Implication of eolian delivery and accumulation of highly reactive iron to the Atlantic Ocean

Abstract:

Iron, although abundant in the Earth's crust, is present at low concentrations in sea water and is a limiting nutrient for phytoplankton. Eolian dust (loess) is a major source of this micronutrient, and its deposition has important implications for the global CO₂ budget. In this study, we explore distributions of potentially bioreactive Fe, the soluble fraction required by phytoplankton for photosynthesis and nitrogen assimilation, in deep-sea sediments in the North and South Atlantic Oceans. We used a state-of-the-art Fe speciation technique to characterize Fe inputs from different source regions, specifically North Africa and Patagonia to address the patterns and implications across glacial-interglacial time scales.

 In many open-ocean regions the input of new iron to the surface waters is dominated by the atmospheric deposition of soluble iron in eolian dusts. Multiple records have shown dust accumulation is correlated with glacial-interglacial cycles – glacial periods are substantially dustier. Furthermore, the delivery of eolian dust to the North and South Atlantic Oceans are from two very different source regions and soil types. We analyzed IODP cores from these two regions and our preliminary data shows similar pattern of iron distribution from both the North and South Atlantic Oceans. To date we have found no simple global pattern of bioavailable iron distribution during glacial and interglacial periods. We have analyzed a range of size distributions to isolate the dust-dominated fraction and the data shows no size effects in bioavailable form of iron distribution. We will explore the role of deep-water dust dissolution and sedimentary redox implications and its role on the bioreactive Fe record in marine cores.