TY - JOUR T1 - Circumpolar Deep Water Impacts Glacial Meltwater Export and Coastal Biogeochemical Cycling Along the West Antarctic Peninsula JF - Frontiers in Marine Science Y1 - 2019 A1 - Cape, Mattias R. A1 - Vernet, Maria A1 - Pettit, Erin C. A1 - Wellner, Julia A1 - Truffer, Martin A1 - Akie, Garrett A1 - Domack, Eugene A1 - Leventer, Amy A1 - Smith, Craig R. A1 - Huber, Bruce A. KW - Antarctic Peninsula KW - ice KW - meltwater KW - phytoplankton VL - 6 UR - https://www.frontiersin.org/article/10.3389/fmars.2019.00144/full ER - TY - JOUR T1 - Contribution of the Greenland Ice Sheet to sea level over the next millennium JF - Science Advances Y1 - 2019 A1 - Aschwanden, Andy A1 - Fahnestock, Mark A. A1 - Truffer, Martin A1 - Brinkerhoff, Douglas J. A1 - Hock, Regine A1 - Khroulev, Constantine A1 - Mottram, Ruth A1 - Khan, S. Abbas AB - The Greenland Ice Sheet holds 7.2 m of sea level equivalent and in recent decades, rising temperatures have led to accelerated mass loss. Current ice margin recession is led by the retreat of outlet glaciers, large rivers of ice ending in narrow fjords that drain the interior. We pair an outlet glacier–resolving ice sheet model with a comprehensive uncertainty quantification to estimate Greenland's contribution to sea level over the next millennium. We find that Greenland could contribute 5 to 33 cm to sea level by 2100, with discharge from outlet glaciers contributing 8 to 45% of total mass loss. Our analysis shows that uncertainties in projecting mass loss are dominated by uncertainties in climate scenarios and surface processes, whereas uncertainties in calving and frontal melt play a minor role. We project that Greenland will very likely become ice free within a millennium without substantial reductions in greenhouse gas emissions. VL - 5 UR - http://advances.sciencemag.org/lookup/doi/10.1126/sciadv.aav9396 ER - TY - JOUR T1 - The Larsen Ice Shelf System, Antarctica (LARISSA): Polar Systems Bound Together, Changing Fast JF - GSA Today Y1 - 2019 A1 - Wellner, Julia A1 - Scambos, Ted A1 - Domack, Eugene A1 - Vernet, Maria A1 - Leventer, Amy A1 - Balco, Greg A1 - Brachfeld, Stefanie A1 - Cape, Mattias A1 - Huber, Bruce A1 - Ishman, Scott A1 - McCormick, Michael A1 - Mosley-Thompson, Ellen A1 - Pettit, Erin A1 - Smith, Craig A1 - Truffer, Martin A1 - Van Dover, Cindy A1 - Yoo, Kyu-Cheul AB - Climatic, cryospheric, and biologic changes taking place in the northern Antarctic Peninsula provide examples for how ongoing systemic change may pro‐ gress through the entire Antarctic system. A large, interdisciplinary research project focused on the Larsen Ice Shelf system, synthesized here, has documented dramatic ice cover, oceanographic, and ecosystem changes in the Antarctic Peninsula during the Holocene and the present period of rapid regional warming. The responsive- ness of the region results from its position in the climate and ocean system, in which a narrow continental block extends across zonal atmospheric and ocean flow, creating high snow accumulation, strong gradients and gyres, dynamic oceanography, outlet glaciers feeding into many fjords and bays having steep topography, and a continental shelf that contains many glacially carved troughs separated by areas of glacial sedi- ment accumulation. The microcosm of the northern Antarctic Peninsula has a ten- dency to change rapidly—rapid relative not just to Antarctica's mainland but compared to the rest of the planet as well—and it is generally warmer than the rest of Antarctica. Both its Holocene and modern glaciological retreats offer a picture of how larger areas of Antarctica farther south might change under future warming. VL - 29 ER - TY - JOUR T1 - Non-linear glacier response to calving events, Jakobshavn Isbræ, Greenland JF - Journal of Glaciology Y1 - 2019 A1 - Cassotto, Ryan A1 - Fahnestock, Mark A1 - Amundson, Jason M. A1 - Truffer, Martin A1 - Boettcher, Margaret S. A1 - De La Peña, Santiago A1 - Howat, Ian KW - calving KW - dynamic thinning KW - Jakobshavn Isbræ KW - terrestrial radar interferometry KW - tidewater glaciers AB - Jakobshavn Isbræ, a tidewater glacier that produces some of Greenland's largest icebergs and highest speeds, reached record-high flow rates in 2012 (Joughin and others, 2014). We use terrestrial radar interferometric observations from August 2012 to characterize the events that led to record-high flow. We find that the highest speeds occurred in response to a small calving retreat, while several larger calving events produced negligible changes in glacier speed. This non-linear response to calving events suggests the terminus was close to flotation and therefore highly sensitive to terminus position. Our observations indicate that a glacier's response to calving is a consequence of two competing feedbacks: (1) an increase in strain rates that leads to dynamic thinning and faster flow, thereby promoting destabilization, and (2) an increase in flow rates that advects thick ice toward the terminus and promotes restabilization. The competition between these feedbacks depends on temporal and spatial variations in the glacier's proximity to flotation. This study highlights the importance of dynamic thinning and advective processes on tidewater glacier stability, and further suggests the latter may be limiting the current retreat due to the thick ice that occupies Jakobshavn Isbræ's retrograde bed. VL - 65 ER - TY - JOUR T1 - Tracking icebergs with time-lapse photography and sparse optical flow , LeConte Bay , Alaska , 2016 – 2017 JF - J. Glaciol. Y1 - 2019 A1 - Kienholz, Christian A1 - Amundson, Jason M A1 - Motyka, Roman J A1 - Jackson, Rebecca H A1 - Mickett, John B A1 - Sutherland, David A A1 - Nash, Jonathan D A1 - Winters, Dylan S A1 - Dryer, William P A1 - Truffer, Martin KW - glaciological instruments and methods KW - ice KW - icebergs KW - ocean interactions KW - Remote sensing VL - 65 ER - TY - JOUR T1 - Active seismic studies in valley glacier settings: strategies and limitations JF - Journal of Glaciology Y1 - 2018 A1 - ZECHMANN, JENNA M. A1 - BOOTH, ADAM D. A1 - Truffer, Martin A1 - Gusmeroli, Alessio A1 - Amundson, Jason M. A1 - Larsen, Christopher F. KW - glacial tills KW - glacier geophysics KW - glaciological instruments and methods KW - seismics KW - subglacial AB - Subglacial tills play an important role in glacier dynamics but are difficult to characterize in situ. Amplitude Variation with Angle (AVA) analysis of seismic reflection data can distinguish between stiff tills and deformable tills. However, AVA analysis in mountain glacier environments can be problematic: reflections can be obscured by Rayleigh wave energy scattered from crevasses, and complex basal topography can impede the location of reflection points in 2-D acquisitions. We use a forward model to produce challenging synthetic seismic records in order to test the efficacy of AVA in crevassed and geometrically complex environments. We find that we can distinguish subglacial till types in moderately crevassed environments, where ‘moderate' depends on crevasse spacing and orientation. The forward model serves as a planning tool, as it can predict AVA success or failure based on characteristics of the study glacier. Applying lessons from the forward model, we perform AVA on a seismic dataset collected from Taku Glacier in Southeast Alaska in March 2016. Taku Glacier is a valley glacier thought to overlay thick sediment deposits. A near-offset polarity reversal confirms that the tills are deformable. VL - 64 UR - https://www.cambridge.org/core/product/identifier/S0022143018000692/type/journal{\_}article ER - TY - JOUR