Carbon Fluxes and Primary Magma CO2Contents Along the Global Mid‐Ocean Ridge System

Abstract

AbstractThe 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.