Abstract

Dense gravity currents forced by surface buoyancy loss over polar continental shelves are important contributors to subsurface and abyssal ventilation throughout the World Ocean, yet remain challenging to observe and represent accurately in models. The vast, and rapidly evolving Arctic shelves are particularly crucial in setting water mass structure of the entire basin and influencing its response to changing climatic conditions. Observations indicate that some of the strongest water mass transformation processes in the Arctic occur in the Barents and Kara Sea shelves. The combination of cooling of warm Atlantic inflow as well as localized polynya development around Svalbard, Franz Josef Land, and Novaya Zemlya leads to development of waters with higher densities than even the deepest layers of the Arctic. Depending on the amount of mixing and strength of the buoyancy forcing, these dense overflows may also ventilate the Arctic halocline layer.

In the first part of the talk, I will present idealized high-resolution simulations aimed at studying the dynamics of rotating dense overflows. I will discuss the role of mesoscale baroclinic eddies and submesoscale symmetric instability in setting the pathways and properties of the dense waters. In the second part, we will examine how modern state-of-the-art general circulation models presently capture shelf overflow dynamics in the Arctic. We consider: (1) whether dense shelf overflows and the vertical structure of the Arctic are well-represented by the GFDL -OM4 1/4-degree model as well as an analogous 1/8-degree version; and (2) pathways by which overflows and water mass transformation over the Eurasian shelves contribute to setting the vertical structure of the interior Arctic. We also explore the changes in ventilation pathways that the Arctic will experience as a result of warming. In particular – we see evidence for dense water formation changing from being influenced by polynyas and brine rejection as sea ice forms to being predominantly set by cooling of the inflowing, highly saline Atlantic waters.