Predicting Rates and Distribution of Carbonate Melting in Oceanic Upper Mantle: Implications for Seismic Structure and Global Carbon Cycling

Coupling a global mantle flow model with a parameterized carbonate solidus, we examine the global distribution and extent of carbonate melting beneath the ocean basins. We predict carbonate melting in spatially heterogeneous patterns throughout the oceans. The rate of CO₂ segregation from the mantle by off-axis carbonate melting (~1.1 × 10¹² mol/year) is comparable to the global ridge flux (~1.2 × 10¹² mol/year). As the generation of carbonate melts should be enhanced in regions of mantle upwelling, we compare upwelling patterns with seismic detections of the G-discontinuity. The upwelling velocities in areas where the G-discontinuity is detected are not statistically different from areas with no detections—implying that the generation and pooling of carbonate melts are not dominant mechanisms in forming the G-discontinuity. However, detections of a deeper seismic discontinuity are correlated with enhanced upwelling velocities, suggesting locally higher melt fractions at the transition between carbonate-only and carbonate-enhanced silicate melting.