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 - Seasonal to decadal scale variations in the surface velocity of Jakobshavn Isbrae, Greenland: Observation and model-based analysis JF - J. Geophys. Res. Y1 - 2012 A1 - Joughin, Ian A1 - Smith, B. E. A1 - Howat, I. M. A1 - Floricioiu, Dana A1 - Alley, Richard B. A1 - Truffer, M. A1 - Fahnestock, M.A. KW - glacier KW - glaciology KW - ice stream VL - 117 UR - http://www.agu.org/pubs/crossref/2012/2011JF002110.shtml 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 -