Coherent sets in dynamical systems are regions in phase space that optimally “carry mass” with
them under the system’s evolution, so that these regions experience minimal leakage. The dominant
tool for determining coherent sets is the transfer operator, which provides a complete description of
Lagrangian mass transport. In this work, we combine existing transfer operator methods with a
windowing scheme to study the spatial and temporal evolution of a so-called Agulhas ring: a large
anticyclonic mesoscale eddy playing a key role in inter-ocean exchange of climate-relevant properties.
Our focus is on ring decay over time and the windowing scheme enables us to study how the
most coherent region (our estimate of the ring) varies in position and size over a period of more than
two years. We compare the eddy-like structure and its spatio-temporal changes as revealed by our
method and by a classical Eulerian approach.