Modeling the Exposure of the Macaronesia Islands (NE Atlantic) to Marine Plastic Pollution

Abstract

The constant increase of marine plastic pollution poses an unprecedented risk to oceanic islands, which become increasingly exposed to a hazard of which they have very little control. Located in the Northeast Atlantic Ocean, the Macaronesia is comprised by the Azores, Madeira, Canary Islands, and Cabo Verde. Although past studies suggest that most plastic items collected on these islands are from offshore regions, their actual sources remain unclear to present date. As such, we focus on the characterization of the potential sources and pathways of plastic particles reaching the Macaronesia archipelagos. This is achieved by combining modeled datasets for ocean currents, winds and waves with a Lagrangian tool used to track virtual particles released around the archipelagos for a 10-year period, making a distinction between surface and submerged particles. Global drifter trajectories are also assessed, selecting those that intercept the archipelagos. Our results demonstrate that the North Atlantic subtropical gyre is the most conspicuous feature in particles and drifter trajectories. The Gulf Stream acts as the main pathway for all archipelagos at a regional scale, though with less significance to Cabo Verde. Surface particles are connected to regional sources in a shorter timescale than mixed particles, mainly because of the wind. Intercepting high-windage particle trajectories are dominant at the center of the North Atlantic subtropical gyre, demonstrating that particles originating from the North Atlantic “garbage patch” are most likely to intercept the archipelagos if considerably exposed to the wind. Regarding the connectivity to sources, all archipelagos are significantly exposed to areas of intensive fishing activity, mainly those located in the Gulf Stream (Azores), in international waters off the Portuguese coast (Madeira and Canary Islands) and along the Northwestern African coast (Cabo Verde). The east coasts of Central and North America are the main sources of land-based particles reaching the Azores, Madeira, and Canary Islands, whereas the Northwestern African coast is the main source for land-based particles reaching Cabo Verde. Our results demonstrate how vulnerable the Macaronesian archipelagos are to marine plastic pollution, highlighting the urgency for international cooperation to mitigate the exposure of oceanic islands to marine plastic pollution.

Seasonal variation in microplastics and zooplankton abundances and characteristics: The ecological vulnerability of an oceanic island system

“…Madeira Island is located on the external range of the North Atlantic Subtropical Gyre, an area of convergence where plastic debris is known to accumulate (Cozar et al, 2014). Through a modeling study, Cardoso and Caldeira (2021) found that Madeira Archipelago is significantly vulnerable to marine litter originating from distant sources. Litter particles, predominantly coming from the west coast of North America, are drifted by southward currents to Madeira (Gulf stream, Azores Current, Portugal, and Canary currents), mainly intercepting the north side of the island.…”

“…A correlation between the monthly average precipitation and the microplastic abundance was not found in the present study, but a significant positive correlation was found between precipitation and zooplankton abundance. In comparison with estuarine or coastal environments, it can be expected that particles accumulation and dispersion in waters surrounding oceanic islands are more heavily subjected to physical oceanographic processes such as currents and winds, respect of surface run-off due to local meteorological events (Gove et al, 2016;Cardoso and Caldeira, 2021;Rosa et al, 2022). However, recent findings highlighted the underestimated impact of surface run-off episodes on suspended particulate matter and Chla concentration in waters surroundings Madeira Island (Rosa et al, 2022).…”

“…Madeira Island is located at the edge of the Atlantic subtropical gyre, affected mainly by the Azores Current (Caldeira et al, 2002). Such subtropical current circulation can mediate the transportation and accumulation of plastic particles (Cardoso and Caldeira, 2021). The study area is also characterised by a relatively steady wind regime, under a predominant northeasterly flow, corresponding to the NE Atlantic trade winds (Caldeira et al, 2002).…”

“…However, local events of island surface run-off, with discharges of freshwater, terrigenous sediments, suspended matter and nutrients, can also significantly contribute to IME (Rosa et al, 2022). Similarly, the transport and distribution of plastic particles have been described in relation to physical processes such as ocean currents and wind (Cardoso and Caldeira, 2021;Brach et al, 2018) or precipitation events (Lima et al, 2015), and their seasonal variations can determine the convergence, accumulation, or dispersion of marine litter.…”

Sources of marine debris for Seychelles and other remote islands in the western Indian Ocean

“…Turrell, 2020b), beaching is often parameterised by explicitly removing particles based on criteria, such as particles entering a land cell due to Stokes drift, wind and/or numerical error (e.g. Zhang et al, 2020;Cardoso and Caldeira, 2021), particle stagnation (e.g. Seo and Park, 2020;Bosi et al, 2021), or as a stochastic process associated with some probability (e.g.…”