Structure and dynamics of a subglacial discharge plume in a G reenlandic fjord

Abstract

Discharge of surface‐derived meltwater at the submerged base of Greenland's marine‐terminating glaciers creates subglacial discharge plumes that rise along the glacier/ocean interface. These plumes impact submarine melting, calving, and fjord circulation. Observations of plume properties and dynamics are challenging due to their proximity to the calving edge of glaciers. Therefore, to date information on these plumes has been largely derived from models. Here we present temperature, salinity, and velocity data collected in a plume that surfaced at the edge of Saqqarliup Sermia, a midsized Greenlandic glacier. The plume is associated with a narrow core of rising waters approximately 20 m in diameter at the ice edge that spreads to a 200 m by 300 m plume pool as it reaches the surface, before descending to its equilibrium depth. Volume flux estimates indicate that the plume is primarily driven by subglacial discharge and that this has been diluted in a ratio of 1:10 by the time the plume reaches the surface. While highly uncertain, meltwater fluxes are likely 2 orders of magnitude smaller than the subglacial discharge flux. The overall plume characteristics agree with those predicted by theoretical plume models for a convection‐driven plume with limited influence from submarine melting.

Glacier Calving in Greenland

“…[30,59,61,68,81,85]). Exciting new opportunities have been created by the advent of remotely controlled or autonomous vehicles [86,87]. Additional focused effort is required to achieve the important goal of predicting dynamic ice losses from the whole Greenland Ice Sheet, and hence their future contribution to sea-level rise.…”

Roughness of a subglacial conduit under Hansbreen, Svalbard

“…However, water actually exits glaciers in proglacial streams with average velocities ranging from 1 to 10 m s -1 (Chikita and others, 2010) and likely lower velocities for submarine discharges (e.g. Mankoff and others, 2016). The difference between the exit velocities of water from an idealized frictionless system and from actual glaciers indicates that nearly all of the gravitational potential energy available at the surface is dissipated under the glacier.…”

Influence of meltwater on Greenland Ice Sheet dynamics

“…D1 is a particularly frequent calving region in comparison to the rest of the terminus, as observed during our two field campaigns. At times, a turbulent, sediment-rich plume reaches the fjord surface at D1, as observed in satellite images and during subsequent fieldwork in July 2013 [Mankoff et al, 2016]. While exhibiting similarly frequent calving, terminus height, and velocity characteristics as D1, surface plumes have not been observed at D2.…”

“…At present we have limited hydrographic observations within plumes fed by subglacial discharge [Bendtsen et al, 2015;Mankoff, 2016], resulting in most studies of coupled plumeoutlet glacier dynamics relying on time series of plumes reaching the fjord surface from time-lapse cameras [Fried et al, 2015;Schild et al, 2016;Slater et al, 2017a]. Relying on plume surface expression as a measure of subglacial discharge is inadequate for some tidewater glaciers, as plumes do not always reach the surface of a stratified fjord [Stevens et al, 2016b].…”

“…While recent advances have been made in measuring near-ice (<200 m) hydrographic properties in medium-sized Greenland fjords with low calving rates [Chauché et al, 2014;Mankoff, 2016;Stevens et al, 2016b], these measurements are missing for many studies attempting to estimate subglacial melt rate of mediumsided outlet glaciers [Beaird et al, 2015;Fried et al, 2015;Carroll et al, 2016], the few remaining Greenland ice shelves [Johnson et al, 2011;Wilson and Straneo, 2015], and outlet glaciers with the largest ice discharge and deepest fjords (e.g., Jakobshavn Isbrae, Kangerdlugssuaq Glacier, and Helheim Glacier) [Straneo et al, 2012;Jackson et al, 2014;Jackson and Straneo, 2016;Sutherland et al, 2014;Gladish et al, 2015]. The five largest outlet glaciers have significant persistent ice mélange, which further complicates field operations in their abutting fjords .…”