Spatial and temporal variability of water-filled crevasse hydrologic states along the shear margins of Jakobshavn Isbrae, Greenland

Abstract

The impact of melt water injection into ice streams over the Greenland Ice Sheet is not well understood. Water-filled crevasses along the shear margins of Jakobshavn Isbrae are known to fill and drain, resulting in weakening of the shear margins due to reduced basal friction. Seasonal variability in the hydrologic dynamics of these features has not been 10 quantified. In this work, we characterize the spatial and temporal variability in the hydrological state (filled or drained) of these water-filled crevasse systems. A fusion of multi-sensor optical satellite imagery was used to examine hydrologic states from 2000 to 2015. The monthly distribution of crevasse systems observed as water filled is unimodal with peak number of filled days during the month of July at 329 days, while May has the least at 15. Over the study period the occurrence of drainage within a given season increases. Inter-seasonal drain frequencies over these systems ranged from 0 to 5. The 15 frequency of multi-drainage events are correlated with warmer seasons and large strain rates. Over the study period, summer temperatures averaged from -1 and 2 ⁰C and tensile strain rates have increased to as high as ~ 1.2 s -1 . Intermittent melt water input during hydrofracture drainage responsible for transporting surface water to the bed is largely facilitated by high local tensile stresses. Drainage due to fracture propagation may be increasingly modulated by ocean-induced calving dynamics for the lower elevation ponds. Water-filled crevasses could expand in extent and volume as temperatures increase resulting in 20 regional amplification of ice mass flux into the ice stream system. Motivation and Prior WorkThe Greenland Ice Sheet (GrIS) has experienced considerable mass loss over the last few decades (Krabill et al., 2004;Joughin et al., 2004;Alley et al., 2005aAlley et al., , 2005bLuthcke et al., 2006;Hanna et al., 2008) resulting in negative mass balance and substantive contribution to sea level rise (Rignot et al., 2008;van den Broeke et al., 2009; Shepherd et al., 2012). 25Commensurate with these changes has been the documented impact of surface meltwater on ice sheet velocity during the summer within the ablation zone (Zwally et al., 2002;Joughin et al., 2008; van de Wal et al., 2008;Shepherd et al., 2009;Bartholomew et al., 2010;Sundal et al., 2011;Palmer et al., 2011;Hoffman et al., 2011), via supraglacial lakes, channels, The Cryosphere Discuss., doi:10.5194/tc-2017Discuss., doi:10.5194/tc- -86, 2017 Manuscript under review for journal The Cryosphere Discussion started: 24 May 2017 c Author(s) 2017. CC-BY 3.0 License. 2and moulins largely beyond regions of fast flow (Echelmeyer et. al., 1991;Box and Ski, 2007; McMillan et al., 2007;Sneed and Hamilton, 2007;Das et al., 2008, Sundal et al, 2009Lampkin, 2011;Selmes et al., 2011; Tedesco and Steiner, 2011;Howat et al., 2013; Koenig et al., 2015). The presence of ponded water within regions of fast flow has received little attention. Lampkin et al. (2013) evaluated the spatial and tempora...

Toward Improved Understanding of Changes in Greenland Outlet Glacier Shear Margin Dynamics in a Warming Climate

“…Observed drainage rates of water-filled crevasses range from 0.001 to 0.012 km 2 d −1 over approximately 2 weeks to a month (Lampkin et al, 2013). Some water-filled crevasse systems have been observed to drain over shorter time intervals (<day) (Lampkin et al, 2013;Cavanagh et al, 2017;Joseph and Lampkin, 2017). There is considerable inter-annual variability in drainage events over these water-filled crevasse systems.…”

“…There is considerable inter-annual variability in drainage events over these water-filled crevasse systems. Multiple drainages within a single melt season are correlated with increases in average summer temperatures (Joseph and Lampkin, 2017). During more intense melt seasons, the opportunity for meltwater production increases.…”

“…The Landsat archive has sufficient samples to determine the trend in extent over the study period. Joseph and Lampkin (2017) have evaluated the seasonal variability in hydrologic state (filled vs. drained) and additional work will be completed to expand this assessment to changes in inundation extent.…”

“…Furthermore, Cavanagh et al (2017) documented an increase in extra-marginal ice flow of ∼20% associated with observed drainage from water-filled crevasse ponds during the 2013-2015 melt seasons and consistent with numerical simulations that predict a potential increase in flow of ∼35%. Joseph and Lampkin (2017) examined the temporal variability of hydrologic state (drained or filled) for each crevasse system using a fusion of data from several optical sensors and found significant annual variability in duration and timing of drainage. They also observed that some systems demonstrated multiple drainage events within a single melt season.…”