T1 - Acquisition of a 3 min, two-dimensional glacier velocity field with terrestrial radar interferometry JF - Journal of Glaciology Y1 - 2017 A1 - Voytenko, Denis A1 - Dixon, Timothy H. A1 - Holland, David M. A1 - Cassotto, Ryan A1 - Howat, Ian M. A1 - Fahnestock, Mark A. A1 - Truffer, Martin A1 - De La Peña, Santiago KW - glacier flow KW - glacier geophysics KW - glaciological instruments and methods AB - {\textless}p{\textgreater}Outlet glaciers undergo rapid spatial and temporal changes in flow velocity during calving events. Observing such changes requires both high temporal and high spatial resolution methods, something now possible with terrestrial radar interferometry. While a single such radar provides line-of-sight velocity, two radars define both components of the horizontal flow field. To assess the feasibility of obtaining the two-dimensional (2-D) flow field, we deployed two terrestrial radar interferometers at Jakobshavn Isbrae, a major outlet glacier on Greenland's west coast, in the summer of 2012. Here, we develop and demonstrate a method to combine the line-of-sight velocity data from two synchronized radars to produce a 2-D velocity field from a single (3 min) interferogram. Results are compared with the more traditional feature-tracking data obtained from the same radar, averaged over a longer period. We demonstrate the potential and limitations of this new dual-radar approach for obtaining high spatial and temporal resolution 2-D velocity fields at outlet glaciers.{\textless}/p{\textgreater} UR - https://www.cambridge.org/core/product/identifier/S0022143017000284/type/journal{\_}article ER - TY - JOUR T1 - Asynchronous behavior of outlet glaciers feeding Godth\aabsfjord (Nuup Kangerlua) and the triggering of Narsap Sermia's retreat in SW Greenland JF - J. Glaciol. Y1 - 2017 A1 - Motyka, Roman J. A1 - Cassotto, Ryan A1 - Truffer, Martin A1 - Kjeldsen, Kristian K. A1 - Van As, Dirk A1 - Korsgaard, Niels J. A1 - Fahnestock, Mark A1 - Howat, Ian A1 - Langen, Peter L. A1 - Mortensen, John A1 - Lennert, Kunuk A1 - Rysgaard, Søren KW - glacier calving KW - glacier discharge KW - glacier mass balance KW - ice/atmosphere interactions KW - ice/ocean interactions KW - tidewater glaciers AB - We assess ice loss and velocity changes between 1985 and 2014 of three tidewater and five-land terminating glaciers in Godth{\aa}bsfjord (Nuup Kangerlua), Greenland. Glacier thinning accounted for 43.8 ± 0.2 km 3 of ice loss, equivalent to 0.10 mm eustatic sea-level rise. An additional 3.5 ± 0.3 km 3 was lost to the calving retreats of Kangiata Nunaata Sermia (KNS) and Narsap Sermia (NS), two tidewater glaciers that exhibited asynchronous behavior over the study period. KNS has retreated 22 km from its Little Ice Age (LIA) maximum (1761 AD), of which 0.8 km since 1985. KNS has stabilized in shallow water, but seasonally advects a 2 km long floating tongue. In contrast, NS began retreating from its LIA moraine in 2004–06 (0.6 km), re-stabilized, then retreated 3.3 km during 2010–14 into an over-deepened basin. Velocities at KNS ranged 5–6 km a −1 , while at NS they increased from 1.5 to 5.5 km a −1 between 2004 and 2014. We present comprehensive analyses of glacier thinning, runoff, surface mass balance, ocean conditions, submarine melting, bed topography, ice mélange and conclude that the 2010–14 NS retreat was triggered by a combination of factors but primarily by an increase in submarine melting. VL - 63 ER - TY - JOUR T1 - Error sources in basal yield stress inversions for Jakobshavn Isbræ, Greenland, derived from residual patterns of misfit to observations JF - Journal of Glaciology Y1 - 2017 A1 - Habermann, Marijke A1 - Truffer, Martin A1 - Maxwell, David KW - glacier modeling KW - ice-sheet modeling KW - subglacial processes AB - The basal interface of