Indian Ocean glacial deoxygenation and respired carbon accumulation during mid-late Quaternary ice ages

Reconstructions of ocean oxygenation are critical for understanding the role of respired carbon storage in regulating atmospheric CO₂. Independent sediment redox proxies are essential to assess such reconstructions. Here, we present a long magnetofossil record from the eastern Indian Ocean in which we observe coeval magnetic hardening and enrichment of larger, more elongated, and less oxidized magnetofossils during glacials compared to interglacials over the last ~900 ka. Our multi-proxy records of redox-sensitive magnetofossils, trace element concentrations, and benthic foraminiferal Δδ¹³C consistently suggest a recurrence of lower O₂ in the glacial Indian Ocean over the last 21 marine isotope stages, as has been reported for the Atlantic and Pacific across the last glaciation. Consistent multi-proxy documentation of this repeated oxygen decline strongly supports the hypothesis that increased Indian Ocean glacial carbon storage played a significant role in atmospheric CO₂ cycling and climate change over recent glacial/interglacial timescales.