Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

Abstract

Purpose of the Review This review discusses the role that meltwater plays within the Greenland ice sheet system. The ice sheet's hydrology is important because it affects mass balance through its impact on meltwater runoff processes and ice dynamics. The review considers recent advances in our understanding of the storage and routing of water through the supraglacial, englacial, and subglacial components of the system and their implications for the ice sheet. Recent Findings There have been dramatic increases in surface meltwater generation and runoff since the early 1990s, both due to increased air temperatures and decreasing surface albedo. Processes in the subglacial drainage system have similarities to valley glaciers and in a warming climate, the efficiency of meltwater routing to the ice sheet margin is likely to increase. The behaviour of the subglacial drainage system appears to limit the impact of increased surface melt on annual rates of ice motion, in sections of the ice sheet that terminate on land, while the large volumes of meltwater routed subglacially deliver significant volumes of sediment and nutrients to downstream ecosystems. Summary Considerable advances have been made recently in our understanding of Greenland ice sheet hydrology and its wider influences. Nevertheless, critical gaps persist both in our understanding of hydrology-dynamics coupling, notably at tidewater glaciers, and in runoff processes which ensure that projecting Greenland's future mass balance remains challenging.

Modelling seasonal meltwater forcing of the velocity of land-terminating margins of the Greenland Ice Sheet

“…Additional data and theory will be necessary to address these issues. Together, the models also form a quantitative test of the hypothesis proposed by numerous authors (e.g Chandler et al, 2013;Cowton et al, 2013;Colgan et al, 2011;Hewitt, 2013;Hoffman et al, 2011;Schoof, 2010;van de Wal et al, 2015;Nienow et al, 2017) that the summer acceleration of the GrIS margin is controlled by the evolution of the subglacial hydrological system in a manner analogous to the seasonal speedup of alpine glaciers. The key result of this paper is quantitative support in favour of this hypothesis.…”

“…Under this limit, channelization has a similar impact at high elevations as in the ablation zone. Velocity measurements near the vicinity of a lake hydrofracture at approximately 1450 m elevation suggest that channelization occurs even at high elevations (Bartholomew et al, 2012;Nienow et al, 2017). Winter velocities in this limit will decrease until they hit a lower bound where flow is purely deformational, with no contribution from basal sliding.…”

Long‐Term Support of an Active Subglacial Hydrologic System in Southeast Greenland by Firn Aquifers

“…The behavior of the subglacial hydrologic system at inland locations is incompletely understood (Nienow et al, 2017). Observations in western Greenland show clear year-to-year variations in summer ice velocities (Bartholomew et al, 2011a) without substantial variation in annual local downglacier ice displacement (Tedstone et al, 2015), suggesting sparser subglacial channels and less hydrological efficiency there.…”

Sentinel‐1 Detects Firn Aquifers in the Greenland Ice Sheet

“…Freezing in the shallow firn layer will also limit water access to the deeper firn and increase lateral runoff (Machguth et al, 2016;van Angelen et al, 2013). Mainly through hydrofracture in crevassed areas, aquifers can cause liquid water to flow to the bed of the ice sheet, providing a potential mechanism for aquifer drainage and impacting ice dynamics (Fountain & Walder, 1998;Nienow et al, 2017;Poinar et al, 2017). For example, water at the base of a glacier bed can decrease friction and increase glacier sliding velocity (Fountain & Walder, 1998).…”