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The dynamics of a subglacial salt wedge

Published online by Cambridge University Press:  20 May 2020

Earle A. Wilson*
Affiliation:
Environmental Science and Engineering, California Institute of Technology, Pasadena,CA 91125, USA
Andrew J. Wells
Affiliation:
Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Oxford OX1 3PU, UK
Ian J. Hewitt
Affiliation:
Mathematical Institute, University of Oxford, Oxford OX1 2JD, UK
Claudia Cenedese
Affiliation:
Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
*
Email address for correspondence: earlew@caltech.edu

Abstract

Marine-terminating glaciers, such as those along the coastline of Greenland, often release meltwater into the ocean in the form of subglacial discharge plumes. Though these plumes can dramatically alter the mass loss along the front of a glacier, the conditions surrounding their genesis remain poorly constrained. In particular, little is known about the geometry of subglacial outlets and the extent to which seawater may intrude into them. Here, the latter is addressed by exploring the dynamics of an arrested salt wedge – a steady-state, two-layer flow system where salty water partially intrudes a channel carrying fresh water. Building on existing theory, we formulate a model that predicts the length of a non-entraining salt wedge as a function of the Froude number, the slope of the channel and coefficients for interfacial and wall drag. In conjunction, a series of laboratory experiments were conducted to observe a salt wedge within a rectangular channel. For experiments conducted with laminar flow (Reynolds number $Re<800$), good agreement with theoretical predictions are obtained when the drag coefficients are modelled as being inversely proportional to $Re$. However, for fully turbulent flows on geophysical scales, these drag coefficients are expected to asymptote toward finite values. Adopting reasonable drag coefficient estimates for this flow regime, our theoretical model suggests that typical subglacial channels may permit seawater intrusions of the order of several kilometres. While crude, these results indicate that the ocean has a strong tendency to penetrate subglacial channels and potentially undercut the face of marine-terminating glaciers.

Type
JFM Papers
Copyright
© The Author(s), 2020. Published by Cambridge University Press

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