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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. 

Abstract The concentration of carbon in primary mid‐ocean ridge basalts (MORBs), and the associated fluxes of CO₂outgassed at ocean ridges, is examined through new data obtained by secondary ion mass spectrometry (SIMS) on 753 globally distributed MORB glasses. MORB glasses are typically 80–90% degassed of CO₂. We thus use the limited range in CO₂/Ba (81.3 ± 23) and CO₂/Rb (991 ± 129), derived from undegassed MORB and MORB melt inclusions, to estimate primary CO₂concentrations for ridges that have Ba and/or Rb data. When combined with quality‐controlled volatile‐element data from the literature (n = 2,446), these data constrain a range of primary CO₂abundances that vary from 104 ppm to 1.90 wt%. Segment‐scale data reveal a range in MORB magma flux varying by a factor of 440 (from 6.8 × 10⁵to 3.0 × 10⁸m³/year) and an integrated global MORB magma flux of 16.5 ± 1.6 km³/year. When combined with CO₂/Ba and CO₂/Rb‐derived primary magma CO₂abundances, the calculated segment‐scale CO₂fluxes vary by more than 3 orders of magnitude (3.3 × 10⁷to 4.0 × 10¹⁰mol/year) and sum to an integrated global MORB CO₂flux of × 10¹²mol/year. Variations in ridge CO₂fluxes have a muted effect on global climate; however, because the vast majority of CO₂degassed at ridges is dissolved into seawater and enters the marine bicarbonate cycle. MORB degassing would thus only contribute to long‐term variations in climate via degassing directly into the atmosphere in shallow‐water areas or where the ridge system is exposed above sea level.