Anthropogenic climate change is causing ocean deoxygenation, with tropical Oxygen Minimum Zones (OMZs) expanding at their edges since the mid-to-late 20th century, reducing habitable space for marine life despite significant internal variability. This study finds that the response is regionally asymmetric, with OMZ cores expanding in northern tropical oceans but contracting in the south due to increased ventilation, and highlights the complex and uncertain emergence patterns of climate-driven deoxygenation.