Anthropogenic CO2 uptake, transport, storage, and dynamical controls in the ocean imposed by the meridional overturning circulation: A modeling study

Using an ocean carbon cycle model embedded in an ocean general circulation model, we examine how the budget of anthropogenic CO2 (C-ant) is controlled by ocean dynamics. To complement recent studies showing only vertically integrated budgets, we provide a step-by-step description by making use of three different coarse grainings of the full vertical resolution of the ocean model in our budget analysis. For the 11 subdomains of the global ocean, these coarse grainings are (1) a one-layer (vertically integrated) budget, (2) a three-layer budget, and (3) an 11-layer budget. We largely focus on the Pacific circulation. We identify and quantify substantial carbon transport associated with the subtropical cells (STCs), which are dominant contributors to the meridional overturning circulation in the upper ocean in the tropics and subtropics, as playing a fundamental role in governing the ocean interior distribution of C-ant. The upper branch of the STCs transports C-ant-rich water from the tropics to the subtropics, contributing to the precondition for the high C-ant inventory in mode waters. The lower branch of the STCs carries about two thirds of the transported C-ant back to the tropics, while it largely excludes Subtropical Mode Waters. This work implies that the reemergence of C-ant through recirculation within the STCs may lead to a reduced capacity for further C-ant uptake via gas exchange into the surface ocean, potentially contributing to a positive carbon-climate feedback.