Abstract

Abstract. Improving the ability of regional climate models (RCMs) and ice sheet models (ISMs) to simulate spatiotemporal variations in the mass of the Greenland Ice Sheet (GrIS) is crucial for prediction of future sea level rise. While several studies have examined recent trends in GrIS mass loss, studies focusing on mass variations at sub-annual and sub-basin-wide scales are still lacking. At these scales, processes responsible for mass change are less well understood and modeled, and could potentially play an important role in future GrIS mass change. Here, we examine spatiotemporal variations in mass over the GrIS derived from the Gravity Recovery and Climate Experiment (GRACE) satellites for the January 2003–December 2012 period using a "mascon" approach, with a nominal spatial resolution of 100 km, and a temporal resolution of 10 days. We compare GRACE-estimated mass variations against those simulated by the Modèle Atmosphérique Régionale (MAR) RCM and the Ice Sheet System Model (ISSM). In order to properly compare spatial and temporal variations in GrIS mass from GRACE with model outputs, we find it necessary to spatially and temporally filter model results to reproduce leakage of mass inherent in the GRACE solution. Both modeled and satellite-derived results point to a decline (of −178.9 ± 4.4 and −239.4 ± 7.7 Gt yr−1 respectively) in GrIS mass over the period examined, but the models appear to underestimate the rate of mass loss, especially in areas below 2000 m in elevation, where the majority of recent GrIS mass loss is occurring. On an ice-sheet-wide scale, the timing of the modeled seasonal cycle of cumulative mass (driven by summer mass loss) agrees with the GRACE-derived seasonal cycle, within limits of uncertainty from the GRACE solution. However, on sub-ice-sheet-wide scales, some areas exhibit significant differences in the timing of peaks in the annual cycle of mass change. At these scales, model biases, or processes not accounted for by models related to ice dynamics or hydrology, may lead to the observed differences. This highlights the need for further evaluation of modeled processes at regional and seasonal scales, and further study of ice sheet processes not accounted for, such as the role of subglacial hydrology in variations in glacial flow.

Highlights

  • The Earth’s ice sheets represent substantial reservoirs of water stored in the form of ice, which contribute to fluctuations in global sea level

  • There is a small seasonal cycle in Ice Sheet System Model (ISSM) dynamics driven by the SMB cycle which complements the mass changes from Modèle Atmosphérique Régionale (MAR), with an amplitude roughly an order of magnitude smaller than the SMB fluctuations

  • We have shown that in order to compare spatial and temporal variations in Greenland Ice Sheet (GrIS) mass from regional climate models (RCMs), ice sheet models (ISMs) results, and the Gravity Recovery and Climate Experiment (GRACE)-LM solution, it is necessary to spatially and temporally filter the model outputs

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Summary

Introduction

The Earth’s ice sheets represent substantial reservoirs of water stored in the form of ice, which contribute to fluctuations in global sea level. Alexander et al.: Greenland Ice Sheet seasonal and spatial mass variability. The speed-up of glaciers has been attributed to warming oceans (Rignot et al, 2012) and lubrication of the GrIS bed from meltwater generated at the surface, and channeled from the surface to the bed by vertical conduits, allowing glaciers to slide more (Zwally et al, 2002). This second factor has been shown to be more complex than initially thought, resulting in speed-ups or slow-downs that depend on the volume of meltwater reaching the bed and the time of year (e.g., Sundal et al, 2011)

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