Impact of a Localized Source of Subglacial Discharge on the Heat Flux and Submarine Melting of a Tidewater Glacier: A Laboratory Study

Abstract

Idealized laboratory experiments have been conducted in a two-layer stratified fluid to investigate the leading-order dynamics that control submarine melting and meltwater export near a vertical ice-ocean interface as a function of subglacial discharge. In summer, the discharge of surface runoff at the base of a glacier (subglacial discharge) generates strong buoyant plumes that rise along the glacier front entraining ambient water along the way. The entrainment enhances the heat transport toward the glacier front and hence the submarine melt rate increases with the subglacial discharge rate. In the laboratory, the effect of subglacial discharge is simulated by introducing freshwater at freezing temperature from a point source at the base of an ice block representing the glacier. The circulation pattern observed both with and without subglacial discharge resembles those observed in previous observational and numerical studies. Buoyant plumes rise vertically until they find either their neutrally buoyant level or the free surface. Hence, the meltwater can deposit within the interior of the water column and not entirely at the free surface, as confirmed by field observations. The heat budget in the tank, calculated following a new framework, gives estimates of submarine melt rate that increase with the subglacial discharge and are in agreement with the directly measured submarine melting. This laboratory study provides the first direct measurements of submarine melt rates for different subglacial discharges, and the results are consistent with the predictions of previous theoretical and numerical studies.

Nonlinear response of iceberg side melting to ocean currents

“…For tidewater glaciers it has been argued that increasing the strength (buoyancy flux) of the melt plume by supplying subglacial discharge enhances melting of the glacier face, as stronger (faster/wider) plumes entrain more warm ambient water and draw it toward the ice front [ Cenedese and Gatto , ; McConnochie and Kerr , ]. However, in the case of icebergs it is possible to detach this melt plume entirely, allowing the ice to come directly in contact with the warm ambient waters, which are consistently renewed by the advecting background flow.…”

The dynamics of a subglacial salt wedge

“…This is in large part due to the inaccessibility of subglacial channels and the glacier-ocean interface in general. Recent modelling work suggests the submarine melt rate along a glacier's front is sensitive to the spatial distribution of subglacial meltwater outlets (Carroll et al 2016;Cenedese & Gatto 2016). Notably, Slater et al (2015) demonstrates that a distributed line plume can produce up to five times as much melting as a single point source with the same volume flux.…”

Testing a common ice‐ocean parameterization with laboratory experiments

“…Recently, laboratory experiments have been conducted that examine the interaction of a vertical ice wall with cold salty water. One series of experiments has investigated ice‐ocean interactions in a two‐layer stratification that is representative of a Greenland fjord [ Sciascia et al ., ; Cenedese and Gatto , ]. The effects of a fjord‐scale circulation [ Sciascia et al ., ], the distance between two subglaical discharge sources [ Cenedese and Gatto , ], and the strength of a subglacial discharge flux [ Cenedese and Gatto , ] on the melt rate of an ice block have been investigated in this two‐layer environment.…”

“…One series of experiments has investigated ice‐ocean interactions in a two‐layer stratification that is representative of a Greenland fjord [ Sciascia et al ., ; Cenedese and Gatto , ]. The effects of a fjord‐scale circulation [ Sciascia et al ., ], the distance between two subglaical discharge sources [ Cenedese and Gatto , ], and the strength of a subglacial discharge flux [ Cenedese and Gatto , ] on the melt rate of an ice block have been investigated in this two‐layer environment. A second series of experiments has examined the melt rate and meltwater plume velocity in uniform far‐field conditions including a homogeneous ambient fluid [ Kerr and McConnochie , ; McConnochie and Kerr , ], a uniformly stratified ambient fluid [ McConnochie and Kerr , ], and a homogeneous ambient fluid with an external buoyancy source [ McConnochie and Kerr , ].…”