%0 Journal Article %J Geophysical Research Letters %D 2013 %T Rapid Submarine Melting Driven by Subglacial Discharge, LeConte Glacier, Alaska %A Roman J. Motyka %A Dryer, W. P. %A Jason M Amundson %A Martin Truffer %A Mark Fahnestock %K frontal ablation %K submarine melting %K tidewater glaciers %X 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. %B Geophysical Research Letters %V 40 %G eng %U http://dx.doi.org/10.1002/grl.51011 %R 10.1002/grl.51011 %0 Journal Article %J Journal of Geophysical Research: Oceans %D 2013 %T On the seasonal freshwater stratification in the proximity of fast-flowing tidewater outlet glaciers in a sub-Arctic sill fjord %A Mortensen, J. %A Bendtsen, J. %A Roman J. Motyka %A Lennert, K. %A Martin Truffer %A Mark Fahnestock %A Rysgaard, S. %K fjord %K freshwater sources and their distribution %K Greenland Ice Sheet %K subglacial freshwater fraction model %K subsurface heat sources for glacial ice melt %K tidewater outlet glaciers %X 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. %B Journal of Geophysical Research: Oceans %V 118 %P 1382–1395 %G eng %U http://dx.doi.org/10.1002/jgrc.20134 %R 10.1002/jgrc.20134 %0 Journal Article %J Journal of Glaciology %D 2012 %T Outlet glacier response to forcing over hourly to interannual timescales, Jakobshavn Isbræ, Greenland %A Podrasky, David %A Martin Truffer %A Mark Fahnestock %A Jason M Amundson %A Cassotto, Ryan %A Ian Joughin %B Journal of Glaciology %V 58 %P 1212 %G eng %R 10.3189/2012JoG12J065 %0 Journal Article %J Journal of Geophysical Research %D 2011 %T Submarine melting of the 1985 Jakobshavn Isbræ floating tongue and the triggering of the current retreat %A Roman J. Motyka %A Martin Truffer %A Mark Fahnestock %A Mortensen, J. %A Rysgaard, S. %A I M Howat %B Journal of Geophysical Research %V 116 %P F01007 %G eng %R 10.1029/2009JF001632 %0 Journal Article %J Journal of Geophysical Research %D 2010 %T Ice mélange dynamics and implications for terminus stability, Jakobshavn Isbræ, Greenland %A Jason M Amundson %A Mark Fahnestock %A Martin Truffer %A Brown, J. %A M P Lüthi %A Roman J. Motyka %B Journal of Geophysical Research %V 115 %P F01005 %G eng %R 10.1029/2009JF001405 %0 Journal Article %J Journal of Glaciology %D 2010 %T Volume change of Jakobshavn Isbrae, West Greenland:: 198519972007 %A Roman J. Motyka %A Mark Fahnestock %A Martin Truffer %B Journal of Glaciology %V 56 %P 635–646 %G eng %U http://openurl.ingenta.com/content/xref?genre=article&issn=0022-1430&volume=56&issue=198&spage=635 %0 Journal Article %J Journal of Glaciology %D 2009 %T Calving icebergs indicate a thick layer of temperate ice at the base of Jakobshavn Isbræ, Greenland %A M P Lüthi %A Mark Fahnestock %A Martin Truffer %B Journal of Glaciology %V 55 %P 563–566 %G eng %U http://openurl.ingenta.com/content/xref?genre=article&issn=0022-1430&volume=55&issue=191&spage=563 %0 Journal Article %J J. geophys. Res %D 2008 %T Continued evolution of Jakobshavn Isbrae following its rapid speedup %A Ian Joughin %A I M Howat %A Mark Fahnestock %A B  E Smith %A Krabill, W. %A Alley, R.B. %A Stern, H. %A Martin Truffer %B J. geophys. Res %V 113 %P F04006 %G eng %U http://www.agu.org/pubs/crossref/2008/2008JF001023.shtml %0 Journal Article %J Geophysical Research Letters %D 2008 %T Glacier, fjord, and seismic response to recent large calving events, Jakobshavn Isbræ, Greenland %A Jason M Amundson %A Martin Truffer %A M P Lüthi %A Mark Fahnestock %A West, M. %A Roman J. Motyka %B Geophysical Research Letters %V 35 %P L22501 %G eng %U http://www.agu.org/pubs/crossref/2008/2008GL035281.shtml %0 Journal Article %J Journal of Geophysical Research %D 2008 %T Ice-front variation and tidewater behavior on Helheim and Kangerdlugssuaq Glaciers, Greenland %A Ian Joughin %A I M Howat %A Alley, R.B. %A Ekstrom, G. %A Mark Fahnestock %A Moon, T. %A Nettles, M. %A Martin Truffer %A Tsai, V.C. %B Journal of Geophysical Research %V 113 %P F01004 %G eng %U http://www.agu.org/pubs/crossref/2008/2007JF000837.shtml %0 Journal Article %J Science %D 2007 %T Rethinking ice sheet time scales %A Martin Truffer %A Mark Fahnestock %B Science %V 315 %P 1508–1510 %G eng %R 10.1126/science.11404