¹²⁹I/¹²⁷I ratios and iodine concentrations in bovine thyroids stemming from Argentina were determined by accelerator mass spectrometry (AMS) and gas chromatography (GC), respectively. From these measurements, a relationship of the ¹²⁹I/¹²⁷I ratio with iodine content in the gland was obtained. A weak correlation between the two isotopes was found, suggesting that ¹²⁹I re-emission from the ocean is not the only process for the ¹²⁹I deposition in Argentina. Moreover, contributions to the total ¹²⁹I inventory in the Southern hemisphere from both natural and anthropogenic sources were theoretically studied. Surface compartments present similar contribution from natural sources and nuclear explosions fallout.