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Abstract Oxic pelagic clays are an important component of seafloor sediment that may hold valuable information about past ocean chemistry due to their affinity for and accumulation of biogeochemically important metals. We present a new approach to calculating site‐specific sedimentation rates (SRs) by comparing authigenic sediment thorium isotope compositions (²³⁰Th/²³²Th) to seawater dissolved²³⁰Th/²³²Th in a suite of deep (>3,000 m) pelagic core sites. We extracted the authigenic sediment fraction using an HHAc leach protocol, which major element chemistry (Al, Mn, Fe, Ti) suggested was less affected by lithogenic contamination than the HCl leach. Four different methods were tested for extracting the appropriate initial²³⁰Th/²³²Th from seawater: using either the nearest water column station (methods 1 and 2) or a regionally averaged profile (methods 3 and 4) and using either the bottommost profile measurement (methods 1 and 3) or linear regression of the profile and extrapolation to the seafloor (methods 2 and 4). Method 3 outperformed the other methods in reconstructing previously published SRs from pelagic clays in the North Pacific. The new thorium‐based SRs were then combined with estimates from the total sediment thickness on ocean crust and non‐lithogenic cobalt accumulation to determine the best estimates for SRs of oxic pelagic clays. The Pacific has the lowest SR (median 0.28 cm/kyr), while the Atlantic is higher (median 0.46 cm/kyr) and the Indian Ocean is highest (median 0.75 cm/kyr). These new estimates are consistent with the expected spatial patterns of sedimentation, but they revise the absolute SR values downward from available gridded SR maps. 

Abstract Nitrogen (N) dominates Earth's atmosphere (78% N₂) but occurs in trace abundances in silicate minerals, making it a sensitive tracer of recycled surface materials into the mantle. The mechanisms controlling N transfer between terrestrial reservoirs remain uncertain because low N abundances in mineral‐hosted fluid inclusions (FIs) are difficult to measure. Using new techniques, we analyzed N and He isotope compositions and abundances in olivine‐ and pyroxene‐hosted FIs from arc volcanoes in Southern Chile, Cascadia, Central America, and the Southern Marianas. These measurements enable an estimate of the global flux of N outgassing from arcs (4.0 × 10¹⁰ mol/yr). This suggests that Earth is currently in a state of net N ingassing, with roughly half of subducted N returned to the mantle. Additionally, the N outgassing flux of individual arcs correlates with the thickness of subducting pelagic sediment, suggesting that N cycling in the modern solid Earth is largely controlled by sediment subduction.