| Summary: | The concentration of carbon in primary mid-ocean ridge basalts (MORBs), and the associated fluxes of CO2 outgassed 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, thus we 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 CO2 concentrations 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 CO2 abundances that varies from 104 ppm to 1.90 wt%. Segment-scale data reveal a range in MORB magma flux varying by a factor of 440 (from 6.8x105 to 3.0x108 m3/yr) and an integrated global MORB magma flux of 16.5±1.6 km3/yr. When combined with CO2/Ba and CO2/Rb-derived primary magma CO2 abundances, the calculated segment-scale CO2 fluxes vary by more than three orders of magnitude (3.3x107 to 4.0x1010 mol/yr) and sum to an integrated global MORB CO2 flux of x1012 mol/yr. Variations in ridge CO2 fluxes have a muted effect on global climate, however, because the vast majority of CO2 degassed 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.
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