volume change of Jakobshavn Isbrae, West Greenland:: 198519972007 JF - Journal of Glaciology Y1 - 2010 A1 - Roman J. Motyka A1 - Mark Fahnestock A1 - Martin Truffer VL - 56 UR - http://openurl.ingenta.com/content/xref?genre=article&issn=0022-1430&volume=56&issue=198&spage=635 ER - TY - JOUR T1 - Calving icebergs indicate a thick layer of temperate ice at the base of Jakobshavn Isbræ, Greenland JF - Journal of Glaciology Y1 - 2009 A1 - M P Lüthi A1 - Mark Fahnestock A1 - Martin Truffer VL - 55 UR - http://openurl.ingenta.com/content/xref?genre=article&issn=0022-1430&volume=55&issue=191&spage=563 ER - TY - JOUR T1 - Continued evolution of Jakobshavn Isbrae following its rapid speedup JF - J. geophys. Res Y1 - 2008 A1 - Ian Joughin A1 - I M Howat A1 - Mark Fahnestock A1 - B  E Smith A1 - Krabill, W. A1 - Alley, R.B. A1 - Stern, H. A1 - Martin Truffer VL - 113 UR - http://www.agu.org/pubs/crossref/2008/2008JF001023.shtml ER - TY - JOUR T1 - Glacier, fjord, and seismic response to recent large calving events, Jakobshavn Isbræ, Greenland JF - Geophysical Research Letters Y1 - 2008 A1 - Jason M Amundson A1 - Martin Truffer A1 - M P Lüthi A1 - Mark Fahnestock A1 - West, M. A1 - Roman J. Motyka VL - 35 UR - http://www.agu.org/pubs/crossref/2008/2008GL035281.shtml ER - TY - JOUR T1 - Ice-front variation and tidewater behavior on Helheim and Kangerdlugssuaq Glaciers, Greenland JF - Journal of Geophysical Research Y1 - 2008 A1 - Ian Joughin A1 - I M Howat A1 - Alley, R.B. A1 - Ekstrom, G. A1 - Mark Fahnestock A1 - Moon, T. A1 - Nettles, M. A1 - Martin Truffer A1 - Tsai, V.C. VL - 113 UR - http://www.agu.org/pubs/crossref/2008/2007JF000837.shtml ER - TY - JOUR T1 - Rethinking ice sheet time scales JF - Science Y1 - 2007 A1 - Martin Truffer A1 - Mark Fahnestock VL - 315 ER -