Alexander Joseph Hammerstrom, Rita Parai, Richard Carlson, Stephen Turner

Accurate estimates of carbon recycling efficiency at subduction zones are crucial for understanding the long-term evolution of the planet’s climate. Estimating subducting carbon recycling efficiency is difficult, however, due to magmatic degassing deep within the crust. Stable strontium (δ88Sr) isotopes have the potential to serve as an additional proxy for carbonate recycling due to carbonate’s high Sr concentrations and unique δ88Sr composition. New data from Nicaraguan lavas and sediments verify that Sr can indeed be used to track subducting carbon. When interpreted in conjunction with other magmatic trace element abundances, these data reveal systematic variations that are best understood as the effects of seamount subduction. Seamounts erupting at the same time carbonate-dominated sedimentation ceased on the Cocos plate could potentially ‘cap’ the carbonate layer and control the degree to which carbonate material is transported to the arc. This model can also be used to quantify the flux of carbonate sediment from the slab to the arc and thus provides an independent method to estimate the magmatic carbon recycling efficiency for the Nicaraguan Arc. Our model shows, absent seamounts, 26% to 52% of carbon from subducted carbonate is returned to the arc, an estimate consistent with recent estimates made from volcanic gases.