Increased variability in Greenland Ice Sheet runoff from satellite observations

Abstract

Runoff from the Greenland Ice Sheet has increased over recent decades affecting global sea level, regional ocean circulation, and coastal marine ecosystems, and it now accounts for most of the contemporary mass imbalance. Estimates of runoff are typically derived from regional climate models because satellite records have been limited to assessments of melting extent. Here, we use CryoSat-2 satellite altimetry to produce direct measurements of Greenland’s runoff variability, based on seasonal changes in the ice sheet’s surface elevation. Between 2011 and 2020, Greenland’s ablation zone thinned on average by 1.4 ± 0.4 m each summer and thickened by 0.9 ± 0.4 m each winter. By adjusting for the steady-state divergence of ice, we estimate that runoff was 357 ± 58 Gt/yr on average – in close agreement with regional climate model simulations (root mean square difference of 47 to 60 Gt/yr). As well as being 21 % higher between 2011 and 2020 than over the preceding three decades, runoff is now also 60 % more variable from year-to-year as a consequence of large-scale fluctuations in atmospheric circulation. Because this variability is not captured in global climate model simulations, our satellite record of runoff should help to refine them and improve confidence in their projections.

Solid-phase Mn speciation in suspended particles along meltwater-influenced fjords of West Greenland

“…Glacially-derived metal fluxes are expected to be particularly prominent in glaciated fjords, such as along the coastline of West Greenland, where meltwater is confined, creating strong gradients in turbidity and salinity (Hopwood et al, 2016). Since the annual meltwater flux from the Greenland Ice 4 Sheet is expected to increase in the future due to increasing Arctic air temperatures (Boers and Rypdal, 2021;Slater et al, 2021), glacially-sourced Mn (and Fe) inputs may increase. However, the flux and speciation of Mn, particularly solid-phase Mn, delivered to fjords and adjacent waters are poorly understood.…”

A 30-year monthly 5 km gridded surface elevation time series for the Greenland Ice Sheet from multiple satellite radar altimeters

“…The significant signals of seasonal variation are mainly concentrated in the ablation zone below the equilibrium line identified in McMillan et al (2016). Thinning in autumn (July-August-September) and thickening in spring (January-February-March) are driven by the seasonal fluctuations in surface melting, snowfall, and ice dynamics (Bartholomew et al, 2011;Slater et al, 2021). Between May and August, surface melting and enhanced ice dynamics when the surface meltwater gains access to the ice-bed interface, lubricating basal motion, lower the surface in the ablation zone.…”

Discharge Estimation With Improved Methods Using MODIS Data in Greenland: An Application in the Watson River

“…Discharge changes in the Watson River are closely related to the changes in Greenland's ablation zone, which respond to atmospheric forcing [15] and natural variability of climate (i.e., the climate variability without anthropogenic forcing) [42]. The frequent occurrence of central Pacific El Niño events has slowed down the Greenland summer warming in the past decade [42].…”

“…The dominant high-pressure system led to intensified warm air advection from southern latitudes into west Greenland and more clear-sky conditions, which further enhanced melt-albedo feedbacks [44], [45]. During the two years, the negative phase of the NAO enhanced surface melting and reduced snowfall, especially in west Greenland, resulting in increases in river discharge [15], [43]. Although our results underestimated the high flows in 2012, the estimated discharge captured the high discharge signal in 2019 (See Fig.…”

“…Van Dijk et al [14] combined MODIS data, passive microwave data, ENVISAT and JASON-2 altimetry data to estimate river discharge at a global scale, but rivers in Greenland are not included in their study. Slater et al [15] used CryoSat-2 satellite altimetry to estimate Greenland's total runoff yet the discharge information of an individual river was overlooked due to the large study scale.…”