A Tale of Two Timescales: Weddell Polynya Pathways in the Global Abyssal Oceans

We examine the dynamical pathways by which signals arising from Weddell Sea polynyas reach the global deep and abyssal oceans in the GFDL CM2G coupled climate model. Although the model is capable of creating open-ocean convection internally, its convective events differ widely in strength and spatiotemporal extent. As a result, their consequences can be difficult to cleanly separate from unrelated internal model variability. The differences between individual polynyas ultimately lead to large uncertainties when quantifying the magnitude of polynya-induced trends in abyssal ocean properties such as temperature and salinity. In this study, we attempt to further elucidate the oceanic impacts of Weddell Sea polynyas by periodically forcing them via an increase in the diapycnal diffusivity in a region of the Weddell Sea. Using a combination of passive tracers and isopycnal heave analysis we find that polynya signal propagation is primarily determined by two processes acting on different timescales and spreading at different rates: 1) planetary waves that act on decadal-to-multi-decadal timescales, and 2) advection and diffusion that act on multi-decadal-to-centennial timescales. In regions near the Weddell Sea, both processes are responsible for perturbing local deep and abyssal ocean properties. In remote regions such as the North Atlantic and Equatorial Pacific, planetary waves are largely responsible.