Standing Eddies in Glacial Fjords and Their Role in Fjord Circulation and Melt

Glacial fjord circulation modulates the connection between marine-terminating glaciers and the ocean cur-rents 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 de-viates from previous results is the emergence of multiple standing eddies in each of the simulated fjords, as a result of real-istic 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 par-ticles 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 and 2) if the eddies prefer locations near the ice face, their azimuthal velocities can significantly increase melt rates. Therefore, the existence of standing eddies is an important factor to consider in glacial fjord circulation and melt rates and should be taken into account in models and observations.

Automated summary

Glacial fjord circulation plays a crucial role in connecting marine-terminating glaciers with offshore ocean currents. This study presents high-resolution numerical simulations of three glacial fjords and reveals the emergence of multiple long-lived standing eddies in each fjord due to realistic fjord geometries. These eddies are important for balancing vorticity generated by discharge and meltwater plume entrainment, reducing the overall recirculation, and potentially increasing melt rates near the ice face. The existence of standing eddies should be considered in glacial fjord circulation models and observations.