glaciers is generally not directly observable. Geophysical inverse methods are therefore used to infer basal parameters from surface observations. Such methods can also provide information about potential inadequacies of the forward model. Ideally an inverse problem can be regularized so that the differences between modeled and observed surface velocities reflect observational errors. However, deficiencies in the forward model usually result in additional errors. Here we use the spatial pattern of velocity residuals to discuss the main error sources for basal stress inversions for Jakobshavn Isbræ, Greenland. Synthetic tests with prescribed patterns of basal yield stress with varying length scales are then used to investigate different weighting functions for the data-model misfit and for the ability of the inversion to resolve details in basal yield stress. We also test real-data inversions for their sensitivities to prior estimate, forward model parameters, data gaps, and temperature fields. We find that velocity errors are not sufficient to explain the residual patterns of real-data inversions. Conversely, ice-geometry errors and especially simulated errors in model simplifications are capable of reproducing similar error patterns and magnitudes. We suggest that residual patterns can provide useful guidance for forward model improvements. VL - 63 UR - https://www.cambridge.org/core/product/identifier/S0022143017000612/type/journal{\_}article ER - TY - JOUR T1 - Mass Balance Evolution of Black Rapids Glacier, Alaska, 1980–2100, and Its Implications for Surge Recurrence JF - Frontiers in Earth Science Y1 - 2017 A1 - Kienholz, Christian A1 - Hock, Regine A1 - Truffer, Martin A1 - Bieniek, Peter A1 - Lader, Richard AB - Surge-type Black Rapids Glacier, Alaska, has undergone strong retreat since it last surged in 1936-37. To assess its evolution during the late 20th and 21st centuries and determine potential implications for surge likelihood, we run a simplified glacier model over the periods 1980-2015 (hindcasting) and 2015-2100 (forecasting). The model is forced by daily temperature and precipitation fields, with downscaled reanalysis data used for the hindcasting. A constant climate scenario and an RCP 8.5 scenario based on the GFDL-CM3 climate model are employed for the forecasting. Debris evolution is accounted for by a debris layer time series derived from satellite imagery (hindcasting) and a parametrized debris evolution model (forecasting). A retreat model accounts for the evolution of the glacier geometry. Model calibration, validation and parametrization rely on an extensive set of in situ and remotely sensed observations. To explore uncertainties in our projections, we run the glacier model in a Monte Carlo fashion, varying key model parameters and input data within plausible ranges. Our results for the hindcasting period indicate a negative mass balance trend, caused by atmospheric warming in the summer, precipitation decrease in the winter and surface elevation lowering (climate-elevation feedback), which exceed the moderating effects from increasing debris cover and glacier retreat. Without the 2002 rockslide deposits on Black Rapids' lower reaches, the mass balances would be more negative, by  20% between the 2003 and 2015 mass-balance years. Despite its retreat, Black Rapids Glacier is substantially out of balance with the current climate. By 2100,  8% of Black Rapids' 1980 area are projected to vanish under the constant climate scenario and  73% under the RCP 8.5 scenario. For both scenarios, the remaining glacier portions are out of balance, suggesting continued retreat after 2100. Due to mass starvation, a surge in the 21st century is unlikely. The projected retreat will affect the glacier's runoff and change the landscape in the Black