Representing Greenland ice sheet freshwater fluxes in climate models

Abstract

Here we present a long‐term (1850–2200) best estimate of Greenland ice sheet (GrIS) freshwater runoff that improves spatial detail of runoff locations and temporal resolution. Ice discharge is taken from observations since 2000 and assumed constant in time. Surface meltwater runoff is retrieved from regional climate model output for the recent past and parameterized for the future based on significant correlations between runoff and midtropospheric (500 hPa) summer temperature changes over the GrIS. The simplicity of this approach enables assimilation of meltwater runoff into coupled climate models, which is demonstrated here in a case study with the medium‐resolution (1°) Community Earth System Model. The model results suggest that the decrease in Atlantic Meridional Overturning Circulation (AMOC) is dominated by warming of the surface ocean and enhanced GrIS freshwater forcing leads to a slightly enhanced (−1.2 sverdrup in the 21st century) weakening of the AMOC.

High-resolution ice sheet surface mass-balance and spatiotemporal runoff simulations: Kangerlussuaq, west Greenland

“…From 2009 to 2012, freshwater runoff has been estimated to explain approximately two-thirds of the mass loss of the GrIS (Enderlin et al 2014). Since the mid-twentieth century, the freshwater runoff from Greenland, including GrIS, has shown a pronounced increase Hanna et al 2013;Lenaerts et al 2015), with the greatest increases in the southern and southwestern parts of Greenland . Specifically, Bamber et al (2012) stated that since 1992 the total runoff from the GrIS changed by 16.9 ± 1.8 km 3 yr −2 .…”

Observed sediment and solute transport from the Kangerlussuaq sector of the Greenland Ice Sheet (2006–2016)

“…Because of the relatively low chemical reactivity of the local gneissic lithology and the low input of marine-derived salts, the estimated ion exports from the GrIS should be regarded as conservative estimates. In Table 4, we present past, present, and future estimates of ion export from the GrIS, based on GrIS runoff modeling estimates derived by Lenaerts et al (2015). The GrIS runoff was calculated from the estimated total freshwater runoff subtracted by solid-ice calving (520 Gt yr −1 ) and seasonal snowmelt from the tundra (50 Gt yr…”

“…), assuming that the contributions from both solid-ice calving and seasonal snowmelt from the tundra remain constant through time (Lenaerts et al 2015). Between the periods 1960-1989 and 2006-2016, the runoff from the GrIS has increased by 65 percent.…”

“…Assuming that runoff is the dominant control on solute export , this increase in runoff is equivalent to a 65 percent increase in solute export. For estimations of future solute exports, the climate-change scenario Representative Concentration Pathways 2.6 (RCP2.6) is applied to present an increasing atmospheric temperature (c. 2 K) over Greenland until the year 2100, followed by a slow decrease (Lenaerts et al 2015). In contrast, the climate-change scenario RCP8.5/4xCO 2 represents a situation with increasing atmospheric CO 2 concentration to four times the preindustrial level in 2120 (c. 5 K in 2100), followed by a stable atmospheric CO 2 concentration (Lenaerts et al 2015).…”

Dynamics of Greenland�s glacial fjords

“…The Greenland Ice Sheet is a growing source of freshwater to the polar ocean (Bamber et al, 2012) that could potentially alter coastal currents and eventually the meridional overturning circulation (Weijer et al, 2012;Lenaerts et al, 2015). In addition to providing buoyancy forcing and a net freshening, the input of meltwater at depth drives upwelling of heat and nutrients around the margins of the ice sheet (Jenkins, 1999;Cottier et al, 2010;Beaird et al, 2015).…”