250 / 2024-09-12 16:52:24

Missing dissolved arsenic in the deep seawater around various abyssal systems

arsenic biogeochemistry,particle removal processes,abyssal systems

The oceanic cycling of arsenic (As) is closely linked to that of nutrient and trace metal elements such as phosphorus (P) and iron (Fe), primarily due to similar particle-reactive properties of As and P associated with various particulate carriers including Fe oxides. However, the particle scavenging effect is rarely imprinted by seawater profiles of total dissolved inorganic As (DAs), which typically resemble those of nutrients showing increasing concentrations from the surface to stable values at depth. Departing from conventional views, we observed distinct decreases in DAs concentrations in deep waters around independent abyssal systems in the subtropical western North Pacific, which include hydrothermal vents, seamounts, and island sediments. Such DAs removal essentially corresponds to elevated dissolved and particulate Fe concentrations, indicating a major control of particle adsorption on As behaviors in specific regions of the deep ocean. Moreover, the particle scavenging effect varied among these regions mainly ascribed to changing particulate elemental compositions, as well as influenced by diverse environmental factors of pH, temperature, and dissolved oxygen. Our findings highlight an overlooked sink term of DAs removal from seawater by particles of various abyssal origins. The new estimation of output fluxes around either hydrothermal or seamount systems is comparable to an individual input flux from rivers, atmosphere, and hydrothermal vents, and thus has potentials to balance the global oceanic As budget.