Seasonal changes in bay water column properties and their influence on the distribution of dissolved and particulate substances along the south coast of Curaçao (Caribbean Sea)

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As endpoints of watersheds, bays concentrate erosion- and human-derived substances such as dissolved inorganic nutrients and pollutants. We investigated the water movement and biogeochemistry of two bays in Curaçao: Piscadera Bay and Spaanse Water, during the dry (May 2022 and 2023) and wet seasons (November 2021 and 2023). Bay-ocean exchange was limited during the dry season, enhancing nutrient concentrations in the bays. The wet season showed increased mixing between bay and offshore water. Extreme rainfall from the 2023 El Niño event led to heavy runoff and wastewater influx, particularly in Piscadera Bay, where enriched δ 15 N and total xenobiotic concentrations were over 1.5 times higher than in the dry season. Elevated δ 15 N and δ 13 C values reflected greater terrestrial influence in Piscadera Bay. These findings show how extreme weather, likely under future climate scenarios, can enhance nutrient and pollutant export from bays to reefs. • Bay-ocean exchange is higher during wet seasons compared to dry seasons in Curaçao. • Elevated xenobiotic levels and isotopic data in bay water reflect increased runoff and land derived substances during wet seasons. • Bays act as nutrient and substance reservoirs in dry seasons, releasing them during wet periods. • El Niño in 2023 increased nutrient export from bays to coastal reefs.