Reconstructing Export Production in the Subantarctic South Pacific during the Last Ice Age

Despite high concentration of major nutrients in the Southern Ocean, nutrient utilization is inefficient because the scarcity of iron limits phytoplankton growth and primary productivity. Input of eolian dust into the ocean may supply iron, leading to increased export production and nutrient utilization, and potentially affect the Earth’s carbon cycle through its fertilizing effect on marine ecosystem. Recent studies (Martínez-Garcia et al., 2009, 2011, 2014) suggest that iron fertilization in the Subantarctic South Atlantic may have contributed to reducing atmospheric CO2 by ~40ppm over the last glacial cycle. While most of current observations on the Southern Ocean come from the South Atlantic, the Pacific sector covers the largest surface area of the Southern Ocean, indicating its potential to store the largest fraction of carbon. Dust fluxes to the South Atlantic are generally stronger than those to the South Pacific, but the glacial-interglacial pattern of dust deposition is similar. A recent study (Lamy et al., 2014) suggests a ~threefold increase of dust deposition over glacial periods than over interglacial periods in the South Pacific, and show a correlation between dust records and preliminary export production. In this study, we examine a set of cores from the Subantarctic South Pacific at higher temporal resolution to observe variability of export production in response to changing dust flux. We present proxy records for paleoproductivity from excess Ba, biogenic opal and authigenic Uranium. The results will allow us to evaluate the importance of iron fertilization in the Subantarctic Pacific Ocean over glacial/interglacial timescale and its potential effect on the global carbon cycle.