Eddy effects on South Atlantic Ventilation Pathways using Lagrangian trajectories

The Southern Ocean takes up a significant amount of anthropogenic CO₂ emissions by subduction, as dense water masses get displaced northward and form the Antarctic Intermediate Water (AAIW).  Subducting oceanic water masses encapsulate dissolved atmospheric gases and retard anthropogenic climate change by taking up about a quarter of industrial CO₂ emissions, nearly half of which in the Southern Ocean. However, the processes that control the water mass formation and their ventilation pathways, relevant to climate change remain actively researched. Southern Ocean dynamics are strongly influenced by mesoscale eddies which are likely to intensify in a warmer global climate, raising the question on the role and importance of eddies in shaping the ventilation pathways and in oceanic tracer and heat uptake. Previous results using Lagrangian backtracking and tracer simulations in the South Atlantic Ocean indicate heterogeneous source regions and pathways for AAIW, suggesting the potential role of eddies in addition to wind stress-induced Ekman Transport. Here we investigate the impact of mesoscale eddies on the subduction timescales and ventilation pathways of the AAIW in the South Atlantic Ocean.  
   
We use an eddy-resolving 1/10 degree ocean model (Parallel Ocean Program) with a Lagrangian particle tracking algorithm (Parcels) following discrete particles from the interior of the South Atlantic AAIW backward in time until they reach the mixed layer after tracking them for 100 years. In total 10⁵ particles were released in the South Atlantic Ocean between 15° and 40°S in depths that meet the density criteria of 26.8 to 27.4 kg/m³  for the AAIW. The experiment was performed on a repeated year velocity field with daily mean data from 1990. For comparability, we performed the same experiment on a decadal mean state, eliminating mesoscale eddy activity. The Transit Time Distributions (TTD) inferred from the backtracking of Lagrangian trajectories aid in quantifying eddy effects on the advection time scales, source regions, and pathways of the AAIW. We expect eddy effects to alter the position and time scales of the subduction process and affect the importance of specific routes, such as the cold and warm water routes.