Figure
4. Lagrangian experiments results. The maps show the annual accumulated
particle density using the HYCOM climatology, without wind, and
according to the release month. The annual accumulated particle density
refers to the number of steps the particles take during a year. The
black line is the coastline, and the gray line is the 200 m isobath.
The Lagrangian experiments were also performed using the spatial
patterns identified by the SOMs analysis with the temporal evolution
given by the BMUs (Figure 3) as the surface current velocity. The
results (Figure 5) show that the SOMs’ pathways and distribution of
particles are similar to those from the HyCOM climatology. A difference
between both datasets is that the velocity from the spatial SOMs remains
stationary according to the BMUs time series (Figure 3). However, the
differences in the distribution of particles are not significant, as we
will describe in section 3.2.3. The SOMs Lagrangian results show that
when particles are released between May and September, their
accumulation in the CS is minimal (<300 particles). Starting
in June, the NERR intensifies, the NBC moves eastward (Condie, 1991),
and the cLCS intensifies at the coasts of Brazil, Suriname, the French
Guiana, and the Lesser Antilles region.
On the other hand, the particles released in October-December show the
effect of the NERR intensification and of the cLCS as transport
barriers, which cause the particles to drift northward along the NEC
toward the Sargasso Sea, and promote a large accumulation of particles
from the Equatorial Atlantic to the north of the Dominican Republic.
This could be associated with NBC rings that stall and decay east of the
Lesser Antilles (between 14°N and 18°N) during these months, as
described by Chérubin & Richardson (2007), and which could displace the
particles to the northern part of the eastern CS and merging with inflow
from the NEC. Between January and April, the NEA, the eastern CS, the
Greater Antilles, and the Bahamas show the largest accumulation of
particles. It should be noted that during this period, the cLCS in the
Lesser Antilles and the Yucatan Channel are intensified, acting as
transport channels that carry particles into the CS and the GoM,
respectively.
Regardless of using the HYCOM climatology or the SOMs-derived velocities
used in the Lagrangian experiments, the particle trajectories show paths
following the strongest currents and the spatial distribution of cLCS.
Those paths create specific accumulation regions, particularly the NEA
and the Lesser and Greater Antilles. However, these results do not
consider wind as an additional forcing (e.g., windage), despite being
one of the most critical factors determining the dynamics at the ocean
surface, as we will analyze in the following experiments.