The autonomous Lagrangian circulation explorer (ALACE) is a subsurface float that cycles vertically from a depth where it is neutrally buoyant to the surface where it is located by, and relays data to, System Argos satellites. ALACEs are intended to permit exploration of large-scale low-frequency currents and to provide repeated vertical profiles of mean variables. ALACEs periodically change their buoyancy by pumping hydraulic fluid from an internal reservoir to an external bladder, thereby increasing float volume and buoyancy. Because positioning and data relay are accomplished by satellite, ALACEs are autonomous of acoustic tracking networks and are suitable for global deployment in arrays of any size. While providing only a sequence of displacements between surfacing intervals, ALACEs are efficient in gathering the widely spaced long-term observations needed to map large-scale average flow. The primary technical challenges met in the ALACE design are maximizing energy efficiency to achieve a l... Abstract The autonomous Lagrangian circulation explorer (ALACE) is a subsurface float that cycles vertically from a depth where it is neutrally buoyant to the surface where it is located by, and relays data to, System Argos satellites. ALACEs are intended to permit exploration of large-scale low-frequency currents and to provide repeated vertical profiles of mean variables. ALACEs periodically change their buoyancy by pumping hydraulic fluid from an internal reservoir to an external bladder, thereby increasing float volume and buoyancy. Because positioning and data relay are accomplished by satellite, ALACEs are autonomous of acoustic tracking networks and are suitable for global deployment in arrays of any size. While providing only a sequence of displacements between surfacing intervals, ALACEs are efficient in gathering the widely spaced long-term observations needed to map large-scale average flow. The primary technical challenges met in the ALACE design are maximizing energy efficiency to achieve a l...