Abstract
Glacial fjord circulation modulates the connection between
marine-terminating glaciers and the ocean currents offshore. These
fjords exhibit a complex 3D circulation with overturning and horizontal
recirculation components, which are both primarily driven by water mass
transformation at the head of the fjord via subglacial discharge plumes
and distributed meltwater plumes. However, little is known about the 3D
circulation in realistic fjord geometries. In this study, we present
high-resolution numerical simulations of three glacial fjords
(Ilulissat, Sermilik, and Kangerdlugssuaq), which exhibit along-fjord
overturning circulations similar to previous studies. However, one
important new phenomenon that deviates from previous results is the
emergence of multiple standing eddies in each of the simulated fjords,
as a result of realistic fjord geometries. These standing eddies are
long-lived, take months to spin up and prefer locations over the widest
regions of deep-water fjords, with some that periodically merge with
other eddies. The residence time of Lagrangian particles within these
eddies are significantly larger than waters outside of the eddies. These
eddies are most significant for two reasons: (1) they account for a
majority of the vorticity dissipation required to balance the vorticity
generated by discharge and meltwater plume entrainment and act to spin
down the overall recirculation; (2) if the eddies prefer locations near
the ice face, their azimuthal velocities can significantly increase melt
rates. Therefore, the existence of standing eddies are an important
factor to consider in glacial fjord circulation and melt rates and
should be taken into account in models and observations.