Historical ablation rates on south-east Greenland glaciers measured in the 1933 warm summer

Ice ablation rates measured on four glaciers in south-east Greenland in summer 1933 are recovered from an old field book of geologist K. Milthers. These unpublished ablation data are among the first measured in Greenland and were obtained during a warm period comparable to that of recent years. Ablation rates of up to 45 mm ice eq. d−1 were observed. Using the Tasiilaq meteorological record, we calculate degree-day factors of ca. 3–5 mm ice eq. d−1°C−1. Comparing these results with 1996–2012 observations at one of Milthers’ glaciers (Mittivakkat), we find that ablation rates and degree-day factors are significantly higher (61±50%) in recent years. We speculate this to be due to a reduction in surface albedo, and perhaps the retreat of the glaciers out of the cold maritime inversion layer. Our findings suggest that using a temperature-index method that assumes constant degree-day factors may produce inaccurate long-term ablation estimates for south-east Greenland glaciers, further emphasizing the value of the rare 1933 measurements for validation of ablation models

GPS based surface displacements – a proxy for discharge and sediment transport from the Greenland Ice Sheet

Abstract. The elastic respond of the Earth's surface to mass changes has been measured with Global Positioning System (GPS). Mass loss as accumulated runoff and sediment transport from a 10 000 km2 segment of the Greenland Ice Sheet (GrIS) correlated very well (R2 = 0.83) with GPS measured uplift. Accumulated winter precipitation correlated fairly well with surface depression (R2 = 0.69). The relationships are based on seven years of runoff and sediment transport observations from the Watson River (2007–2013), winter precipitation from Kangerlussuaq Airport and GPS observations at Kellyville. GPS recordings of surface subsidence and uplift from 1996–2013 are used to calculate 18 years time series of annual runoff, sediment and solute transport and winter precipitation. Runoff and related transport of sediment and solutes increase over the period, while winter precipitation (land depression) tends to decrease. Based on the entire GPS record (1996–2013), it is shown that until 2005–2006 the mass balance of this segment of the GrIS was rather stable – since then there has been an increasing loss of mass, culminating in 2012. </jats:p

Ferskvandsafstrømning - fra Østgrønland i en tid med klimaforandringer

Danske forskningsstationer i &Oslash;stgr&oslash;nland&nbsp;bidrager med nyttig viden&nbsp;til bestemmelsen af klimaets effekt&nbsp;p&aring; ferskvandsafstr&oslash;mningen fra&nbsp;&Oslash;stgr&oslash;nland inklusive Indlandsisen.&nbsp;En ferskvandsm&aelig;ngde, der samlet&nbsp;set forventes at stige med 50 % i&nbsp;fremtiden (2071&ndash;2100)

River inundation suggests ice-sheet runoff retention

AbstractThe Greenland ice sheet is experiencing dramatic melt that is likely to continue with rapid Arctic warming. However, the proportion of meltwater stored before reaching the global ocean remains difficult to quantify. We use NASA MODIS surface reflectance data to estimate river discharge from two West Greenland rivers – the Watson River near Kangerlussuaq and the Naujat Kuat River near Nuuk – over the summers of 2000–12. By comparison with in situ river discharge observations, ‘inundation–discharge’ relations were constructed for both rivers. MODIS-based total annual discharges agree well with total discharge estimated from in situ observations (86% of summer discharge in 2009 to 96% in 2011 at the Watson River, and 106% of total discharge in 2011 to 104% in 2012 at the Naujat Kuat River). We find, however, that a time-lapse camera, deployed at the Watson River in summer 2012, better captures the variations in observed discharge, benefiting from fewer data gaps due to clouds. The MODIS-derived estimates indicate that summer discharge has not significantly increased over the last decade, despite a strong warming trend. Also, meltwater runoff estimates derived from the regional climate model RACMO2/GR for the drainage basins are higher than our reconstructions of river discharge. These results provide indirect evidence for a considerable component of water storage within the glacio-hydrological system.</jats:p

Climate, river discharge and suspended sediment transport in the Zackenberg River drainage basin and Young Sound/Tyrolerfjord, Northeast Greenland, 1995−2003

Climate control on river discharge, suspended sediment transport and conductivity was investigated based on high-resolution time series (1995–2003) from a High Arctic drainage basin at Zackenberg, Northeast Greenland. Data from the Zackenberg River drainage basin (512 km2) was extrapolated to estimate the total transport from land of freshwater, sediments and organic matter to the Young Sound/Tyrolerfjord system (3,016 km2). During the investigation period, a 14-day increase in thawing period, a 50-day decrease in snow cover period, an increasing release of meltwater from exposed glacier surfaces and an increasing annual runoff were recorded. The total annual runoff from the Zackenberg River drainage basin ranges between 122 and 306 million m3 (239–598 mm yr-1), while the total annual runoff to the entire Young Sound/Tyrolerfjord system ranges between 630 and 1,570 million m3 yr-1. Suspended sediment discharges from the Zackenberg River drainage basin and the entire catchment area to Young Sound/Tyrolerfjord are 15,000–130,000 t yr-1 and 77,000–670,000 t yr-1, respectively. For organic matter yield the ranges are, respectively, 1,100–11,500 t yr-1 and 6,000–59,000 t yr-1. In 2003 the total transport of carbon was 1,180 t yr-1 and 6,000 t yr-1 and of nitrate 13 t yr-1 and 66 t yr-1, respectively, for the Zackenberg River drainage basin and the entire catchment area to Young Sound/Tyrolerfjord

Hypsometric amplification and routing moderation of Greenland ice sheet meltwater release

Concurrent ice sheet surface runoff and proglacial discharge monitoring are essential for understanding Greenland ice sheet meltwater release. We use an updated, well-constrained river discharge time series from the Watson River in southwest Greenland, with an accurate, observation-based ice sheet surface mass balance model of the  ∼  12 000 km² ice sheet area feeding the river. For the 2006–2015 decade, we find a large range of a factor of 3 in interannual variability in discharge. The amount of discharge is amplified  ∼  56 % by the ice sheet's hypsometry, i.e., area increase with elevation. A good match between river discharge and ice sheet surface meltwater production is found after introducing elevation-dependent transit delays that moderate diurnal variability in meltwater release by a factor of 10–20. The routing lag time increases with ice sheet elevation and attains values in excess of 1 week for the upper reaches of the runoff area at  ∼  1800 m above sea level. These multi-day routing delays ensure that the highest proglacial discharge levels and thus overbank flooding events are more likely to occur after multi-day melt episodes. Finally, for the Watson River ice sheet catchment, we find no evidence of meltwater storage in or release from the en- and subglacial environments in quantities exceeding our methodological uncertainty, based on the good match between ice sheet runoff and proglacial discharge