Mapping modern CO2 fluxes and mantle carbon content all along the mid-ocean ridge system

Research areas:
Year:
2014
Authors:
Journal:
EARTH AND PLANETARY SCIENCE LETTERS
Volume:
387
Pages:
229-239
Month:
FEB 1
ISSN:
0012-821X
Abstract:
Quality criteria have been used to select similar to 400 vesicularity measurements on zero-age mid-ocean ridge glasses from similar to 600 data available in the literature published over the past similar to 30 years. At face value, observations show that for a given depth of sampling, enriched basalts from slow spreading ridge segments are more vesicular than those from depleted and intermediate or fast spreading ridges. A shallower depth of eruption enhances these effects because lower hydrostatic pressure favours bubble expansion. In order to get an insight into these complex and intermingled processes, we used empirical and semi-quantitative approaches based on a limited number of inputs (segment depth D, spreading rate tau and K2O/TiO2 ratios). Both models give equivalent results and predict vesicularities within +/- 50%. From these calculations, we compute the equivalent CO2 concentration at the depth of eruption all along the oceanic ridge system. The total calculated CO2 fluxes are low ranging from 6.5 +/- 1.8 to 8.7 +/- 2.8 x 10(11) mol/yr and the CO2 mantle content displays large variabilities from 66(-19)(+27) to 78(-40)(+82) ppm. In order to test these results, the mantle He-3 fluxes have been evaluated using the calculated CO2 fluxes and a CO2/He-3 ratio of 2.2 x 10(9). These fluxes range from 295 +/- 82 to 395 +/- 127 mol/yr and are close to the values reported by Jean-Baptiste (1992) (267-534 mol/yr) and the most recent estimate (Bianchi at al., 2010, similar to 527 +/- 102 mol/yr) using box-model of the three main ocean basins constrained by measurements of He-3 and radiocarbon data. As these independent methods give similar helium fluxes at regional and global scales, it provides strong support to a low and heterogeneous mantle carbon concentration and distribution. Finally, the calculated volcanic CO2 emissions at oceanic ridges correspond to similar to 30 seconds of anthropogenic emissions, at current rates. (C) 2013 Elsevier B.V. All rights reserved.