Convection injects labile particulate organic carbon to the deep ocean

Vertical export of particulate organic carbon (POC) is central to the oceanic carbon cycle, yet the role of physical injection processes and their interannual variability remain poorly constrained. Autonomous profilers drifting in the Labrador and Irminger Seas detect recurrent winter-spring chlorophyll-a fluorescence peaks at 1000 m, indicating deep convection of surface POC rich in labile phytoplanktonic material. According to model simulations, convection-driven POC supply to the 500-2000 m depth layer doubles between years of weak vs. strong convection, adding more than 40% to gravitational inputs. These episodic injections likely reshape deep-ocean carbon budgets by enhancing metabolism and driving lateral exports, thereby revealing a critical link between upper ocean dynamics and deep-ocean water masses and ecosystems.