The understanding of the deep circulation is continuously evolving thanks to long-term monitoring maintained by fixed moorings, a vast network of Lagrangian floats, as well as high-resolution ocean models, which together allow studies targeted on deep ocean processes, such as deep convection, water mass transformations and mixing.
It is well known that the ocean hold much more heat than any other component of the climate system. Variations and long-term changes in how the ocean redistributes heat towards the upper ocean can therefore have a huge impact on the surface climate. There are no significant deep heat sources in the world oceans and thus the heat budget in the deep ocean is dominated by the balance of vertical advection and vertical diffusion, that is w ∂T/∂z = ∂/∂z(κV∂T/∂z), as suggested by Munk (1966). Deep convection and diapycnal mixing contribute to the transfer and redistribution of water masses and heat throughout the deep oceans. Deep convection is largely controlled by the surface temperature and salinity, and thus future changes in surface conditions have a large impact on the heat budget of the future deep ocean. Diapycnal mixing, in particular, increases the potential energy within a stratified fluid by raising the water mass center on a larger time and spatial scale. This mixing is triggered by external process, e.g. internal waves generated by tides, and is concentrated above seamounts, mid-ocean ridges, and along strong currents.
To understand the deep thermohaline dynamics it is essential to compute the heat content of the deep ocean, how it is redistributed by various processes, and how such processes may change in the future. In particular, understanding the redistribution of heat toward the upper ocean is essential for reducing the climate projection uncertainty on decadal and multidecadal time scale.
This session following a multidisciplinary approach, aims at bringing together oceanographers working on physical and/or biogeochemical processes, using observations as well as state-of-the-art ocean/climate models, with the ambition to fill a knowledge gap on deep processes as well as enhancing predictability of the global oceanic thermohaline circulation and thus climate variability.