The global Meridional Overturning Circulation (MOC) regulates the oceanic uptake, transport and upwelling of heat and natural and anthropogenic tracers, therefore contributing to the regulation, variability and anthropogenic change of our climate. Here, I will focus on the role of cross-density mixing to (i) contributing to the closure of the lower cell of the global MOC, and (ii) controlling the distribution of tracers within the Atlantic MOC (AMOC). First, I will discuss the sensitivity of cross-density mixing - and so of the strength of the lower cell of the circulation - to variations in internal wave energy distribution and mixing efficiency. I will show that the combined variations of these two parameters significantly modifies the patterns of upwelling and downwelling of dense waters, with implications for the inter-basin exchange of water masses and tracers. Second, I will discuss the role of cross-density mixing in the Atlantic Ocean, and especially within the density classes of the upper cell of the AMOC, i.e. of the dense waters of North Atlantic origin flowing southward. By analyzing different estimates of cross-density mixing (both observational and theoretical), I will show that there is a significant amount of cross-density mixing within the southward flowing waters of the upper AMOC, and that this leads to the potential exchange tracers between different water masses prior to their entry in the Southern Ocean, thus potentially leading to different tracers pathways and ventilation timescales.
Wednesday 30 January 2019 - 11:00 to 12:00
NOC Southampton - Node Room (074/02) (Waterfront Campus).
Laura Cimoli (University of Oxford)