A wave energy converter (100) is provided which comprises a heaving buoy point absorber (122) having a surface piercing float (120) operably coupled to an adjustable reference mass (125) defining a volume for accommodating sea water therein. The surface piercing float and the adjustable reference mass are configured to move together in response to passing waves. A chamber (105) provided within the surface piercing float is in fluid communication with the sea for trapping a volume of air above an enclosed column of water. The height of the enclosed column of water varies as the point absorber reacts against its surface via an adjustable air-spring. A power take off (140) is configured for being driven by a stream of vented air in communication with the chamber as the heaving buoy point absorber reacts against a trapped volume of air. A control mechanism is configured for tuning one or more operating characteristics of the heaving buoy point absorber.