 has been split into three geographical regions which are Northwest Greenland (3.1), North Greenland (3.2), and Northeast Greenland (3.3). Within North Greenland there are a further three sub-geographical regions, North NW (3.2.1), North Central (3.2.2), and North NE (3.2.3). Colored circles show a first order classification of potential surge-type glaciers across northern Greenland. Red circles show glaciers which are likely to be surge type based on clear surge-cycles having been recorded within the literature. Yellow circles show glaciers at which surging is possible based on glaciers which may have shown surge-characteristics, but either have not been referred to as surge-type or have not undergone a large surge event. Green circles show glaciers at which no evidence of surging has been recorded in the literature. Background image derived from NASA EOSDIS Worldview (16.07.15 and 21.07.15).
Figure 2. (A) Location of large floating ice tongues around the northern Greenland study region based on a review of the literature. Glacier abbreviations relate to Table 1. (B) Bed topography data across Greenland displayed as areas below sea level (<0 m), deep areas in red, shallower bed topography in blue. Both bed topography and floating ice tongue data were derived from the IceBridge BedMachine Greenland, Version 2 dataset in 2015 (Morlighem et al., 2015). (C) Glacier velocities (m a−1) during 2009/10 acquired from the MEaSUREs v2 Greenland velocity dataset (Joughin et al., 2010b) and catchment areas of northern Greenland outlet glaciers derived from hydrological analysis using the Morlighem et al. (2015) bed elevation and ice thickness datasets.
Regional Changes in Glacier Dynamics
Early scientific explorations of northern Greenland by Peary (1892) and the First (1912) and Second (1916–1918) Thule expeditions led by Rasmussen (1912, 1919) sought to improve understanding of the northern margin of the ice sheet. Subsequent studies identified large floating ice tongues, up to 50 km long, on many northern Greenland glaciers (Koch, 1928; Higgins, 1991). In this respect, they are unique in comparison to other regions of the ice sheet, where floating ice tongues are generally much shorter or absent. Historically, a significant proportion of northern Greenland glaciers are documented to have retreated, particularly between 1894 and 1962 (Davies and Krinsley, 1962). More recently, estimates of ice discharge in the late 1990s indicated widespread thinning (Rignot et al., 1997). Studies by Higgins (1991), Rignot et al. (1997), and Rignot et al. (2001) provided more comprehensive observations of glacier width, length, the presence of floating tongues, as well as initial velocity measurements and grounding line positions. Since then, a comprehensive analysis of northern Greenland glacier retreat and velocity fluctuations has not been conducted, although outlet glaciers from this region are often incorporated into GrIS wide studies (Moon and Joughin, 2008; Joughin et al., 2010a; Box and Decker, 2011; Murray et al., 2015). These syntheses reported significant increases in outlet glacier retreat rates across Greenland (for 1992–2006; Moon and Joughin, 2008) and that the largest cumulative area changes (during 2000–2010) occurred in northern Greenland, particularly at glaciers with the largest floating portions (e.g., Petermann, Humboldt, and Zachariae Isstrøm; Box and Decker, 2011).
An outline of the characteristics of each of the outlet glaciers in our study region is provided in Table 1, which also includes glacier catchment sizes delineated using bedrock topography and ice thickness data (Morlighem et al., 2014) input into the Shreve hydropotential formula (Shreve, 1972) to determine subglacial water routing and thus glacier drainage catchments. The following sections are a synthesis of previous work on each of the glaciers by region (Figure 1), with a focus on describing the key characteristics of each glacier and setting recent observations in a broader historical context. For comparison between sub-sections, we focus on terminus length