Asynchronous behavior of outlet glaciers feeding Godthåbsfjord (Nuup Kangerlua) and the triggering of Narsap Sermia's retreat in SW Greenland

We assess ice loss and velocity changes between 1985 and 2014 of three tidewater and fiveland terminating glaciers in Godthabsfjord (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 melange and conclude that the 2010-14 NS retreat was triggered by a combination of factors but primarily by an increase in submarine melting.We thank W. Dryer and D. Podrasky for assistance with fieldwork and L. Kenefic for assisting with digitizing glacier front positions. CH2 M HILL Polar Services and Air Greenland provided logistics support. The SPOT-5 images used for the 2008 DEM were provided by the SPIRIT program (Centre National d'Etudes Spatiales, France). The DigitalGlobe Worldview images used for the 2014 DEM were obtained from P. Morin. Terminus positions were derived from Landsat images courtesy of the U.S. Geological Survey. Funding was provided by the US National Science Foundation (NSF) Office of Polar Programs (OPP) grants NSF PLR-0909552 and NSF PLR-0909333. Cassotto is supported by NASA under the Earth and Space Science Fellowship Program (Grant NNX14AL29H). K. K. Kjeldsen acknowledges support from the Danish Council Research for Independent Research (grant no. DFF-409000151). K. Kjaer is thanked for his support during the earlier phases of this study. On-ice weather stations are operated by GEUS (Denmark) within the Programme for Monitoring of the Greenland Ice Sheet (PROMICE). J. Mortensen acknowledges support from IIKNN (Greenland), DEFROST project of the Nordic Centre of Excellence program "Interaction between Climate Change and the Cryosphere" and the Greenland Ecosystem Monitoring Programme (www. g-e-m. dk).S. Rysgaard was funded by the Canada Excellence Research Chair Programme. Additional funding was provided by the Geophysical Institute, University of Alaska Fairbanks, and Greenland Climate Research Centre. Scientific editor H. Fricker and reviewers H. Jiskoot and G. Cogley provided very constructive feedback that helped improve the paper.Peer ReviewedRitrýnt tímari