Melting at the submerged faces of marine-terminating glaciers at the fringes of Antarcticaand Greenland has increased dramatically in recent decades. This acceleration has been
driven in part by the ocean circulation within ice-shelf cavities and fjords through the increased
access of warm, salty water masses and a presumed amplification of the heat flux
towards these glaciers. However, the dynamics of the ocean circulation within fjords and
ice-shelf cavities are poorly understood and require the representation of scales of motion
that range seven orders of magnitude, from 100s of kilometers (circulation on the adjacent
coastal shelves) down to centimeters (at the ice-ocean inner boundary layer interface). This
presents unique challenges for existing models, which underpredict melt rates by an order of
magnitude compared to recent observations at vertical glacial faces.
The work in this dissertation seeks to improve the agreement of models and theory with
observations and provide a better understanding of the dynamical processes within fjords
and ice-shelf cavities. To accomplish this, a series of high-resolution numerical simulations
of increasing complexity is presented. In Chapters 2 and 3, 2- and 3-layer isopycnal model configurations with idealized geometry and forcing are used; subsequently in Chapters 4
and 5, z-coordinate models with idealized and semi-realistic regional configurations are used.
Inspired by the simplest models, theories of the overturning and horizontal recirculation (the
two primary bulk measures of circulation strength within fjords and ice-shelf cavities,) are
developed and tested and used to make predictions for the glacial melt rate. These theories
are then tested in increasingly complex models, which reveal new features and factors that
also should be taken into account. Three important features presented in this dissertation
include the identification of cavity/fjord geometry as a critical constraint on heat transport,
melt-circulation feedbacks in fjords, and the existence of standing eddies, which can both
further amplify glacial melt rates.
This work advances the understanding of the dynamics within fjords and ice-shelf cavities
and many promising avenues of future work have emerged as a result. Future work will likely
continue to provide critical improvements to our understanding of ocean circulation near the
margins of ice sheets and improve our projections of future sea level rise and glacial retreat
in a changing climate.