The Role of Seawater Interaction with the Ocean Floor in the Carbon Cycle

Seawater circulation through oceanic crust acts as an essential sink for CO2 and affects the alkalinity budget of the ocean. Seafloor weathering and ridge flank hydrothermal activity contribute to modern carbon sequestration by taking up carbon at a rate < 0.5 Tmol y−1. In addition, these processes release < 1 Tmol y−1 alkalinity to the ocean. During warmer eras in Earth history, the carbon uptake rates were considerably higher. Estimates range between 2.1 and 3.4 Tmol y−1 during the Cretaceous and Jurassic. The more intense carbonation of the seafloor in the Mesozoic is due to higher temperatures and less pelagic sedimentation in the deep ocean. Accelerated rates of reaction between seawater and basalt and prolonged durations of exposure of igneous crust to seawater led to more intense basalt alteration and carbonate formation within the crust. The interactions between oceanic crust and seawater hence profoundly influence global carbon cycling on long time scales.