The Potential Role of Bering Strait in the Dynamics of Multi-decadal Variability in the North Atlantic: an idealized model study

Abstract

Multi-decadal variability on time-scales between 20 and 70 years have been observed in the time-series of North Atlantic SST. Many mechanisms have been proposed to explain multidecadal variabilities in Atlantic. Generally, it is the interaction between the MOC and North Atlantic surface buoyancy distribution that sustains this variability, with buoyancy anomalies either due to ocean-only processes or to air-sea interactions. In this context, the role of the Arctic Ocean, especially its freshwater flux into the North Atlantic, has been under-appreciated. Bering Strait, the only oceanic pathway between the Pacific Ocean and the Arctic Ocean, has been found important in Arctic Ocean freshwater budget and in modulating the time-averaged state and long-term response of the MOC to high-latitude buoyancy forcing anomalies, via freshwater transport between the Pacific and Atlantic Oceans. In this paper, we use idealized configurations that include a Pacific-like wide basin and an Atlantic-like narrow basin. The two basins are connected both in the south and north to longitudinally periodic channels, representing the Southern Ocean and the Arctic Ocean respectively. The Pacific-like basin is opened to the north only through a shallow and narrow strait, while the Atlantic-like basin is fully open to the north. With the goal of studying the role of Bering Strait in the multi-decadal variability, we find that the freshwater transport from the Bering Strait forms a tongue-structure along the western boundary of the narrow basin, which enhances the local horizontal density gradient. The western boundary region becomes unstable to large-scale baroclinic anomalies, giving rise to multi-decadal variability.