Complex Greenland outlet glacier flow captured

Abstract

The Greenland Ice Sheet is losing mass at an accelerating rate due to increased surface melt and flow acceleration in outlet glaciers. Quantifying future dynamic contributions to sea level requires accurate portrayal of outlet glaciers in ice sheet simulations, but to date poor knowledge of subglacial topography and limited model resolution have prevented reproduction of complex spatial patterns of outlet flow. Here we combine a high-resolution ice-sheet model coupled to uniformly applied models of subglacial hydrology and basal sliding, and a new subglacial topography data set to simulate the flow of the Greenland Ice Sheet. Flow patterns of many outlet glaciers are well captured, illustrating fundamental commonalities in outlet glacier flow and highlighting the importance of efforts to map subglacial topography. Success in reproducing present day flow patterns shows the potential for prognostic modelling of ice sheets without the need for spatially varying parameters with uncertain time evolution.

Figure 1. Surface speeds for Greenland for 2008–2009.

(a) Observed speeds, adjusted to represent annual averages. (b) Calibrated model speeds at 600-m grid resolution. Coloured dots indicate Pearson's r correlation coefficient and the dotted grey vertical line indicates the median value (0.88). (c–f) Inset showing simulated surface speeds of Jakobshavn Isbræ (c), Kong Oscar Gletscher (d), Kangerdlugssuaq Gletscher (e) and Køge Bugt (f). White lines indacte the position of the profile. Speeds are masked where observed ice thicknesses are <50 m.

Figure 2. Outlet glacier profiles as a function of grid resolution.

(a) Linear regression analysis of the root mean square (r.m.s.) difference χ under grid refinement. Dots mark total χ, and solid and dashed lines indicate statistically significant and not significant trends, respectively. Also, the trends of all glaciers, all ‘isbræ'-type, and all ‘ice-stream' type glaciers are shown. (b–e) Four examples of observed and simulated surface velocity cross profiles, evaluated every 250 m along profiles using bilinear interpolation; Jakobshavn Isbrae (JIB) (b), a glacier that has a high correlation coefficient (Kong Oscar Gletscher) (c), the glacier whose correlation coefficient represents the sample median (Kangerdlugssuaq Gletscher) (d) and a glacier with a poor fit (Køge Bugt S) (e). The shaded grey area indicates observational uncertainty.

Figure 3. Simulated surface speeds for the northwest coast of Greenland.

(a) Overview. (b) 600-m grid resolution and MO2014 subglacial topography. (c) 4,500-m grid resolution and MO2014 subglacial topography. (d) 600-m grid resolution and BA2001 bed topography. (e) 4,500-m grid resolution and BA2001 subglacial topography. Background: shaded relief of the respective subglacial topography.