Millennial‐Scale Carbon Flux Variability in the Subantarctic Pacific During Marine Isotope Stage 3 (57–29 ka)

Antarctic ice cores reveal a glacial climate state during Marine Isotope Stage 3 (MIS‐3; 57–29 ka) punctuated by millennial‐scale warming events and pulses of CO 2 . This study further explores how changes in Southern Ocean carbon cycling contributed to these millennial‐scale fluctuations in climate. Evidence from South Atlantic sediment cores suggests that warming events were associated with decreased dust‐borne iron flux, reduced export production, and increased upwelling from the deep Southern Ocean (SO). These processes are considered to have contributed to rising atmospheric CO 2 during periods of rapid warming . Here we investigate whether the same processes occurred in the southwest Pacific sector of the SO at TAN1106‐28. We show that reduced New Zealand glaciation and localized iron limitation in the southwest Pacific led to reduced export production during millennial‐scale warming events. Decreases in foraminifera‐bound δ 15 N during all MIS‐3 warming events may reflect increased nutrient supply by upwelling. Increased calcium carbonate flux during MIS‐3 warming events likely reflects coccolithophore production in response to sea surface temperatures, which, would increase carbonate counter pump strength and reduce CO 2 sequestration. Concomitant decreases in bottom water oxygen, inferred from redox‐sensitive U and Mn sediment concentrations, and increases in the 14 C age of deep waters, suggest that old, nutrient‐rich waters influenced southwest Pacific middepth waters during warming events. This signature may reflect an expansion of Pacific Deep Water into the SO during warming. Taken together, our multi‐proxy data set reveals that the southwest subantarctic Pacific acted as a source of CO 2 during millennial‐scale warming events of MIS‐3.