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Abstract An important role in the cycling of marine trace elements is scavenging, their adsorption and removal from the water column by sinking particles. Boundary scavenging occurs when areas of strong particle flux drive preferential removal of the trace metals at locations of enhanced scavenging. Due to its uniform production and quick burial via scavenging,²³⁰Th is used to assess sedimentary mass fluxes; however, these calculations are potentially biased near regions where net lateral transport of dissolved²³⁰Th violates the assumption that the flux of particulate²³⁰Th to the seabed equals its rate of production in the water column. Here, we present a water column transect of dissolved²³⁰Th along 152° W between Alaska and Tahiti (GEOTRACES GP15), where we examine²³⁰Th profiles across multiple biogeochemical provinces and, novelly, the lateral transport of²³⁰Th to distal East Pacific Rise hydrothermal plumes. We observed a strong relationship between the slope of dissolved²³⁰Th concentration‐depth profiles and suspended particle matter inventory in the upper‐mid water column, reinforcing the view that biogenic particle mass flux sets the background²³⁰Th distribution in open ocean settings. We find that, instead of the region of enhanced particle flux around the equator, hydrothermal plumes act as a regional boundary sink of²³⁰Th. At 152° W, we found that the flux‐to‐production ratio, and thereby error in²³⁰Th‐normalized sediment flux, is between 0.80 and 1.50 for hydrothermal water, but the error is likely larger approaching the East Pacific Rise.