A dynamical systems analysis of deep ocean convection with applications to the subpolar North Atlantic

Ocean convection is an essential component of the climate system. In the Labrador Sea of the North Atlantic, convection can be particularly deep and intense, forming the downward branch of the Atlantic Meridional Overturning Circulation (AMOC). Increased freshwater input to the Labrador Sea resulting from melting Greenland ice caps puts convection at risk of shutting down. This could weaken the AMOC and would have wide impacts on global climate. Here, we represent ocean convection in a two-box model with seasonal forcing. The model may exhibit various convective regimes, including where convection is permanently shut down. Despite its simplicity, the model reproduces the observed variability well. We explore the possible climate regimes of the two-box model by fitting its parameters to a variety of observation-based datasets, including the Arctic Subpolar gyre sTate Estimate (ASTE), gridded Argo data and CMEMS reanalysis. We construct bifurcation diagrams showing the proximity of the system to a deep convective shutdown. Results suggest that in the Labrador Sea this shutdown is not as close as suggested in previous literature. Our approach allows a deeper understanding of the dynamics of a deep convective shutdown and provides improved estimates of deep convective stability.