Effect of iron from dust fluxes in the Glacial Southern Ocean

MUGLIA, JUAN; SCHMITTNER, ANDREAS

Simposio; Blowing South: Southern Hemisphere Dust Symposium; 2021

During cold climate periods such as the Last Glacial Maximum (LGM, approximately 20 thousand years before present), ice sheets occupied most of North America and Europe, producing lower sea level than in modern times, and atmospheric carbon was also lower than today. One mechanism proposed to link low atmospheric carbon to glacial periods is an increase in the sinking of organic carbon from the surface Southern Ocean and its accumulation in deep waters. This could have happened through iron, an important nutrient for phytoplankton production that is mostly missing in that region. If iron levels were higher in the LGM, then more phytoplankton would grow, sequestering carbon from the atmosphere, and sinking it to deep waters as dead matter. In this work we use a global ocean model to study differences between the iron cycles of preindustrial times and the LGM. Atmospheric iron fluxes were estimated from reconstructed surface dust fluxes. We find that an increase of atmospheric dust flux to the ocean raised ocean iron in the LGM?s Southern Ocean, increasing productivity and sinking sequestered atmospheric carbon as organic matter. However, we also find that lower sea level in the LGM exposed continental shelves, decreasing the iron flux coming from marine sediments, acting against the other effect.