Anthropogenic climate change is expected to drive a general depletion of oceanic oxygen in the future. Important insights into the relationship between deoxygenation and warmth can be gleaned from the geological record, but this is currently limited by the sparsity of oxygenation records for oceans under past greenhouse climate conditions. On the other hand, oxygen depletion in the ocean is commonly associated with poor ventilation and storage of respired carbon, potentially linked to lower atmospheric CO2 levels during the ice ages.
Geochemists made numerous attempts to reconstruct seawater redox conditions in the past, but paleoceanographic approaches remain limited. Iodine as a novel proxy has been applied in many geological episodes in recent years. This presentation will focus on one prime example of abrupt warming in greenhouse world (Paleocene-Eocene Thermal Maximum) and one example of well-known cold episodes (Last Glacial Maximum). Planktonic and benthic foraminifera I/Ca data will be shown for both events. The results demonstrate the urgency to refine and cross-examine among different novel oxygenation proxies and to take advantage of the data-model comparison approach.