Rapids area markedly. VL - 5 UR - http://journal.frontiersin.org/article/10.3389/feart.2017.00056 ER - TY - JOUR T1 - Sediment transport drives tidewater glacier periodicity Y1 - 2017 A1 - Brinkerhoff, Douglas A1 - Truffer, Martin A1 - Aschwanden, Andy AB - Most of Earth’s glaciers are retreating, but some tidewater glaciers are advancing despite increasing temperatures and contrary to their neighbors. This can be explained by the coupling of ice and sediment dynamics: a shoal forms at the glacier terminus, reducing ice discharge and causing advance towards an unstable configuration followed by abrupt retreat, in a process known as the tidewater glacier cycle. Here we use a numerical model calibrated with observations to show that interactions between ice flow, glacial erosion, and sediment transport drive these cycles, which occur independent of climate variations. Water availability controls cycle period and amplitude, and enhanced melt from future warming could trigger advance even in glaciers that are steady or retreating, complicating interpretations of glacier response to climate change. The resulting shifts in sediment and meltwater delivery from changes in glacier configuration may impact interpretations of marine sediments, fjord geochemistry, and marine ecosystems. VL - 8 SN - 2041-1723 UR - https://doi.org/10.1038/s41467-017-00095-5 IS - 1 JO - Nature Communications ER - TY - JOUR T1 - Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier JF - Nature Y1 - 2017 A1 - Smith, J. A. A1 - Andersen, T. J. A1 - Shortt, M. A1 - Gaffney, A. M. A1 - Truffer, Martin A1 - Stanton, T P A1 - Bindschadler, Robert A1 - Dutrieux, Pierre A1 - Jenkins, Adrian A1 - Hillenbrand, C.-D. A1 - Ehrmann, Werner A1 - Corr, H. F. J. A1 - Farley, N. A1 - Crowhurst, S. A1 - Vaughan, David G. KW - Antarctica KW - Pine Island glacier AB - The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line—which marks the boundary between grounded ice and floating ice shelf—is underway. Understanding this recent retreat requires a detailed knowledge of grounding-line history, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreat is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Thus our results suggest that, even when climate forcing weakened, ice-sheet retreat continued. VL - 541 UR - http://dx.doi.org/10.1038/nature20136{%}5Cnhttp://www.nature.com/doifinder/10.1038/nature20136 http://www.nature.com/articles/nature20136 ER - TY - JOUR T1 - Automated detection of unstable glacier flow and a spectrum of speedup behavior in the Alaska Range JF - Journal of Geophysical Research F: Earth Surface Y1 - 2016 A1 - Herreid, Sam A1 - Truffer, Martin KW - automated detection KW - debris cover KW - pulse-type glaciers KW - spectrum of glacier flow instabilities KW - surge-type glaciers VL - 121 ER - TY - JOUR T1 - Bayesian Inference of Subglacial Topography Using Mass Conservation JF - Frontiers in Earth Science Y1 - 2016 A1 - Brinkerhoff, Douglas J A1 - Aschwanden, Andy A1 - Truffer, Martin AB - We develop a Bayesian model for estimating ice thickness given sparse observations coupled with estimates of surface mass balance, surface elevation change, and surface velocity. These fields are related through mass conservation. We use the Metropolis-Hastings algorithm to sample from the posterior probability distribution of ice thickness for three cases: a synthetic mountain glacier, ̈ Storglaci aren, and Jakobshavn Isbræ. Use of continuity in interpolation improves thickness estimates where relative velocity and surface mass balance errors are small, a condition difficult to maintain in regions of slow flow and surface mass balance near zero. Estimates of thickness uncertainty depend sensitively on spatial correlation. When this structure is known, we suggest a thickness measurement spacing of one