Impact of Two Plumes’ Interaction on Submarine Melting of Tidewater Glaciers: A Laboratory Study

Abstract

Idealized laboratory experiments investigate the glacier-ocean boundary dynamics near a vertical glacier in a two-layer stratified fluid. Discharge of meltwater runoff at the base of the glacier (subglacial discharge) enhances submarine melting. In the laboratory, the effect of multiple sources of subglacial discharge is simulated by introducing freshwater at freezing temperature from two point sources at the base of an ice block representing the glacier. The buoyant plumes of cold meltwater and subglacial discharge water entrain warm ambient water, rise vertically, and interact within a layer of depth H 2 if the distance between the sources x 0 is smaller than H 2 a/0.35, where a is the entrainment constant. The plume water detaches from the glacier face at the interface between the two layers and/or at the free surface, as confirmed by previous numerical studies and field observations. A plume model is used to explain the observed nonmonotonic dependence of submarine melting on the sources' separation. The distance between the two sources influences the entrainment of warm water in the plumes and consequently the amount of submarine melting and the final location of the meltwater within the water column. Two interacting plumes located very close together are observed to melt approximately half as much as two independent plumes. The inclusion, or parameterization, of the dynamics regulating multiple plumes' interaction is therefore necessary for a correct estimate of submarine melting. Hence, the distribution and number of sources of subglacial discharge may play an important role in glacial melt rates and fjord stratification and circulation.

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

“…Finally, this model does not take into account the contribution of melt water to the plume. This approach has been applied successfully before in a similar setting [ Cenedese and Gatto , ].…”

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

“…The description of the experimental apparatus is similar to that of Cenedese and Gatto (2016). The laboratory experiments were conducted in a rectangular tank, 150 3 15 3 30 cm 3 ( Fig.…”

“…However, the melt rate measured in the laboratory experiments includes both the melt rate due to the plume forced by subglacial discharge, that is, convection-driven melting, and the melting occurring in the region outside the plume due to melt-driven convection. Using plume theory as in Cenedese and Gatto (2016), one can estimate the ratio of the area of the ice block face covered by the plume to the remaining area. This ratio varies with subglacial discharge and ranges from 0.33 to 0.85 for Q sg varying from 0.6 to 3.4 cm 3 s 21 .…”

“…After residual motions in the two-layer system came to a halt, the experiment started. Consistent with the approach taken in previous experiments (Sciascia et al 2014;Cenedese and Gatto 2016), the effect of Earth's rotation was ignored. This choice is justified because, in general, in Greenland alongfjord variations tend to dominate over across-fjord variations, consistent with the fact that many fjords are too narrow for the circulation to be significantly influenced by Earth's rotation (e.g., Straneo et al 2010;Johnson et al 2011;Sutherland et al 2014).…”

“…Not to scale. Adapted from Cenedese and Gatto (2016). extremely slowly in order to reduce the motion in the tank and any mixing between the two layers. After the ice block was secured in place, both the subglacial discharge and the sink pumps were started.…”