Significant contribution of authigenic carbonate to marine carbon burial

Carbon is removed from the Earth's surface through the formation and burial of carbon-bearing rocks and minerals(1,2). The formation of calcium carbonate and its burial in marine sediments accounts for around 80% of the total carbon removed from the Earth's surface. However, the fraction of calcium carbonate that precipitates in the oceans, versus that which precipitates authigenically in marine sediments, is unclear. Here, we compile measurements of the calcium concentration of pore fluids collected at 672 seafloor sites around the globe to calculate the global flux of calcium within marine sediments. We use these data, combined with alkalinity measurements of pore fluids, to quantify authigenic calcium carbonate precipitation. We estimate that the net calcium flux into marine sediments that can be ascribed to authigenic carbonate precipitation amounts to around 1 x 10(12) mol yr(-1). As such, we estimate that authigenic carbonate precipitation accounts for at least 10% of global carbonate accumulation. We show that much of the precipitation occurs along the eastern margins of ocean basins, where organic matter delivery to the sea floor is likely to be high. We suggest that authigenic calcium carbonate precipitation represents a non-negligible component of the global carbon cycle.