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AbstractAn Empirical Orthogonal Function (EOF) variance analysis was performed to map in detail the spatiotemporal variability in individual stake mass-balances (ba) on Mittivakkat Gletscher (MG) – in a region where at present five out of ~20.000 glaciers have mass-balance observations. The EOF analysis suggested that observed ba was summarized by two modes: EOF1 and EOF2 represented 80% (significant) and 6% (insignificant) of the explained variance, respectively. EOF1 captured a decline in ba that was uniformly distributed in space at all stakes. The decline was correlated with albedo observations and air temperature observations from nearby stations. EOF2, however, described variations in ba that were heterogeneously distributed among stakes and associated with local slope and aspect. Low elevation stakes (~<400 m a.s.l.) showed relatively negative (out of phase) correlation and higher elevated stakes relatively positive (in phase) eigenvector correlation values with EOF2. Such relatively negative and positive eigenvector correlation values were present where the constituted of exposed glacier ice or snow cover, respectively. The results from this study show how EOF analyses can provide information on spatiotemporal patterns of glacier mass-balance. Understanding such detailed variabilities in mass-balance on a Greenlandic glacier is of interest because a fifth of the Arctic contribution from glaciers and ice caps to sea-level rise originates from Greenland.

Large, deep‐keeled icebergs are ubiquitous in Greenland's outlet glacial fjords. Here we use the movement of these icebergs to quantify flow variability in Sermilik Fjord, southeast Greenland, from the ice mélange through the fjord to the shelf. In the ice mélange, a proglacial mixture of sea ice and icebergs, we find that icebergs consistently track the glacier speed, with slightly faster speeds near terminus and episodic increases due to calving events. In the fjord, icebergs accurately capture synoptic circulation driven by both along‐fjord and along‐shelf winds. Recirculation and in‐/out‐fjord variations occur throughout the fjord more frequently than previously reported, suggesting that across‐fjord velocity gradients cannot be ignored. Once on the shelf, icebergs move southeastward in the East Greenland Coastal Current, providing wintertime observations of this freshwater pathway. Iceberg motion reveals flow variability in fjord, mélange, and shelfResidence times of icebergs vary significantly by year and regionIcebergs map out fjord‐scale circulation patterns

AbstractSuspended sediment concentration and transport is modeled for the Mittivakkat Glacier located on Ammassalik Island, South-East Greenland, using a numerical sediment model based on lumped-elements. Empirical equations calculate sediment erosion and deposition within a constant idealized glacier drainage system. The sediment model is forced by observations and an energy balance model based on meteorological observations that provide a simulated Surface Melt and liquid Precipitation available for supra-, en-, sub-, and proglacial flow processes after vertical percolation and potential storage within the snowpack (henceforth SMP) from the glacier surface which is available for subglacial erosion, glaciofluvial transport, and deposition within the drainage system. The idealized drainage system is constrained following the descriptions and conclusions from previous work. A model simulation run for summer 2005 shows that the cumulative modeled suspended sediment transport lies within 3% when compared with observations. Model results show that the temporal changes in the calculated suspended sediment concentrations vary over the melt season in some agreement with measured field data for the summer of 2005. Forcing the sediment model gives a correlation coefficient of 0.89 using observed proglacial meltwater discharge values and the correlation coefficient is 0.63 using modeled supraglacial meltwater runoff. The sediment model successfully captures the observed concentration and transport of suspended sediment which indicates a sufficient sediment reservoir available for transport through the idealized drainage system.

AbstractThis study focused on simulated glacier surface conditions (simulated Surface Melt and liquid Precipitation available for supra-, en-, sub-, and proglacial flow processes [after vertical percolation and potential storage within the snowpack] [henceforth SMP]), internal water storage and release, and runoff from the Kangerlussuaq drainage area of the Greenland Ice Sheet (GrIS), West Greenland, for the period 2006/2007 to 2007/2008. GrIS winter accumulation and summer ablation processes, including SMP, was simulated on both daily and hourly time steps. Using hourly meteorological driving data produced more realistic meteorological conditions instead of daily-averaged data, in relation to snow and melt threshold surface processes, and produced 9–17% higher annual cumulative SMP. The difference between simulated SMP and observed catchment runoff showed a decreasing lag time through the summer, and a drainage system storage buildup through approximately June and early July of up to 0.29 × 109 m3, and a storage release through approximately late July and August of up to 0.25 × 109 m3. The simulated total Kangerlussuaq SMP for 2006/2007 and 2007/2008, indicated a reduction of 30%. This reduction in SMP occurred simultaneously with the reduction in the overall pattern of satellite-derived GrIS surface melt from 2007 to 2008.

