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The short residence times of Th and Pa in seawater make them very responsive to changes in the ocean environment. We use a new multi-ion-counting technique to make Th and Pa isotope measurements in seawaters from a near-shore environment in which oceanic chemical tracers are not overwhelmed by terrestrial inputs (the Bahamas). An unusual feature of the Bahamas setting is the shallow depth of water residing on the bank tops. These waters have significantly lower ²³²Th/²³⁰Th (∼10,000) than those immediately adjacent to the banks (24,000–31,000) and a (²³¹Pa/²³⁰Th) near the production ratio (∼0.1). The change in ²³²Th/²³⁰Th and (²³¹Pa/²³⁰Th) on the bank tops is explained by almost quantitative removal of Th and Pa by scavenging, and their replacement with a mixture of ²³⁰Th and ²³¹Pa alpha-recoiled from the underlying carbonates, together with Th from dust dissolution. Analysis of a …