Carbon Fluxes and Primary Magma CO 2 Contents Along the Global Mid‐Ocean Ridge System

• Published in: Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2019-03, Vol.20 (3), p.1387-1424
• Main Authors: Le Voyer, Marion, Hauri, Erik H., Cottrell, Elizabeth, Kelley, Katherine A., Salters, Vincent J. M., Langmuir, Charles H., Hilton, David R., Barry, Peter H., Füri, Evelyn
• Format: Article
• Language: English
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2018GC007630

The concentration of carbon in primary mid‐ocean ridge basalts (MORBs), and the associated fluxes of CO 2 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 CO 2 . We thus use the limited range in CO 2 /Ba (81.3 ± 23) and CO 2 /Rb (991 ± 129), derived from undegassed MORB and MORB melt inclusions, to estimate primary CO 2 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 CO 2 abundances 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 × 10 5 to 3.0 × 10 8 m 3 /year) and an integrated global MORB magma flux of 16.5 ± 1.6 km 3 /year. When combined with CO 2 /Ba and CO 2 /Rb‐derived primary magma CO 2 abundances, the calculated segment‐scale CO 2 fluxes vary by more than 3 orders of magnitude (3.3 × 10 7 to 4.0 × 10 10 mol/year) and sum to an integrated global MORB CO 2 flux of  × 10 12 mol/year. Variations in ridge CO 2 fluxes have a muted effect on global climate; however, because the vast majority of CO 2 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. Estimated CO 2 contents of primary mid‐ocean ridge basalts (MORB), calculated on a segment‐by‐segment basis, vary from 104 ppm to 1.9 wt%. CO 2 ‐enriched MORB are present in all ocean basins, in particular, in the Atlantic Ocean basin, which is younger and more likely to contain admixed material from recent subduction compared to the much older Pacific Ocean basin. CO 2 fluxes at individual ridge segments vary by 3 orders of magnitude due primarily to large variability in primary CO 2 content. This study provides the most detailed and accurate estimate to date of the integrated total flux of CO 2 from mid‐ocean ridges of  × 10 12 mol/year. New analyses (753) and compiled data (2,446) for volatiles CO 2 , H 2 O, F, S, and Cl are reported in a global suite of mid‐ocean ridge basalts Estimated primary MORB CO 2 contents vary from 104 ppm to 1.9 wt% and are the result of variations in mantle composition High CO 2 fluxes at rid