5.1. Observation of EGC/EGCC in SST Data
 In accordance with Bacon et al.  we interpret the cold water band at the coast in Landsat data and the equivalent negative coastal SSTA in the AVHRR data as the expression of the EGC/EGCC (Figures 7 and 9). Using typical widths for the EGCC from the work of Sutherland and Pickart , the SST of the EGCC was ∼2°C lower than the EGC as measured from Landsat thermal data comparing average temperature between 3–33 km and 22–63 km from the coast [Sutherland and Pickart, 2008]. The Landsat data show the EGCC was narrowest and least well defined in 2003–2004; however, by late September 2005, a wide cold coastal surface water current was present (Figure 9). The SSTA in the AVHRR data concur with this interpretation.
 The Landsat images from the Kangerdlugssuaq catchment (Figure 9a) provide strong evidence for the EGCC starting at this location, in accordance with Sutherland and Pickart , with little cold water transported along the coast from further north during this time of year. The images from 2000, 2005, and 2007 are the most supportive. However, our Landsat images do not support the suggestion that the EGCC forms due to the diversion of cold EGC waters through the Kangerdlugssuaq glacial trough (Figure 1) to the coast [Sutherland and Pickart, 2008]. Indeed, at Kangerdlugssuaq, the glacial trough appears to be delineated by high SSTs. While we must recognize that the SST is representative only of the very surface of the ocean, it is hard to explain the consistent high SSTs over the trough without warm water occurring at depth as well.
5.2. What Was the Cause of the Glacier Dynamic Event?
 The synchronous nature of the previously reported speedup and subsequent prolonged slowdown over such a large region rules out any local control, such as retreat of each glacier front into an overdeepening (as was suggested by Howat et al. ). Thus, we examine two regional triggers for these responses. First, we consider air temperature and increased runoff, and second, the influence of ocean temperatures.
 Our mass balance modeling shows runoff in southeast Greenland was at a minimum in 2003 and low again in 2004, despite above average coastal air temperatures. The acceleration of these glaciers therefore occurs at a time of low runoff. Runoff was particularly high in 2006, which matches the period of maximum slowdown. On this basis, we reject increased surface runoff as the controlling factor for the increased speed of these SE Greenland tidewater glaciers, since their speedup is synchronous with reduced runoff, and their slowdown coincided with maximum runoff.
 Although the presence of a thick snowpack would limit catchment-wide runoff, higher coastal air temperatures would cause more melt close to the exposed glacier front. This increased melt would potentially increase water input and levels in crevasses and could drive increased circulation at the calving front, both of which can increase iceberg calving rates [Benn et al., 2007; Motyka et al., 2003]. Coastal air temperatures at Tasiilaq were higher than usual during 2003–2005 (Figure 4a), whereas on 2006 and 2007 they were lower (albeit higher than 2000–2002). The minor reactivation at Helheim in 2007 occurred when air temperatures were not significantly higher than the preceding year (Figure 4a). Thus, there is no strong correlation between air temperature and the glacier dynamic changes we report. However, it should be noted that Tasiilaq is located close only to Helheim and Ikertivaq glaciers, and so, without further evidence, this effect cannot be wholly ruled out as the driver for these dynamic changes. Furthermore, coastal air temperatures and SST are clearly interrelated.
 The other regional factor linking the outlet glaciers in SE Greenland is the ocean [cf. D. M. Holland et al., 2008; Straneo et al., 2010]. Although the mooring data show water conditions only at a single point, the warm saline water recorded at depth in 2003 was clearly part of a widespread anomaly on the SE Greenland coast that year as evident in the satellite data: (1) SSTA and SST data show warmer coastal waters than normal, with warm water at the coast by late summer 2003 (August and September; Figures 7 and 9); (2) there was a high-salinity cap on the shelf waters at Kap Farvel (location in Figure 1) during 2003, compared to 2001, 2002, or 2004 [Sutherland and Pickart, 2002]; and (3) warm waters of Irminger Current origin were present at depth in Kangerdlugssuaq fjord during 2004 [Christoffersen et al., 2008], when there was a positive SSTA at the coast north of Ikertivaq (Figure 7).
