Climatic forcing of the Southern Ocean deep-sea ecosystem

The deep-time development of the Southern Ocean's deep-sea ecosystem remains poorly understood, despite being a key region in global ecological, climatological, and oceanographic systems, where deep water forms and biodiversity is unexpectedly high.^1,2 Here, we present an ∼500,000-year fossil record of the deep-sea Southern Ocean ecosystem in the subantarctic zone. The results indicate that changes in surface productivity and the resulting food supply to the deep sea, driven by eolian dust input and iron fertilization, along with changes in bottom-water temperature influenced by deep-water circulation, have controlled the deep-sea ecosystem in the Southern Ocean on orbital (10⁴-10⁵ years) timescales following the Mid-Brunhes event (MBE), a major climatic transition ∼430,000 years ago.³ However, before the MBE, the deep-sea Southern Ocean ecosystem was distinct from the present-day, post-MBE one. The present-day form of the deep-sea Southern Ocean ecosystem was established following the MBE, likely because of a stronger incursion of the warm North Atlantic deep water into the Southern Ocean after the MBE. Before that, the deep-sea Southern Ocean ecosystem lacked typical deep-sea faunal components and resembled deep, marginal sea fauna, likely because of the stronger thermal isolation of the Southern Ocean from the Atlantic Ocean. This result suggests that if future human-induced climatic warming weakens global deep-water circulation from the Atlantic through the Southern Ocean to the Pacific,⁴ a deep-sea biodiversity hotspot in the Southern Ocean may diminish or even vanish.