 changes, but in some cases where length is not reported in the literature, we refer to terminus change as it is reported in area.
Northwest Greenland (Figure 1), has recently undergone glacier retreat, particularly between 2000 and 2010 (Murray et al., 2015). Most outlets in this region have undergone long-term thinning (1994–2014; Csatho et al., 2014) and have accelerated by 28% between 2000 and 2010 (Moon et al., 2012). Three of the largest outlet glaciers in the far northwestern region are Harald Moltke Bræ, which drains into Wolstenholme Fjord, and Heilprin and Tracy Glaciers, which terminate in the neighboring Inglefield Bay (Figure 3).
Figure 3. (A) Location of studied glaciers in Northwest Greenland, including Harald Moltke Bræ, Heilprin, and Tracy Glaciers (green circles) and grounded ice (black line). Velocity data were acquired from the 2005/2006 MEaSUREs v2 Greenland velocity (Joughin et al., 2010b). Background imagery is from Landsat 8 (late summer 2015). (B) Estimated terminus positions from Wright (1939), showing changes between 1916 and 1932, and its position in 2015 (green). (C) Previous terminus positions for Tracy and Heilprin Glaciers (Dawes and van As, 2010) and the 2015 position (light blue).
Harald Moltke Bræ
Harald Moltke Bræ is an outlet glacier in northwest Greenland that is 6.3 km wide at its grounded terminus (Koch, 1928; Wright, 1939; Davies and Krinsley, 1962; Rignot et al., 2001; Figure 2). Early observations suggested that the terminus had two calving lobes (Wright, 1939) shown in Figure 3B. However, recent imagery shows this is no longer the case (Figure 3B). The catchment area of Harald Moltke Bræ is smaller than most other glaciers in the study area, draining only 1400 km2 (Table 1).
Early studies provided a detailed historical account of terminus change for the period 1916–1965 (Wright, 1939; Davies and Krinsley, 1962; Mock, 1966; Figure 3B). Between 1916 and 1926 the glacier retreated, which was followed by advance until 1932 when it reached a similar position as in 1916 (Wright, 1939; Davies and Krinsley, 1962; Mock, 1966). Between 1932 and 1937, the calving of large tabular icebergs was observed (Wright, 1939) and, by 1959, the terminus had retreated 5.5 km from its 1932 position (Davies and Krinsley, 1962). It is also known that the glacier underwent net retreat of 2.9 km between 2000 and 2010 (Murray et al., 2015).
From 1916 to 1965 the velocity of Harald Moltke Bræ fluctuated greatly between 30 and 1000 m a−1 (Mock, 1966). More recently, in 2000/01, the glacier was flowing at 30–100 m a−1 at the terminus, reaching up to a maximum of 300 m a−1 further up glacier (Joughin et al., 2010a). By 2005, the velocity at the terminus increased to 2000 m a−1 (Joughin et al., 2010a). Several authors have suggested these recent changes in velocity reflect surge behavior at Harald Moltke Bræ (Rignot and Kanagaratnam, 2006; Moon et al., 2012). In particular, velocity increase during 2005 coincided with terminus advance (1.2 km) in 2004/2005 (Murray et al., 2015).
Since the detailed work of Mock (1966), few studies have specifically focused on Harald Moltke Bræ. Its surge-like behavior is unusual in comparison to nearby outlet glaciers. Despite showing marked increases in velocity and advance during proposed surge events (Rignot and Kanagaratnam, 2006; Joughin et al., 2010a; Murray et al., 2015), the glacier has undergone large net retreat following surge events (Murray et al., 2015). This has led to a retreat of ~12 km compared to its position in 1916 (Figure 3B) and hints that the glacier has been influenced by longer-term external environmental drivers.
Heilprin and Tracy Glaciers
Heilprin and Tracy Glaciers are two large outlet glaciers in northwest Greenland that are 6.7 and 5 km wide, respectively (Table 1), and collectively drain an area of ~12,000 km2 into Inglefield Bay (Figure 3A). Davies and Krinsley (1962) noted that both glaciers had floating ice tongues in 1892, although early observations with limited data make this difficult to verify. Rignot et al. (2001) later found floating sec