Mechanism behind the NAO effect on temperature and salinity of the northern North Atlantic intermediate and deep waters inferred from hydrographic observations

The North Atlantic Oscillation (NAO) is shown to be responsible for up to two thirds of the observed thermohaline changes at the intermediate and deep levels in the northern North Atlantic since the 1950s. Persistent NAO decline leads to warming and salinification in the intermediate–deep water column, and vice versa. Salinity of the intermediate and deep water masses in their formation regions follows the NAO with a time lag of one to several years that corresponds to the fast response of convection activity and the subpolar gyre circulation to the NAO-related changes in the surface forcing inferred from model experiments and observed in nature.