 Thus, following high air temperatures in winter 2002–2003, summer 2003 had anomalously high ocean and fjord water temperatures (Figures 5a, 7, and 9). We propose that this warm water reduced fjord ice and the presence of the mélange during winters 2003–2004 and 2004–2005. For example, Landsat imagery (row 14, path 231) shows water in Sermilik Fjord close to Helheim glacier's front in mid-April/early-May 2004 and 2005, whereas in 2003 the mélange was solid at this time, and in 2006 there was extensive fjord ice. We postulate that as a consequence of the warm waters and minimal fjord ice, the speed and calving rate of the glaciers increased, with fastest flow and highest calving rates during 2004 or 2005. During 2004 and 2005, a negative SSTA can be seen at the coast in late summer, albeit weak in 2004 (Figures 5 and 7). This SSTA was well established in summer 2005 (Figures 5 and 7), and cold surface water hugged the coast, marking an apparent recovery of the EGCC. Water temperatures along the coast continued to drop through 2006 (Figure 5e) synchronous with a slowdown of the glaciers. High ocean temperatures occurred offshore in 2007; however, the presence of cold coastal waters (Figure 7) meant there was only minor glacier reactivation.
 Our interpretation of these data is that the dynamics of these glaciers are controlled principally by the temperature of the ocean waters. It is clear that in order for this to occur there must be exchange of waters between the coast and the fjords, with the warm water at the coast entering the fjords and reaching the glacier front margins. This exchange appears to occur on both the west coast of Greenland, with warm water impacting the velocity of Jakobshavn Isbrae [D. M. Holland et al., 2008], and the east coast, where warm waters have been reported in both Kangerdlugssuaq [Christoffersen et al., 2008] and Sermilik [Straneo et al., 2010] fjords. Warm surface water is clearly visible in the Landsat SST at the location of major troughs (e.g., compare Figure 1 and Figure 9), including Helheim and Kangerdlugssuaq, suggesting that warm water is routed toward the coast via these bathymetric features. At Jakobshavn, the arrival of warm water in the fjord required it to overtop the shallow sill at the fjord mouth [D. M. Holland et al., 2008]. While the bathymetry of all of the SE Greenland fjords is not well known, neither Sermilik nor Kangerdlugssuaq fjords have coastal sills [Buch, 2002], so there should be little impediment to the exchange of water between the fjords and the ocean. However, we note that the processes of water circulation within these fjords, their bathymetry, and the subsequent impact of this water on the glacier front and glacier dynamics are poorly constrained and require further research. Undercutting of the calving cliff, melt beneath any floating tongue or mélange, and changes in circulation at the glacier front [Motyka et al., 2003] are likely to be key controls.
5.3. Do the Glaciers Affect the EGCC?
 Having shown a possible connection between coastal waters and glacier dynamics in SE Greenland, we next consider the contribution of these glaciers to the cold freshwaters of the EGCC. It is clear that the 2003–2005 speedup resulted in large volumes of icebergs being calved from these glaciers, most of which will have melted in the fjords or in transport along the coast, thus directly contributing to the coastal EGCC. Unfortunately, there are no ice thickness estimates for most of the glacier catchments, making a robust estimate of the iceberg input to the EGCC difficult. Rignot and Kanagaratnam  estimated the iceberg output from this region as ∼220 km3 at the height of the dynamic event in 2005, an increase of ∼70 km3 discharge over that of 2000. Helheim, where glacier thickness is known from airborne lidar and ice-penetrating radar sensors operated by NASA and the University of Kansas, respectively, discharged ∼50 km3 as icebergs or ice cliff melt during 2005, which was an increase of ∼61% over its discharge in 2000. These figures suggest an estimate of around 130–180 km3 of icebergs calved into the coastal waters from the SE Greenland catchments during 2000 and 200–250 km3 during 2005.
 In addition to the iceberg contribution to the current, we must also consider meltwater runoff from the glaciers and from snowmelted in unglaciated parts of the fjord catchments together with changes in these contributions over time. Although runoff produces less water volume than iceberg calving (Figure 3 and Table 1), the water is produced at the glacier front or runs directly into the fjord and may hence have more impact on the glacier than icebergs that melt within the coastal current. As noted above, the lowest glacial runoff in the time series was recorded in 2003 (∼10.5 km3). After a small increase in 2004 (Figure 3b), runoff in 2005 was almost back to the normal for this period (∼22 km3). By 2006 and 2007, annual runoff from the glaciers was ∼30 km3.