to two times the correlation length to take best advantage of continuity based interpolation techniques. To determine ideal measurement spacing, the structure of spatial correlation must be better quantified. VL - 4 UR - http://journal.frontiersin.org/article/10.3389/feart.2016.00008 ER - TY - JOUR T1 - Complex Greenland outlet glacier flow captured JF - Nature Communications Y1 - 2016 A1 - Aschwanden, Andy A1 - Fahnestock, Mark A A1 - Truffer, Martin VL - 7 UR - http://www.nature.com/doifinder/10.1038/ncomms10524 ER - TY - JOUR T1 - Sensitivity of Pine Island Glacier to observed ocean forcing JF - Geophysical Research Letters Y1 - 2016 A1 - Christianson, Knut A1 - Bushuk, Mitchell A1 - Dutrieux, Pierre A1 - Parizek, Byron R. A1 - Joughin, Ian R. A1 - Alley, Richard B. A1 - Shean, David E. A1 - Abrahamsen, E. Povl A1 - Anandakrishnan, Sridhar A1 - Heywood, Karen J. A1 - Kim, Tae-Wan A1 - Lee, Sang Hoon A1 - Nicholls, Keith A1 - Stanton, Tim A1 - Truffer, Martin A1 - Webber, Benjamin G. M. A1 - Jenkins, Adrian A1 - Jacobs, Stan A1 - Bindschadler, Robert A1 - Holland, David M. KW - glacier-ocean interactions KW - Ice Dynamics KW - ice shelves KW - ice streams KW - marine ice sheet instability AB - ©2016. American Geophysical Union. All Rights Reserved.We present subannual observations (2009–2014) of a major West Antarctic glacier (Pine Island Glacier) and the neighboring ocean. Ongoing glacier retreat and accelerated ice flow were likely triggered a few decades ago by increased ocean-induced thinning, which may have initiated marine ice sheet instability. Following a subsequent 60{%} drop in ocean heat content from early 2012 to late 2013, ice flow slowed, but by {\textless} 4{%}, with flow recovering as the ocean warmed to prior temperatures. During this cold-ocean period, the evolving glacier-bed/ice shelf system was also in a geometry favorable to stabilization. However, despite a minor, temporary decrease in ice discharge, the basin-wide thinning signal did not change. Thus, as predicted by theory, once marine ice sheet instability is underway, a single transient high-amplitude ocean cooling has only a relatively minor effect on ice flow. The long-term effects of ocean temperature variability on ice flow, however, are not yet known. VL - 43 UR - http://doi.wiley.com/10.1002/2016GL070500 ER - TY - JOUR T1 - The taphonomy of human remains in a glacial environment JF - Forensic Science International Y1 - 2016 A1 - Pilloud, Marin A. A1 - Megyesi, Mary S. A1 - Truffer, Martin A1 - Congram, Derek KW - Forensic anthropology KW - Glacial dynamics KW - Glacial movement KW - Glacial taphonomy AB - A glacial environment is a unique setting that can alter human remains in characteristic ways. This study describes glacial dynamics and how glaciers can be understood as taphonomic agents. Using a case study of human remains recovered from Colony Glacier, Alaska, a glacial taphonomic signature is outlined that includes: (1) movement of remains, (2) dispersal of remains, (3) altered bone margins, (4) splitting of skeletal elements, and (5) extensive soft tissue preservation and adipocere formation. As global glacier area is declining in the current climate, there is the potential for more materials of archaeological and medicolegal significance to be exposed. It is therefore important for the forensic anthropologist to have an idea of the taphonomy in this setting and to be able to differentiate glacial effects from other taphonomic agents. VL - 261 UR - http://dx.doi.org/10.1016/j.forsciint.2016.01.027 ER - TY - JOUR T1 - Seasonal and interannual variations in ice melange and its impact on terminus stability, Jakobshavn Isbræ, Greenland JF - Journal of Glaciology Y1 - 2015 A1 - Cassotto, Ryan A1 - Fahnestock, Mark A1 - Amundson, Jason M. A1 - Truffer, Martin A1 - Joughin, Ian