Systems and methods for lifting drilling fluid from a well bore in a subsea formation are disclosed. Some system embodiments include a drill string suspended within a drilling riser to form the well bore, and a drilling fluid source for supplying drilling fluid through the drill string during drilling. A diverter is coupled between the drilling riser and a return line, while a power riser coupled to the return line at an interface. A lift fluid source supplies lift fluid through the power riser into the return line. The lift fluid is intermittently injected from the power riser through the interface into the return line to form one or more slugs of lift fluid positioned between slugs of drilling fluid, such that the combined density of lift fluid and drilling fluid in the return line is less than the density of the drilling fluid alone.