 2004 and 2005 were years of both increasing iceberg calving and increasing ice sheet runoff. Together iceberg melt and runoff must have contributed significant additional cold freshwater to the coastal waters of the EGCC during those years. The volume contribution during summer 2005 from the whole SE Greenland coast was around 220–270 km3, with the availability of this freshwater increasing southward along the coast. We hypothesize that this ice sheet–derived water (icebergs plus meltwater) is the cause of the negative coastal SSTA developed during the later summer months. This cold water is clearly observed in the Landsat SST images, in which Kangerdlugssuaq is seen contributing a plume of cold water into the coastal waters (Figure 9). We further suggest that this water makes a significant contribution to the EGCC, at least later in the summer [cf. Bacon et al., 2002].
 Is the volume of water and ice added by iceberg calving and glacier runoff sufficient to affect the temperature of the EGCC? If we assume the discharge from the ice sheet calculated above occurs evenly distributed over a 100 day period in summer, then we can compare this flux with the total transport in the EGCC, ∼0.8 Sv [Bacon et al., 2002]. This simple calculation suggests ∼3%–4% of total volume of the waters in the EGCC results from iceberg calving and ice sheet runoff. Assuming the ice sheet–derived water is at 0°C and 0 salinity, this flux would reduce the temperature of the EGCC by 0.2°C–0.25°C and salinity by 1–1.4 for the whole of this period. However, much of the discharge is icebergs, which take up a latent heat flux when they melt, cooling their surroundings. Icebergs take about 12–24 days to travel along the coast in the EGCC if it is flowing at 0.5–1.0 m s−1 [Sutherland and Pickart, 2008]. Each km3 of ice at 0°C that melts has the potential to lower a water mass of the volume of the EGCC by ∼0.05°C. If ∼50% of the ice melts in transit and ∼1/5 of the icebergs calved are in transit at any time in the 100 days of summer then the minimum estimate for 2005 of the melting of 50% of 200 km3 of ice will lower the temperature of the EGCC by ∼1°C over the 100 days.
 This calculation is clearly simplistic, ignoring, for example, the likelihood of icebergs being at temperatures below 0°C and the storage of icebergs within the ice mélange. However, it does show the potential for the temperature and salinity of the EGCC to be seasonally and interannually affected by the discharge from these glaciers.
 It seems that ice sheet runoff and iceberg melt can make a significant contribution to the temperature and salinity of the EGCC during summer. The interpretation is further supported by (1) the difference between air and sea surface temperature being greatest in 2005 when iceberg calving rates were highest (Figure 4a); (2) comparison of mooring and SSTA data: lowest temperatures at the former typically occur in late spring (around May) due presumably to sea ice breakup (Figure 5a); subsequent negative SSTA in the EGCC values during August (Figure 7) must be due to runoff and calving; and (3) the coastal positive SSTA started to reduce in 2005 (Figure 5e), which must therefore have resulted from ice sheet sources because there was low coastal sea ice coverage that year (Figure 5c).
5.4. Feedback Between Glaciers and the EGCC
 We propose that the glaciers themselves contributed to their own slowdown in a negative feedback with the waters of the EGCC (Figure 10). Faster flow was initiated when coastal waters were warm, resulting from a weak EGCC at a time of low meltwater runoff and calving. The glaciers sped up, increasing their calving rates while runoff also recovered. This increased ice discharge from the ice sheet delivered additional cold water into the EGCC, contributing to its recovery and acting to stabilize the flow speeds of SE Greenland glaciers. Thus, we suggest that the ice sheet's input to the EGCC provides a negative feedback, which tends to restabilize these sensitive SE Greenland glaciers if their ice discharge increases substantially (Figure 10). However, we also note that there has been an overall increase in temperatures within North Atlantic waters [e.g., Todd et al., 2008] and the Irminger Current [Myers et al., 2007] in recent decades, which might drive a regional trend, or more frequent or larger glacier dynamic events, in response to warm water incursions.
Figure 10. Schematic showing the hypothesized negative feedback from increased iceberg discharge and runoff when the SE Greenland outlet glaciers accelerate or lose additional mass through increased surface melting.
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