Constraining ocean ventilation pathways and time scales with observations and models

The ocean's key role in regulating Earth's climate is in large part due to its thermohaline circulation that transports water and climatically important trace gases such as carbon dioxide from the surface into the ocean interior and back to the surface. This so-called "conveyor belt" circulation allows the ocean to absorb and sequester CO2 and heat on centennial to millennial time scales, thus potentially mitigating the impact of anthropogenic climate change. Quantitatively characterizing this complex circulation is an important problem in oceanography and climate science but remains highly challenging because of the eddy-diffusive nature flow of the flow and the scarcity of observations. In this talk I will present a mathematically rigorous approach to characterizing ocean circulation based on Green's functions that accounts for the multiplicity of transport pathways and transit times characteristic of the ocean's turbulent flow. I will use observations and simulations from global ocean general circulation models to illustrate these ideas and describe their implications for our understanding of the ocean's large scale circulation and CO2 uptake.