1379 / 2024-09-26 03:16:45

Bottom-up control of dissolved Ba isotope distributions in the deep ocean

Ba isotopes,benthic inputs,pore fluid,non-conservative

The distributions of dissolved Ba concentrations ([Ba]) and isotope compositions (d¹³⁸Ba) in the deep waters of the open ocean are thought to be primarily controlled by physical mixing between water masses of different origins. However, a limited number of near-bottom water samples from the North Atlantic show notable deviations from the expected conservative mixing behaviour. This indicates that deep-water d¹³⁸Ba is likely altered by benthic fluxes of Ba from deep-sea sediments. To address uncertainties in the global oceanic Ba budget and the role of benthic fluxes in seawater d¹³⁸Ba distributions, we present new data on [Ba] and d¹³⁸Ba from sedimentary pore fluids and overlying water columns in the Atlantic, Pacific and Southern Oceans. Our results demonstrate significant Ba enrichment in pore fluids relative to bottom seawater, highlighting benthic input as a key source of Ba to the deep ocean. In addition, the δ¹³⁸Ba signatures in core-top pore fluids closely match those in overlying water masses, suggesting that benthic Ba fluxes play a crucial role in regulating deep-water δ¹³⁸Ba signatures. These findings provide direct evidence that sediment pore fluids are a major source of Ba to the global ocean and suggest that the benthic fluxes exert a primary control over the deep ocean δ¹³⁸Ba distributions.