Exploration of ocean mechanical geoengineering alternatives: effect of diapycnal mixing enhancement on the ocean uptake of atmospheric CO2

Abstract

Many ocean-based geoengineering techniques have been suggested to improve the efficiency of the “biological pump”. Alternatively, in this study we investigate how enhancing diapycnal mixing at specific locations would affect all the forcings that influence the ocean carbon uptake, on decadal time scales. Firstly, we use the Oceanic General Circulation Model (OGCM) of the CSIRO Mk3L Climate System Model, in order to observe the response of the ocean to variations in the parameterization of the vertical diffusivity Kv. This version of the CSIRO Mk3L model is combined with the COAL (Carbon of the Ocean, Atmosphere and Land) component to represent the carbon cycle, nutrient cycling and organic matter cycling in the ocean. In our experiments, the model can also estimate the power added to the system in order to obtain a highly mixed model column. Subsequently, we combine the OGCM with the NOMAD (Nonlinear Optimization by Mesh Adaptive Direct Search) software, with the aim of identifying the locations where a higher Kv would lead to a decline in the partial pressure of CO2 at the ocean surface on short time scales. Lastly, we test our hypothesis using a Community Earth System Model (CESM) that includes the simulation of the global carbon cycle, in order to analyse the combined response from the oceanic, atmospheric and terrestrial components.