ABSTRACTIce-sheet melting is the primary water source for the proglacial Watson River in southern west Greenland. Discharge from the large, approximately 12,000 km2ice-sheet catchment draining through the Watson River has been monitored since 2006. While this record is of respectable length for a Greenland monitoring effort, it is too short to resolve climate signals. Therefore, we use observed Tasersiaq lake discharge and Kangerlussuaq air temperature to reconstruct annual Watson River discharge back to 1949. The resulting sixty-five-year record shows that average ice-sheet runoff since 2003 has roughly increased by 46 percent relative to the 1949–2002 period. The time series suggests that the five top-ranking discharge years occurred since 2003. The three top-ranking discharge years (2010, 2012, and 2016) are characterized by melt seasons that were both long and intense. Interannual variability more than doubled since 2003, which we speculate to be because of hypsometric runoff amplification enhanced by albedo decrease and decreased firn permeability. The reconstructed time series proves to be a valuable tool for long-term evaluation of Greenland Ice Sheet surface mass balance models. A comparison with freshwater fluxes calculated by a downscaled version of the regional climate model RACMO2 reveals high correlation (r = 0.89), and also shows that the model possibly underestimates runoff by up to 26 percent in above-average melt years.

ABSTRACTNew measurements of Watson River sediment and solute concentrations and an extended river discharge record improved by acoustic Doppler current profiler (ADCP) measurements are used to calculate the total sediment and solute transport from a large ice-sheet sector in southern west Greenland. For the 2006–2016 period, the mean annual sediment and solute transport was 17.5 ± 7.2 × 106 t and 85 ± 30 × 103 t, respectively (standard deviation given). The highest annual transport occurred in 2010, attaining values of 29.6 × 106 t and 138 × 103 t, respectively. The corresponding annual average values of specific transport are 1.39 × 103 t km−2a−1for sediment and 6.7 t km−2a−1for solutes from the approximately 12,600 km2(95% ice covered) catchment, yielding an area-average erosion rate of 0.5 mm a−1. The specific transport is likely several times higher under the ice sheet near the margin where all meltwater passes than it is in the interior where the ice sheet is frozen to the bed. We conclude that the Greenland Ice Sheet is a large supplier of sediment and solutes to the surrounding fjords and seas. We find that the proglacial area can be a net source of sediments during high floods and we confirm that an increased amount of meltwater-transported sediments can explain the expansion of deltas around Greenland, contradictory to delta erosion observed elsewhere in the Arctic in recent years.

ABSTRACTThe spatiotemporal distribution of freshwater runoff from the Greenland Ice Sheet (GrIS) determines the hydrographic and circulation conditions in Greenlandic fjords. The distribution of GrIS first-order atmospheric forcings, surface mass-balance (SMB), including snow/ice melt, and freshwater river discharge from the Kangerlussuaq drainage catchment were simulated for the thirty-five-year period 1979/1980–2013/2014. ERA-Interim (ERA-I) products, together with the modeling software package SnowModel, were used with relatively high-resolutions of 3-h time steps and 5-km horizontal grid increments. SnowModel simulated and downscaled grid mean annual air temperature (MAAT) and SMB correspond well to point observations along a weather station transect (the K-transect). On average, simulated catchment runoff was, however, overestimated and subsequently adjusted against observed runoff. This overestimation could likely be because of missing multiyear firn processes, such as nonlinear meltwater retention, percolation blocked by ice layers, and refreezing. In the GrIS Kangerlussuaq catchment, the simulated thirty-five-year MAAT was −15.0 ± 1.4°C, with a mean 0° isotherm below 280 m a.s.l. near the ice sheet margin. At the ice sheet margin, on average, 45 percent of precipitation fell as snow. At 2,000 m a.s.l., snow constituted 98 percent of the total precipitation. At the catchment outlet of Watson River draining into the fjord Kangerlussuaq, 80 percent of the simulated runoff originated from GrIS ice melt, 15 percent from snowmelt, and 5 percent from rain.