Similarities and differences in circulation beneath the Filchner-Ronne and Ross Ice Shelves: Lagrangian point of view

The two world’s largest ice shelves, the Filchner-Ronne Ice Shelf (FRIS) and the Ross Ice Shelf (RIS) account for half the area of Antarctic ice shelves. They play a key role in transforming water masses on the shelf and forming Antarctic Bottom Water.

The objective of the work was to study the similarities and differences of circulation under the FRIS and RIS using the data of numerical simulation of currents, temperature, and salinity in the Weddell and Ross Seas from the Whole Antarctica Ocean Model (WAOM). The modelling results were used to run the particle-tracking model Parcels for computing Lagrangian particle trajectories. Three Lagrangian characteristics were calculated for FRIS and RIS: (i) Visitation frequency is defined as the percentage of the particles P visited each 2x2 km grid column at least once in a period of modelling (20 y); (2) Representative particle trajectory is the particle trajectory which deviates least from rest of trajectories; (iii) The mean age is the age of particles visited each 2x2 km grid column at least once.

The representative particle trajectories show that anticyclonic circulation beneath the FRIS and RIS is caused by the inflow of High Salinity Shelf Water (HSSW) through troughs off the western coast of the Weddell and Ross Seas. Transformed into ISW water, it flows out through the troughs in these seas. Part of the transformed water under the FRIS flows out through the Filchner Trough between Berkner Island, while water under RIS flows into the Ross Sea in the strait between Roosevelt Island and the shore. The eastern part of RIS is not ventilated by water inflowing from Ross Island. It is slowly ventilated by water entering a trough between Roosevelt Island and the eastern coast of the Ross Sea. Visitation frequency and representative trajectories suggest similar paths for water mass entering RIS in all seasons. Except December-February particles in anticyclonic gyre can return under RIS. Meanwhile, for particles released in January-August, outflows from FRIS took place through both the Ronne and Filchner ice fronts. In the October-December release the outflow through the Ronne ice front essentially exceeds flow through the Filchner depression.