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.