KW - arctic glaciology KW - calving KW - ice KW - ocean interactions KW - Remote sensing KW - sea-ice dynamics VL - 61 ER - TY - JOUR T1 - Tidal and seasonal variations in calving flux observed with passive seismology JF - Journal of Geophysical Research: Earth Surface Y1 - 2015 A1 - Bartholomaus, Timothy C A1 - Larsen, Christopher F A1 - West, Michael E A1 - O'Neel, Shad A1 - Pettit, Erin C A1 - Truffer, Martin ER - TY - RPRT T1 - Ice Thickness Measurements on the Harding Icefield , Kenai Peninsula , Alaska Y1 - 2014 A1 - Truffer, Martin ER - TY - JOUR T1 - Quantifying velocity response to ocean tides and calving near the terminus of Jakobshavn Isbræ, Greenland JF - Journal of Glaciology Y1 - 2014 A1 - Podrasky, David A1 - Truffer, Martin A1 - Lüthi, Martin A1 - Fahnestock, Mark KW - calving KW - glacier fluctuations KW - ice KW - ocean interactions VL - 60 UR - http://www.igsoc.org/journal/60/222/t13J130.html ER - TY - JOUR T1 - Outlet glacier response to forcing over hourly to interannual timescales, Jakobshavn Isbræ, Greenland JF - J. Glaciol. Y1 - 2012 A1 - Podrasky, David A1 - Truffer, Martin A1 - Fahnestock, Mark A1 - Amundson, Jason M. A1 - Cassotto, Ryan A1 - Joughin, Ian VL - 58 UR - http://openurl.ingenta.com/content/xref?genre=article{&}issn=0022-1430{&}volume=58{&}issue=212{&}spage=1212 ER - TY - JOUR T1 - Ice-front variation and tidewater behavior on Helheim and Kangerdlugssuaq Glaciers, Greenland JF - Journal of Geophysical Research: Earth Surface Y1 - 2008 A1 - Joughin, Ian A1 - Howat, Ian A1 - Alley, Richard B. A1 - Ekstrom, Goran A1 - Fahnestock, Mark A1 - Moon, Twila A1 - Nettles, Meredith A1 - Truffer, Martin A1 - Tsai, Victor C. AB - We used satellite images to examine the calving behavior ofHelheim and Kangerdlugssuaq Glaciers, Greenland, from 2001 to 2006, a period in which they retreated and speed up. These data show that many large iceberge-calving episodes coincided with teleseismically detected glacial erthquakes, suggesting that calving-related processes are the source of seismicity. For each of several events for which we hace observations, the ice front calved back to a large, pre-existing rift. These refits form where the ice has thinned to near flotation as the ice front retreats down back side of a bathymetric high, which agrees well with earlier theoretical predictions. In adition to recent retreat in a period of high temperature, analysis of several images shows that Helhaim retreated in the 20th Century during a warmer period and then re-adcanced during a subsequent cooler period. This apparent sensitivity to waming suggests that higher temperatures may promote an initial retread off a bathymetric high that is then sustained by tidewater dynamics as the ice front retreats into depper water. The cycle of frontal advance and retreat in less than a century indicates that tidewater glaciers in Greenland can advance rapidly. Greenland's larger resorvoir of inland ice and conditions that favor the formation of ice shelves likely contribute to the rapid rates of advance. VL - 113 SN - 0148-0227 UR - http://www.agu.org/pubs/crossref/2008/2007JF000837.shtml ER - TY - JOUR T1 - Record negative glacier balances and low velocities during the 2004 heatwave in Alaska, USA: implications for the interpretation of observations by Zwally and others in Greenland JF - Journal of Glaciology Y1 - 2005 A1 - Truffer, Martin A1 - Harrison, W.D. A1 - March, R.S. VL - 51 UR - http://openurl.ingenta.com/content/xref?genre=article{&}issn=0022-1430{&}volume=51{&}issue=175{&}spage=663 https://www.cambridge.org/core/product/identifier/S002214300021085X/type/journal{\_}article ER - TY - JOUR T1 - The sliding velocity over a sinusoidal bed at high water pressure JF - Journal of Glaciology Y1 - 1998 A1 - Truffer, Martin A1 - Iken, Almut VL - 44 ER -