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Millennial-scale Iron Flux and Ocean Circulation Change Affects Subantarctic Pacific Carbon Cycling During Marine Isotope Stage 3 (57-29 ka)
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  • Harris John Anderson,
  • Zanna Chase,
  • Helen Bostock,
  • Taryn Noble,
  • Rachel Shuttleworth,
  • Bryn Taiapa,
  • Wen-Hui Chen,
  • Haojia Ren,
  • Geraldine E Jacobsen
Harris John Anderson
University of Tasmania

Corresponding Author:[email protected]

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Zanna Chase
University of Tasmania
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Helen Bostock
University of Queensland
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Taryn Noble
University of Tasmania
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Rachel Shuttleworth
University of Southampton
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Bryn Taiapa
Victoria University
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Wen-Hui Chen
National Taiwan University
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Haojia Ren
National Taiwan University
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Geraldine E Jacobsen
Australian Nuclear Science and Technology Organisation
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Abstract

During Marine Isotope Stage 3 (MIS-3; 57–29 ka) Antarctic ice cores reveal a glacial climate state punctuated by millennial-scale warming events and pulses of CO2. Changes in iron-fertilised export production and ocean circulation/upwelling, interpreted from South Atlantic sediment cores, suggest that the Southern Ocean is a conduit for the storage and release of CO2 from the deep ocean. However, it is unclear whether this occurs throughout the Southern Ocean as these processes have not previously been investigated in the southwest Pacific . Here we describe localised iron limitation linked to glaciation changes in New Zealand, which reduced export production during early MIS-3 (60–48 ka) and caused decreases/increases in export production during late MIS-3 (48–29 ka) millennial-scale warming/cooling. Consistent decreases in foraminifera-bound δ15N during all MIS-3 warming events may reflect changes in the supply of nitrate to the subantarctic Pacific, possibly from increased wind-driven upwelling in the Antarctic and northward eddy-driven transport and/or shifting SO fronts. Concomitant decreases in bottom water oxygen and increases in the 14C age of deep waters suggest that old, nutrient-rich waters influenced upper circumpolar deep water in the southwest Pacific during warming events. This signature may reflect an expansion of Pacific Deep Water into the Southern Ocean as Southern Ocean overturning strengthens. Iron-limitation of export production, the expansion of Pacific Deep water, and increased wind-driven upwelling would all work to contribute to increasing atmospheric CO2 through reduced drawdown, and increased outgassing from the Pacific carbon reservoir during the millennial-scale warming events of MIS-3.