Abstract. Mode Waters are thick, vertically homogeneous upper ocean water masses, important for the storage, transport, and ventilation of anomalous heat, CO2, and nutrients. Argo data reveal that the winter of 2011-2012 was a particularly weak season for the formation of Subtropical Mode Water (STMW) in the western North Atlantic. Buoyancy content anomalies and surface buoyancy fluxes are evaluated over this winter and compared with those of previous winters exhibiting more vigorous STMW formation, particularly that of 2006-2007. A combination of factors led to this year’s anomalously weak STMW: The 2011-2012 formation season was preconditioned by enhanced autumn buoyancy content in addition to experiencing weaker than usual late winter buoyancy loss, likely related to the high, positive phase of the North Atlantic Oscillation (NAO) and the northerly separation latitude of the Gulf Stream.