Map of the Lesser Antilles volcanic arc showing the subduction zone trench and the location of two Deep Sea Drilling Cores
Map of the Lesser Antilles volcanic arc showing the subduction zone trench (white dashed line) and the location of two Deep Sea Drilling Cores, DSDP Site 543 and site 144. The drill cores were used to determine the carbonate and organic carbon contents and carbon isotope values of sediments and underlying pillow basalts down to 455 meters depth below the sea floor. Volcanic carbon output along the arc was calculated from previously published emission fluxes and used to generate a three-endmember mixing model between depleted mantle, slab carbonate, and slab organic carbon. The results for Central-Northern Lesser Antilles indicate nearly complete slab carbon recycling at sub-arc depths, with little or no loss to the forearc region, or deeper carbon subduction. The observations highlight strong variability in carbon recycling efficiency along different subduction zones at a global scale. Credit: Li et al. [2020], Figure 1
Source: Geophysical Research Letters

The efficiency of carbon recycling at volcanic arcs assesses the degree to which subducted carbon in sediment and altered oceanic crust escapes into the forearc region, is degassed in arc volcanism, or gets subducted deeper into the Earth’s mantle. By examining the carbon recycling efficiency of arcs at individual subduction zones, a more accurate model of global carbon recycling will become possible.

Previous estimates for the release of subducted carbon along various volcanic arc systems range considerably, from very little (under 25%) to amounts that are greater than the expected sedimentary carbon being subducted. A critical gap in our understanding of carbon recycling efficiency at arcs comes from poor constraints on the amount of carbon in altered oceanic crust below the sedimentary carbon.

Li et al. [2020] used two drill cores off the Lesser Antilles trench to constrain the average carbon isotope values and total carbon concentrations in the subducted slab, finding roughly 1.28 x 1010 mol C/yr with an average δ13C = -2.7 per mil. Using instrument data to constrain a model of volcanic arc degassing, it was found that the release of carbon along the Central to Northern Lesser-Antilles arc is essentially the same, implying 100% carbon recycling efficiency.

The extremely high loss of carbon at sub-arc depths implies very little carbon is being lost to the forearc or being subducted deeper into the mantle. This study highlights the importance of evaluating individual subduction zones to improve global models of the deep carbon cycle.

Citation: Li, K., Li, L., Aubaud, C., & Muehlenbachs, K. [2020]. Efficient carbon recycling at the Central‐Northern Lesser Antilles arc: Implications to deep carbon recycling in global subduction zones. Geophysical Research Letters, 47, e2020GL086950.

—Steven D. Jacobsen, Editor, Geophysical Research Letters

Text © 2020. The authors. CC BY-NC-ND 3.0
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