Was Subantarctic Dust a Major Driver of Past CO2 Variability?

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Intellectual Merit: The scarcity of iron in seawater can limit the amount of carbon exported from surface to deep waters in areas of the global ocean where the concentration of major nutrients is high, yet phytoplankton growth is low. Of these, the Southern Ocean is the region where variations in iron availability have the largest effect on Earth?s carbon cycle through its fertilizing effect on marine ecosystems. The PIs propose to measure biological productivity and dust flux at five sites spanning the breadth of the Subantarctic Pacific, including one high-resolution site to reconstruct variability of these parameters across abrupt climate change events. These reconstructions will allow the PIs to test whether or not variations in dust flux and changes in biological productivity are correlated in the Subantarctic Pacific as they are in the Subantarctic Atlantic. If they are, results will support current estimates of the iron fertilization effect on lowering CO2. However, if they do not find evidence for iron fertilization in the South Pacific, then the estimated impact of iron fertilization on ice-age CO2 cycles must be reduced and other non- iron fertilization related processes would need to be invoked to account for lower glacial CO2 levels. The results of this study could transform understanding of the role of the Southern Ocean in regulating atmospheric CO2.Broader impacts: This project will foster a strong international collaboration and will train a postdoctoral researcher and two undergraduate students. This research will assess the past response to natural variability of iron input in the largest sector of the Southern Ocean.