  We document the long-term evolution of an Agulhas ring detected from
satellite altimetry using a technique from nonlinear dynamical systems that
enables objective (i.e., observer-independent) eddy framing. Such objectively
detected eddies have Lagrangian (material) boundaries that remain coherent
(unfilamented) over the detection period. The ring preserves a quite compact
material entity for a period of about 2 years even after most initial coherence
is lost within 5 months after detection. We attribute this to the successive
development of short-term coherent material boundaries around the ring. These
boundaries provide effective short-term shielding for the ring, which prevents
a large fraction of the ring's interior from being mixed with the ambient
turbulent flow. We show that such coherence regain events cannot be inferred
from Eulerian analysis. This process is terminated by a ring-splitting event
which marks the ring demise, near the South American coast. The genesis of the
ring is characterized by a ring-merging event away from the Agulhas
retroflection, followed by a 4-month-long partial coherence stage, scenario
that is quite different than a simple current occlusion and subsequent eddy
pinch off.
