Modelling the impact of AMOC variability on carbon uptake and transport in the North Atlantic Ocean using an inverse water mass model

The North Atlantic is an important region when considering the global ocean’s absorption of anthropogenic carbon emissions. The North Atlantic carbon sink has variability which is linked to the Atlantic Meridional Overturning Circulation (AMOC). Currently, continuous observational data of the AMOC is limited to the RAPID and OSNAP mooring arrays at specific latitudes which have been in situ since 2004 and 2014, respectively. Ocean models can be used to produce data with greater spatial and temporal coverage, but these are often not constrained by observations. This leads to a great uncertainty in how AMOC variability in a changing climate may impact carbon uptake in the North Atlantic. The EXPLANATIONS project aims to tackle this problem by increasing our understanding of the North Atlantic carbon sink and the ocean interior carbon transports. We utilize an inverse water mass model, the Optimal Transformation Method (OTM) to estimate the transports and mixing of tracers between and within ocean basins. OTM simultaneously solves budgets of heat, freshwater, and carbon in a manner consistent with ocean reanalysis and carbon product data. We compare the observed data at RAPID and OSNAP with the OTM solution by defining a North Atlantic domain between the two mooring arrays. We use the data collected from these arrays to further constrain the inverse model, thus giving a better representation of the AMOC and its impact on carbon. Output from OTM informs upon the transports and mixing of volume, heat, freshwater, and carbon between and within the ocean basins. It allows for the construction of carbon budgets within the North Atlantic, improving our understanding of how these may change with variability in the AMOC.