Evidence for a Global Slowdown in Seafloor Spreading Since 15 Ma

The rate of ocean-crust production exerts control over sea level, mantle heat loss, and climate. Different strategies to account for incomplete seafloor preservation have led to differing conclusions about how much production rates have changed since the Cretaceous, if at all. We construct a new global synthesis of crust production along 18 mid-ocean ridges for the past 19 Myr at high temporal resolution. We find that the global production rate during 6-5 Ma was only 69%-75% of the 16-15 Ma interval. The reduction in crust production is mostly due to slower seafloor spreading along almost all ridge systems. While the total ridge length has varied little since 19 Ma, some fast-spreading ridges have grown shorter and slow-spreading ridges grown longer, amplifying the spreading-rate changes. Our production curves represent a new data set for investigating the forces driving plate motions and the role of tectonic degassing on climate.