Increasing meltwater discharge from the Nuuk region of the Greenland ice sheet and implications for mass balance (1960–2012)

Abstract

We assess the runoff and surface mass balance (SMB) of the Greenland ice sheet in the Nuuk region (southwest) using output of two regional climate models (RCMs) evaluated by observations. The region encompasses six glaciers that drain into Godthåbsfjord. RCM data (1960–2012) are resampled to a high spatial resolution to include the narrow (relative to the native grid spacing) glacier trunks in the ice mask. Comparing RCM gridded results with automatic weather station (AWS) point measurements reveals that locally models can underestimate ablation and overestimate accumulation by up to tens of per cent. However, comparison with lake discharge indicates that modelled regional runoff totals are more accurate. Model results show that melt and runoff in the Nuuk region have doubled over the past two decades. Regional SMB attained negative values in recent high-melt years. Taking into account frontal ablation of the marine-terminating glaciers, the region lost 10–20 km3 w.e. a–1 in 2010–12. If 2010 melting prevails during the remainder of this century, a low-end estimate of sea-level rise of 5 mm is expected by 2100 from this relatively small section (2.6%) of the ice sheet alone.

Hypsometric amplification and routing moderation of Greenland ice sheet meltwater release

“…Note that observations as well as model results place the elevation at which the climatological mass budget is in balance (SMB + refreezing = 0) around 1800 m a.s.l. for 2009-2015, which is ∼ 250 m higher than reported for the 1990-2011 period, and similar to elevations in the top-ranking years 1995, 1999, 2003, 2007(Van de Wal et al, 2012. Lindbäck et al (2015) delineated the "Kangerlussuaq catchment" by means of hydraulic potential analysis, which is a steady-state proxy for routing of subglacial water (Shreve, 1972).…”

“…Along the land-terminating sectors of the Greenland ice sheet, hundreds of proglacial rivers transport sizeable meltwater fluxes to surrounding seas. Studies of proglacial river discharge were initiated during the 1970s and 1980s in response to the growing interest in Greenland hydropower, but in recent years attention has turned to understanding ice sheet surface mass balance and hydrology (Mernild and Hasholt, 2009;Bartholomew et al, 2011;Rennermalm et al, 2012;Banwell et al, 2013;Van As et al, 2014;Overeem et al, 2015;Smith et al, 2015). Yet still relatively little is known about Greenland ice sheet freshwater discharge in terms of delays imposed by limitations in hydrological efficiency or because of supra-, en-, and subglacial storage.…”

Dynamics of Greenland�s glacial fjords

“…Subglacial discharge is typically estimated with regional climate models (e.g. Mernild and Liston, 2012;Andersen et al, 2010;Van As et al, 2014). A growing number of studies attempt to infer submarine melting from measurements of ocean heat transport.…”

“…Outside of Sermilik Fjord, the velocity component along the principal axis (230 degrees from north) at a point 45 km offshore of the fjord mouth was extracted for an along-shore wind record. Additionally, the Regional Atmospheric Climate Model v2.3, a high resolution climate model forced by atmospheric reanalysis (RACMO2.3; Van As et al, 2014;Noel et al, 2015), was used to estimate runoff that drains into Sermilik Fjord. Its runoff field provides an estimate of the liquid water that leaves the ice sheet (or terrestrial) surface, but it does not take into account storage or transit within the ice sheet.…”

“…Runoff into proglacial fjords is not directly measured but estimated with regional models and reanalyses that often differ significantly (e.g. Mernild et al, 2010;Andersen et al, 2010;Van As et al, 2014). Second, the glacier-driven circulation from these inputs of freshwater is not well understood.…”