The seasonal mixed-layer pump (MLP) transfers biologically produced carbon to the ocean interior via seasonal changes in mixed-layer depth, providing an important physically mediated pathway for carbon export. However, its global contribution remains poorly constrained. Here we use 664 float-years of observations from 397 biogeochemical Argo floats to quantify MLP carbon export across the global ocean. Local MLP export rates range from −1.4 to 9.7 g C m^-2 yr^-1, equivalent to up to 60% of gravitational particle export, and are primarily modulated by upper-ocean stratification and nutrient availability. Extrapolating these float-based estimates globally with a machine-learning model yields a global annual MLP export of 0.29 ± 0.01 Pg C yr^-1, with the North Atlantic and Southern Ocean emerging as global hotspots. These results identify the seasonal MLP as an important regional pathway and underscore how changes in upper-ocean vertical structure can reshape regional carbon export budgets.
 

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