1 Introduction
Ocean currents are a major factor in the movement of suspended material over large distances along ocean basins. The conveyance of suspended material by currents as a main transport mechanism is critical for ecosystems as they determine the connectivity of some marine populations inhabiting the benthic or pelagic environments (e.g., Bryan-Brown et al., 2017; Sanvicente-Añorve et al., 2014, 2018). Ocean currents also transport contaminant materials derived from anthropogenic activities (Dow, 1999; Pohl et al., 2020; Zaborska et al., 2017), eventually reaching the coast, accumulating in remote places, or sinking to the ocean bottom. Considering the importance of currents in transporting living and non-living suspended material, it is crucial to understand their kinematics. For the Tropical Atlantic, different authors have described the surface currents (Johns et al., 2014; Lumpkin & Garzoli, 2005; Müller-Karger et al., 1989), while others have characterized the climatological surface currents from the western tropical Atlantic to the Gulf of Mexico (GoM) (Andrade & Barton, 2000; Gordon, 1967; Johns et al., 2002; Muller-Karger et al., 1988, 1995; Romanou et al., 2004; Zavala-Hidalgo et al., 2014). Recently, studies have focused on understanding the sargassum transport routes from the Equatorial Atlantic through the Caribbean Sea (CS) and into the GoM (Athié et al., 2020; Beron-Vera et al., 2022; Orfila et al., 2021; Ortiz-Royero et al., 2013; Otero et al., 2016; Putman et al., 2018, 2020). This is due to the emergence of a new sargassum generation area in the tropical Atlantic (Gower et al., 2013; Wang & Hu, 2017), resulting in substantial environmental, social, and economic effects across the Caribbean region. Besides sargassum, understanding the currents system from Equatorial Atlantic to the GoM is relevant for plastics (Law et al., 2010), nutrients (Williams & Follows, 2003), and organisms (Sanvicente-Añorve et al., 2019), as the results indicate the fundamental role of the North Brazil and Guyana currents (Johns et al., 2014), establishing the connectivity between the western Atlantic and the Caribbean (Andrade-Canto & Beron-Vera, 2022; Muller-Karger et al., 1988, 1995).
The Equatorial Atlantic to the GoM currents system has a clear seasonal variability. During the summer and fall, a significant part of the North Brazil Current (NBC) retroflects and merges into the eastward-flowing North Equatorial Countercurrent (NEC), which then intensifies. In spring, the NEC weakens and superficially reverses. In some cases, the NBC and the western boundary current to the north intensify simultaneously, forming part of the North Atlantic large-scale gyre moving northwestward to the CS (Garzoli et al., 2003; Johns et al., 2003). The current dynamics in the CS are dominated by a primary jet that forms the Caribbean Current (CC) as water is transported through the southern region of the Lesser Antilles by a boundary current along the South American coasts (Rhein et al., 2005), continuing to flow northwestward through the CS on to the Yucatan Channel. The southern CS has small recirculation gyres off Panama and south of the Yucatan Channel interacting with the bathymetry, while the slower northern jet is dominated by mesoscale anticyclones (Chérubin & Richardson, 2007). In addition to ocean currents, atmospheric forcing influences surface transport, partly determining the trajectory of near-surface material (Johns et al., 2020; Müller-Karger et al., 1989; Putman et al., 2018). The atmospheric variability in the region is dominated mainly by the easterly winds, which in turn are modulated by the Intertropical Convergence Zone (ITCZ) migration, cold fronts’ arrival, and the Caribbean Low-Level Jet (CLLJ) variability. This atmospheric dynamic results in two climatic seasons, a windier and drier season from December to March and the wet season from August to November, regulated by the location of the ITCZ. May-June and September-October are considered a transition period between seasons since easterlies tend to weaken, coinciding with the intensification and bi-modal variability of the CLLJ (García-Martínez & Bollasina, 2020; Hidalgo et al., 2015; Orfila et al., 2021).
While the mentioned studies characterize the ocean currents system or the atmospheric variability in the region, the interaction of wind, waves, and surface currents dictate transport routes of floating matter in the ocean’s surface layer. As such, this study aims to characterize sea-surface current patterns and assess the effect of surface currents and wind interaction on the displacement of floating particles. We utilized Self-Organizing Maps (SOMs) and climatological Lagrangian Coherent Structures (cLCS) to identify the primary transport routes and transport barriers in the region stretching from the western tropical Atlantic to the Central Subtropical Atlantic, including the entrance to the GoM and the Yucatan Peninsula (YP). We used synthetic surface drifters to compute the probability of arrival at select locations within the CS with an emphasis on the eastern coast of the YP, where we also included the effect of wind over the drifters. The results show how the windage plays a key role in advecting particles to some areas along the CS but also provide insight into using SOMs to represent climatological conditions for particle dispersal. This paper is organized as follows: section two describes the data and methods; section three presents the results, describing preferential routes for different combinations of wind and currents, persistent attraction zones and transport barriers, and the modulation of transport barriers by the wind. We summarize our main findings in section four.