  By analyzing a time-homogeneous Markov chain constructed using trajectories
of undrogued drifting buoys from the NOAA's Global Drifter Program, we find
that probability density can distribute in a manner that resembles very closely
the recently observed recurrent belt of high Sargassum density in the tropical
Atlantic between 5--10$^{\circ}$N, coined the \emph{Great Atlantic Sargassum
Belt} (\emph{GASB}). A spectral analysis of the associated transition matrix
further unveils a forward attracting almost-invariant set in the northwestern
Gulf of Mexico with a corresponding basin of attraction disconnected from the
Sargasso Sea, but including the nutrient-rich regions around the Amazon and
Orinoco rivers mouths and also the upwelling system off the northern coast of
west Africa. This represents a data-based inference of potential remote sources
of Sargassum recurrently invading the Intra-Americas Seas (IAS). By further
applying Transition Path Theory (TPT) on the data-derived Markov chain model,
two potential pathways for Sargassum into the IAS from the upwelling system off
the coast of Africa are revealed. One TPT-inferred pathway takes place along
the GASB. The second pathway is more southern and slower, first going through
the Gulf of Guinea, then across the tropical Atlantic toward the mouth of the
Amazon River, and finally along the northeastern South American margin. The
existence of such a southern TPT-inferred pathway may have consequences for
bloom stimulation by nutrients from river runoff.
