Antarctica has geometric significance for global plate kinematic studies, because it links seafloor spreading systems of the African hemisphere (Indian and Atlantic oceans) with those of the Pacific. The South Pacific plate-motion circuit is closed (observations are internally consistent) for times younger than 33 Ma. Inferences of plate motions back to 43 Ma, around the onset of rapid spreading south of Australia and western New Zealand, are consistent with Antarctic rifting and formation of the Adare Basin. The time period 52-43 Ma represents a profound global and South Pacific tectonic change, and significant details remain unresolved. For 74 Ma, a significant non-closure of the South Pacific plate-motion circuit is identified. Alternate inferences of motion through Antarctica during the interval 83-43 Ma imply significantly different subduction volumes and directions around the Pacific, and imply different relative motions between hotspots.