Delving into the analysis for each zone, we observed certain characteristics in the particles’ spatial distribution associated with the forcings and main currents as defined by cLCS (Table 1; Figure S2 in Supplementary Information and 10):
The most important result of these experiments is the particles’ geographical distribution according to the effect of wind. Zones 1, 4, 5, and 6 are dominated by windage (1% windage), while zones 2, 3, 10, and 9 are dominated by windage and Stokes drift (2% of wind). The distribution of particles can be explained by the persistent presence of the cLCS identifying transport barriers that prevent particles from reaching the coast (Figure 2 and Figure 9). For the particles to cross these barriers, it is necessary for the winds to weaken the cLCS.
The dynamics of surface transport are partially controlled by the inflow into the CS, which according to Johns et al. (2002), can be divided into three main groups of passages: the Greater Antilles (zones 6 and 7), the Leeward Islands (zone 8), and the Windward Islands passages (zone 9), which coincide with the main transport routes identified by the cLCS. The seasonal cycle of the mean currents inflow distribution in the passages connecting the Atlantic Ocean with the CS has an annual and semiannual variability with a maximum in late spring and summer and a minimum in fall, continuing to the Yucatan Channel (Johns et al., 2002). Nevertheless, the NBC is the single largest inflow source (40%) to the Caribbean (Chérubin et al., 2005), which displays a strong mesoscale variability in inter-island passage transports. Chérubin et al. (2005) also found that the current’s maximum velocity position is in phase with the transport variations and independently of its extension. The Lagrangian experiments show that identifying transport pathways and barriers can explain particle displacement distribution, where the wind is a crucial parameter explaining particle intrusion into the Caribbean. Once in the CS, the three westward jets described by Chérubin & Richardson (2007) flow with their speeds decreasing with increasing latitude. These jets and their relation to our results are described below.
  1. The southern and fastest jet is located at ~11.5°N, coinciding with the passage of particles at zone 9 with 2% windage. This southern jet is characterized by southern cyclones, which move northwestward as the anticyclonic CC circulation intensifies.
  2. The center and second fastest jet, at ~14°N, coincides with the particle’s passage through zone 8 without wind or with 1% windage. This center jet flows faster between August and December and is seasonally intensified by the NBC; this coincides with the larger particle density found in the zone during this period when considering low wind influence (1% windage or less). It is important to note that the intensification of the center jet is due to an increase in the mean kinetic energy (negative potential vorticity anomaly) that increases the number of cyclones during the fall. This is observed in the particle’s trajectory once they enter the CS.
  3. The northern and slowest jet is found at ~16.8°N, corresponding to zones 6 and 7. These zones show confluence only without windage (zone 7) and 1% windage (zone 6). This area is dominated by mesoscale anticyclones, sustaining westward currents south of Puerto Rico and Hispañola (Baums et al., 2006), so particles remain in this area with low wind conditions and are displaced further south only with 2% windage. Therefore, the wind effect in this region is decisive in the particle’s trajectory.
Besides the water inflow and current jets, the Caribbean basin is influenced by atmospheric phenomena such as the easterly waves, anticyclonic cold fronts (also known as Central American Cold Surges), Caribbean Low-Level Jet (CLLJ), the trade winds, and the ITCZ. The easterly waves are wave-type disturbances in the tropical easterly current. These waves are associated with the hurricane season (summer), characterized by a cyclonic circulation that deforms the pressure field, causing the wind direction to change from northeast to the east (Caviedes, 1991). As such, easterly waves could promote particle displacement from the Equatorial Atlantic towards the CS by the windage effect. The arrival of anticyclonic cold fronts typically occurs between September and April and can extend as far south as 10oN latitude (DiMego et al., 1976). These cold fronts are associated with a significant increase in wind intensity, cloud cover, atmospheric pressure, wave height, and a decrease in temperature (Appendini et al., 2014, 2018; Cao et al., 2020; Ortiz-Royero et al., 2013). Considering the strong northerly wind component during cold fronts, they could influence the particle transport by displacing them towards the south, impending them to reach areas such as the Yucatan Peninsula. The Caribbean Low-Level Jet (CLLJ) is a near-surface branch of the easterlies that intensifies seasonally and has a nearly east-west direction (García-Martínez & Bollasina, 2020; Hidalgo et al., 2015). The Caribbean Counter Current (CCC) is controlled by the CLLJ, which during relatively mild wind conditions, promotes the intensification of the Panama-Colombia Gyre (Orfila et al., 2021). While the CLLJ can promote windage displacing particles towards the west, during its relaxation phase, the particle displacement into the CCC and the Panama-Colombia Gyre could be expected. Finally, the trade winds’ seasonality and the ITCZ’s consequent latitudinal displacement (Aliaga Nestares et al., 2022; Haffke et al., 2016; Henke et al., 2012; Skliris et al., 2022) likely influence the currents and particularly the windage effect on particle transport.