Enhanced North Pacific biological pump contributed to atmospheric carbon dioxide plateau during the Bølling-Allerød period

Carbon dioxide release from the Southern Ocean is generally recognized as a primary factor driving atmospheric carbon dioxide rise during the deglaciation; however, the Bølling-Allerød period saw an atmospheric carbon dioxide plateau, despite diminished biological pump and enhanced ventilation in the Southern Ocean favoring carbon dioxide outgassing. Here we, by compiling productivity records based on multiple geochemical and paleontological proxies, suggest that this plateau was achieved by basin-wide elevated biological pump in the oligotrophic North Pacific. This basin-scale carbon sink is a result of oligotrophy and stratification, allowing for prolonged and complete consumption of deep-sourced nutrients and carbon dioxide in the deepened euphotic zone when North Pacific Intermediate Water was sluggish. This carbon sink is amplified by synchronously enhanced stratification-induced nitrogen fixation. Extending the Bølling-Allerød warming-biological pump analogy to current and future warming scenarios, however, is constrained by human-forced biogeochemical-physical processes, yielding large uncertainties in biological pump responses and feedbacks. Basin-wide elevated biological pump uptake of carbon dioxide in the oligotrophic North Pacific decelerated atmospheric carbon dioxide rise in the Bølling-Allerød interstadial, according to analysis of deep water cores from the South China Sea.