North Atlantic Ocean Circulation and Related Exchange of Heat and Salt Between Water Masses

Abstract

The circulation in the Atlantic Ocean is a key component of the Earth's climate system (Bindoff et al., 2019;Bower et al., 2019;Weijer et al., 2020). The Atlantic Meridional Overturning Circulation (AMOC) transports surface water to the northernmost parts of the Atlantic Ocean. On its way, the water looses heat and freshens, which results in a net increase in density. These changes are due to a combination of air-sea interactions, such as heat fluxes through the surface or evaporation and precipitation, and through internal mixing (Berglund et al., 2017;Bower et al., 2019;Lozier, 2012). When the water reaches the northern parts of the Atlantic Ocean it is sufficiently dense to sink and return southwards. This watermass transformation from light to dense waters is gradual on its northward path and to a large extent subsurface within the North Atlantic Current and in the Subpolar Gyre in a depth range of 800-1,500 m (Chafik & Rossby, 2019;Evans et al., 2022;Zhang & Thomas, 2021).In the present study, we will investigate to what extent this subsurface transformation is due to mixing with other water masses and thus not only due to the heat and freshwater fluxes through the sea surface. The northward heat transport, associated with the AMOC, is considered to be one of the reasons for the relatively mild climate of